Daily Coding Problem Solutions
1.0.0
このリポジトリには、Pythonの毎日のコーディング問題ソリューションが含まれています。
サードパーティパッケージをインストールし、次の手順を実行します。
cd Daily-Coding-Problem-Solutionspip install -r requirements.txtを実行します。txt 貢献する前に、拠出ガイドラインをご覧ください。
numpyとmatplotlib 、プレゼンテーションの目的のみに使用されるため、オプションです。数字のリストが与えられた場合、kに2つの合計を返してください。たとえば、[10、15、3、7]と17のKが与えられた場合、10 + 7は17であるためTrueを返します。
ボーナス：これを1回のパスで行うことができますか？
解決
この問題はUberから尋ねられました。
整数の配列が与えられた場合、新しい配列のインデックスIにある各要素が、iのものを除くすべての数値の積であるように新しい配列を返します。
たとえば、入力が[1、2、3、4、5]の場合、予想される出力は[120、60、40、30、24]になります。入力が[3、2、1]の場合、予想される出力は[2、3、6]になります。
フォローアップ：部門を使用できない場合はどうなりますか？
解決
この問題はGoogleから尋ねられました。
バイナリツリーのルートを考えると、シリアル化（ルート）を実装します。これは、ツリーを文字列にシリアル化し、ひもをツリーに戻す脱色（s）にシリアル化します。
解決
この問題はStripeによって尋ねられました。
整数の配列を考えると、線形時間と一定の空間で最初の欠落した正の整数を見つけます。言い換えれば、アレイに存在しない最も低い正の整数を見つけます。アレイには、重複と負の数も含まれている場合があります。
たとえば、入力[3、4、-1、1]は2を与える必要があります。入力[1、2、0]は3を与える必要があります。
入力配列を内部に変更できます。
解決
この問題はジェーン・ストリートから尋ねられました。
短所（a、b）はペアを構築し、車（ペア）とCDR（ペア）はそのペアの最初と最後の要素を返します。たとえば、CAR（CONS（3、4））は3を返し、CDR（CONS（3、4））は4を返します。
この短所の実装を考えると、
def cons ( a , b ):
return lambda f : f ( a , b )車とCDRを実装します。
解決
この問題はGoogleから尋ねられました。
XORリンクリストは、よりメモリ効率の高い二重リンクリストです。次のフィールドと前のフィールドを保持する各ノードの代わりに、次のノードと前のノードのXORである両方の名前のフィールドがあります。 XORリンクリストを実装します。端に要素を追加する追加（要素）と、インデックスでノードを返すget（index）があります。
ポインター（Pythonなど）のない言語を使用する場合、ノードとメモリアドレスを変換するget_pointerおよびdereference_pointer関数にアクセスできると仮定できます。
解決
この問題はFacebookから尋ねられました。
マッピングa = 1、b = 2、... z = 26、およびエンコードされたメッセージを考えると、デコードできる方法の数をカウントします。
たとえば、メッセージ「111」は、「AAA」、「KA」、および「AK」としてデコードできるため、3を与えます。
メッセージがデコード可能であると仮定できます。たとえば、「001」は許可されていません。
解決
この問題はGoogleから尋ねられました。
Unival Tree（「Universal Value」を表す）は、その下のすべてのノードが同じ値を持つツリーです。
バイナリツリーのルートを考えると、ユニバルサブツリーの数をカウントします。
たとえば、次のツリーには5つのユニバルサブツリーがあります。
0
/
1 0
/
1 0
/
1 1
解決
この問題はAirbnbによって尋ねられました。
整数のリストが与えられた場合、非隣接数の最大合計を返す関数を書きます。数値は0または負になる可能性があります。
たとえば、[2、4、6、8]は、4と8を選択するため、12を返す必要があります。[5、1、1、5]は、5と5を選択するため、10を返す必要があります。
解決
この問題はAppleから尋ねられました。
関数fと整数nを取得し、nミリ秒後にfを呼び出すジョブスケジューラを実装します。
解決
この問題はTwitterから尋ねられました。
オートコンプリートシステムを実装します。つまり、クエリ文字列sとすべての可能なクエリ文字列のセットが与えられている場合は、sをプレフィックスとして持つセットのすべての文字列を返します。
たとえば、クエリ文字列deと文字列のセット[犬、鹿、取引]を考えると、return [シカ、ディール]。
ヒント：辞書をより効率的なデータ構造に前処理して、クエリを高速化してみてください。
解決
問題と解決策は、Amazonの著作権侵害のために削除されました
問題と解決策は、Amazonの著作権侵害のために削除されました
この問題はGoogleから尋ねられました。
円の面積はr^2として定義されます。モンテカルロ法を使用して、 piを3桁まで推定します。
ヒント：円の基本方程式はx^2 + y^2 = r^2です。
解決
この問題はFacebookから尋ねられました。
メモリに保存できない要素のストリームが大きすぎると、均一な確率でストリームからランダムな要素を選択します。
解決
この問題はTwitterから尋ねられました。
eコマースのWebサイトを実行し、ログに最後のn注文IDを記録したいと考えています。次のAPIでこれを達成するためにデータ構造を実装してください。
Record（Order_id）：log get_last（i）にorder_idを追加します：logから最後の要素を取得します。私はNよりも小さくなることが保証されています。可能な限り時間と空間で効率的である必要があります。
解決
この問題はGoogleから尋ねられました。
ファイルシステムを次の方法で文字列で表しているとします。
文字列「dir n tsubdir1 n tsubdir2 n t tfile.ext」
dir
subdir1
subdir2
file.ext
ディレクトリ監督には、空のサブディレクトリSubdir1と、file file.extを含むサブディレクトリSubdir2が含まれています。
文字列 "dir n tsubdir1 n t tfile1.ext n t tsubsubdir1 n tsubdir2 n t tsubsubdir2 n t t tfile2.ext"
dir
subdir1
file1.ext
subsubdir1
subdir2
subsubdir2
file2.ext
ディレクトリ監督には、2つのサブディレクトリSubdir1とSubdir2が含まれています。 Subdir1には、ファイルfile1.extと空のセカンドレベルのサブディレクトリSubsubdir1が含まれています。 Subdir2には、ファイルfile2.extを含む第2レベルのサブディレクトリSubsubdir2が含まれています。
ファイルシステム内のファイルへの最長の（文字の数）絶対パスを見つけることに興味があります。たとえば、上記の2番目の例では、最長の絶対パスは「dir/subdir2/subsubdir2/file2.ext」です。その長さは32です（二重引用符は含まれません）。
上記の形式でファイルシステムを表す文字列が与えられた場合、抽象化されたファイルシステムのファイルに最も長い絶対パスの長さを返します。システムにファイルがない場合は、0を返します。
解決
この問題はGoogleから尋ねられました。
整数と数kの配列が与えられ、1 <= k <=配列の長さは、長さkの各サブアレイの最大値を計算します。
たとえば、配列= [10、5、2、7、8、7]およびk = 3を指定すると、[10、7、8、8]を取得する必要があります。
10 = max(10, 5, 2)
7 = max(5, 2, 7)
8 = max(2, 7, 8)
8 = max(7, 8, 7)
これをo（n）時間とo（k）スペースで行います。入力配列を内側に変更でき、結果を保存する必要はありません。それらを計算するときに単に印刷することができます。
解決
この問題はFacebookから尋ねられました。
ビルダーは、k異なる色のn家の列を構築することを検討しています。彼はコストを最小限に抑えながら、2つの隣接する家が同じ色でないことを保証するという目標を持っています。
n行とkth列がkth色のn番目の家を建設するためのコストを表しているk行列によるnを考えると、この目標を達成する最小コストを返します。
解決
この問題はGoogleから尋ねられました。
ある時点で交差する2つの単独でリンクされたリストを考えると、交差するノードを見つけます。リストは非周期的です。
たとえば、a = 3-> 7-> 8-> 8-> 10およびb = 99-> 1-> 8-> 10を指定して、値8でノードを返します。
この例では、同じ値のノードがまったく同じノードオブジェクトであると仮定します。
これをo（m + n）時間（mとnはリストの長さ）と一定の空間で行います。
解決
この問題はSnapchatによって尋ねられました。
教室での講義の時間間隔の配列（開始、終了）が与えられている場合（おそらく重複する可能性が高い）、必要な部屋の最小数を見つけます。
たとえば、[（30、75）、（0、50）、（60、150）]が与えられた場合、2を返す必要があります。
解決
この問題はMicrosoftによって尋ねられました。
単語の辞書とそれらの単語（スペースなし）で構成される文字列を与えられた場合、リストに元の文を返します。可能な再構築が複数ある場合は、それらのいずれかを返してください。再構成が不可能な場合は、nullを返します。
たとえば、「Quick」、「Brown」、「The」、「Fox」、および「TheQuickbrownfox」の単語のセットを考えると、['the'、 'Quick'、 'Brown'、 'Fox'を返す必要があります。 ]。
「ベッド」、「バス」、「ベッドバス」、「」、「、「向こう」、「bedbathandbeyond」の単語のセットを考えると、['bed'、 'bath'、 'and'、 'beyond]のいずれかを返します。または['bedbath'、 'and'、 'beyond']。
解決
この問題はGoogleから尋ねられました。
ボードを表すブール膜で構成されるnマトリックスによってM by n行列が与えられます。それぞれの真のブール値は壁を表します。各誤ったブール値は、歩くことができるタイルを表します。
このマトリックス、開始座標、および終了座標を考慮して、最初からエンド座標に到達するために必要なステップの最小数を返します。可能なパスがない場合は、nullを返します。上に移動し、左、下、右に移動できます。壁を移動することはできません。ボードの端を包むことはできません。
たとえば、次のボードが与えられます。
[[f, f, f, f],
[t, t, f, t],
[f, f, f, f],
[f, f, f, f]]
start =（3、0）（左下）およびend =（0、0）（左上）（左上）、終了に到達するために必要なステップの最小ステップ数は7です（1、2） 2列目にはどこにでも壁があるからです。
解決
この問題はGoogleから尋ねられました。
バイナリツリーにロックを実装します。バイナリツリーノードは、すべての子孫または祖先がロックされていない場合にのみ、ロックまたはロック解除できます。
次の方法でバイナリツリーノードクラスを設計します。
IS_Lockedは、ノードがロックされているかどうかを返し、ノードをロックしようとします。ロックできない場合は、falseを返す必要があります。それ以外の場合は、それをロックしてtrueを返す必要があります。ロックを解除すると、ノードのロックが解除されます。ロック解除できない場合は、falseを返す必要があります。それ以外の場合は、ロックを解除してtrueを返す必要があります。ノードを拡張して、親のポインターまたは他のプロパティを追加することができます。クラスが単一スレッドプログラムで使用されていると仮定することができるため、実際のロックやミューテックスは必要ありません。各メソッドはo（h）で実行する必要があります。ここで、hはツリーの高さです。
解決
この問題はFacebookから尋ねられました。
次の特殊文字との正規表現マッチングを実装してください。
たとえば、正規表現「Ra」が与えられます。そして、文字列「レイ」、あなたの関数はtrueを返すはずです。文字列「レイモンド」の同じ正規表現は、falseを返すはずです。
正規表現".*at"と文字列「チャット」が与えられると、あなたの関数はtrueを返すはずです。文字列「チャット」の同じ正規表現は、falseを返す必要があります。
解決
この問題はGoogleから尋ねられました。
単独でリンクされたリストと整数kを与えられた場合、リストから最後の要素を削除します。 Kは、リストの長さよりも小さくなることが保証されています。
リストは非常に長いので、複数のパスを作ることは法外に高価です。
これを一定のスペースと1つのパスで行います。
解決
この問題はFacebookから尋ねられました。
一連の丸い、巻き毛、正方形の開閉ブラケットと閉じたブラケットが与えられているため、ブラケットのバランスが取れているかどうかを返します（整形式）。
たとえば、文字列「（[]）」が与えられた場合、trueを返す必要があります。
文字列「（[[）]」または「（（（）」が与えられた場合、falseを返す必要があります。
解決
この問題はPalantirによって尋ねられました。
テキストを正当化するアルゴリズムを書きます。一連の単語と整数線の長さkが与えられた場合、完全に正当化された各ラインを表す文字列のリストを返します。
より具体的には、各行にできるだけ多くの単語が必要です。各単語の間に少なくとも1つのスペースがあるはずです。必要に応じて余分なスペースをパッドして、各ラインが正確に長さkになるようにします。スペースは、余分なスペースが左から分布している場合、可能な限り等しく配布する必要があります。
1つの単語しか取り付けられない場合は、スペースで右側にパッドパッドする必要があります。
各単語は、kより長くないことが保証されています。
たとえば、単語のリスト["、" Quick "、" Brown "、" Fox "、" Jumps "、" over "、"、 "lazy"、 "dog"]およびk = 16、以下を返す必要があります。
[「クイックブラウン」、左側の＃1余分なスペース「フォックスがジャンプします」、＃2余分なスペースが均等に分配された「怠zyな犬」]＃4均等に配布される余分なスペース
解決
問題と解決策は、Amazonの著作権侵害のために削除されました
各要素が単位幅の壁であり、整数が高さである2次元標高マップを表す非陰性整数の配列が与えられます。雨が降り、2つの壁の間のすべての斑点が満たされるとします。
O（n）時間とO（1）スペースでマップに閉じ込められた水の数を計算します。
たとえば、入力[2、1、2]を考えると、中央に1単位の水を保持できます。
入力[3、0、1、3、0、5]を考えると、最初のインデックスに3つのユニット、2番目に2つ、4番目のインデックスに3つのユニットを保持できます（5つを保持できません。左）、8ユニットの水を閉じ込めることができます。
解決
この問題はGoogleから尋ねられました。
2つの文字列間の編集距離とは、1つの文字列を他の文字列に変更するために必要な文字挿入、削除、および置換の最小数を指します。たとえば、「子猫」と「座り」の編集距離は3つです。「k」を「k」に置き換え、「e」を「i」に置き換え、「g」を追加します。
2つの文字列を指定して、それらの間の編集距離を計算します。
解決
この問題はジェーン・ストリートから尋ねられました。
2Dアレイとして表される通貨為替レートの表が与えられているとします。可能性のある裁定があるかどうか、つまり、通貨のある程度の金額から始めることができる取引のシーケンスがあるかどうかを判断して、その通貨よりも大きい金額になります。
トランザクションコストはなく、分数の量を取引できます。
解決
この問題はMicrosoftによって尋ねられました。
一連の数値の実行中央値を計算します。つまり、数字のストリームが与えられた場合、それぞれの新しい要素にこれまでのリストの中央値を印刷します。
偶数のリストの中央値は、2つの中間数の平均であることを思い出してください。
たとえば、シーケンス[2、1、5、7、2、0、5]を考えると、アルゴリズムは印刷する必要があります。
2
1.5
2
3.5
2
2
2
解決
この問題はQuoraから尋ねられました。
文字列が与えられた場合、単語のどこにでも可能な限り少数の文字を挿入することで作ることができるパリンドロームを見つけてください。作成できる最小長の1つ以上のパリンドロームがある場合は、辞書編成的に初期のもの（最初のアルファベット順）を返します。
たとえば、文字列の「人種」を考えると、3文字を追加できるため、「ecarace」を返す必要があります（これは、パリンドロームを作るための最小量です）。 3文字を追加することで「人種」から作ることができる他の7つのパリンドロムがありますが、「ecarace」は最初にアルファベット順に登場します。
別の例として、文字列「Google」を考えると、「Elgoogle」を返す必要があります。
解決
この問題はGoogleから尋ねられました。
厳密にキャラクターのr '、「g」、および「b」の配列を考えると、すべてのrsが最初に、GSが2番目になり、BSが最後に来るように、配列の値を分離します。配列の要素のみを交換できます。
これを線形時間とインプレースで行います。
たとえば、配列['g'、 'b'、 'r'、 'r'、 'b'、 'r'、 'g']を考えると、それは['r'、 'r'、 'rになります'、' g '、' g '、' b '、' b ']。
解決
この問題は、Dropboxによって尋ねられました。
バイナリ検索ツリーのルートを考えると、ツリー内の2番目に大きいノードを見つけます。
解決
この問題はGoogleから尋ねられました。
セットの電源セットは、すべてのサブセットのセットです。セットが与えられた関数を書き込み、その電源セットを生成します。
たとえば、セット{1、2、3}を指定すると、{{}、{1}、{2}、{3}、{1、2}、{1、3}、{2、3}を返す必要があります。 、{1、2、3}}。
また、リストまたは配列を使用してセットを表すこともできます。
解決
この問題はMicrosoftによって尋ねられました。
n by nボードがあります。 nが与えられた場合、お互いを脅かすことなくn女王をボードに配置できるボードの可能な手配の数を返す関数を書きます。つまり、2人の女王が同じ行、列、または対角線を共有していません。
解決
この問題は、Dropboxによって尋ねられました。
コンウェイの人生のゲームは、無限の2次元四角細胞のボードで行われます。各セルは死んでいるか生き生きしており、各ティックでは、次のルールが適用されます。
2人未満のライブ隣人が死ぬライブセル。 2つまたは3つの生きている隣人を持つライブセルは残っています。 3人以上のライブネイバーが死ぬライブセル。正確に3つの生きている隣人を持つ死んだセルは、ライブセルになります。細胞隣接は、それが水平、垂直、または斜めに隣接する場合、別の細胞を別の細胞にします。
コンウェイの人生のゲームを実装します。ライブセル座標の開始リストと実行する必要のあるステップ数で初期化できるはずです。初期化したら、各ステップでボード状態を印刷する必要があります。それは無限のボードであるため、関連する座標のみを印刷します。つまり、最も左上のライブセルから最下部のライブセルまで。
アスタリスク*を備えたライブセルとドットのあるデッドセルを表すことができます. 。
解決
この問題はGoogleから尋ねられました。
1つの整数を除き、すべての整数が3回発生する整数の配列が与えられ、1回しか発生しないため、非重複整数を見つけて返します。
たとえば、 [6, 1, 3, 3, 3, 6, 6]が与えられた場合、 1 。 [13, 19, 13, 13]が与えられた場合、 19 。
これを行います
解決
この問題はFacebookから尋ねられました。
それぞれが（原産地、目的地）のペアとして表され、開始空港として表される誰かが撮影したフライトの命令されていないリストを考えると、その人の旅程を計算します。そのような旅程が存在しない場合は、nullを返します。複数の可能な可能な旅程がある場合は、辞書編集的に最小の旅程を返します。すべてのフライトは旅程で使用する必要があります。
たとえば、フライトのリスト[（ 'sfo'、 'hko'）、（ 'yyz'、 'sfo'）、 'yul'、 'yyz'）、 'hko'、 'ord'）、および（ 'yyz'）、および（ 'yyz'）、 「Yul」を開始するには、リスト['Yul'、 'yyz'、 'sfo'、 'hko'、 'ord']を返す必要があります。
フライト[（ 'SFO'、 'com'）、（ 'com'、 'yyz'）]および空港「com」のリストを考えると、nullを返す必要があります。
フライトのリスト[（ 'a'、 'b'）、（ 'a'、 'c'）、（ 'b'、 'c'）、（ 'c'、 'a'）]および開始空港 ' a '、[' a '、' b '、' c '、' a '、' c ']のリストを返す必要があります。 ']も有効な旅程です。ただし、最初のものは辞書編集的に小さくなります。
解決
この問題はGoogleから尋ねられました。
整数sとターゲット番号kのリストが与えられた場合、kに加わるSのサブセットを返す関数を書きます。そのようなサブセットを作成できない場合は、nullを返します。
整数はリストに複数回表示できます。リスト内のすべての数値がプラスであると仮定することができます。
たとえば、 S = [12, 1, 61, 5, 9, 2]およびk = 24が与えられた場合、最大24までの合計で[12、9、2、1]を返します。
解決
問題と解決策は、Amazonの著作権侵害のために削除されました
この問題はGoogleから尋ねられました。
アレイAが、逆転の数をカウントすることにより、どのように「故障」であるかを判断できます。 [i]> a [j]がi <j。つまり、より大きな要素の後に小さな要素が表示されます。
配列を考えると、それが持っている反転の数を数えます。これをO（n^2）時間よりも速くします。
配列内の各要素が異なると仮定することができます。
たとえば、ソートされたリストには反転ゼロがあります。配列[2、4、1、3、5]には、（2、1）、（4、1）、および（4、3）の3つの反転があります。配列[5、4、3、2、1]には10個の反転があります。すべての異なるペアは反転を形成します。
解決
この問題は2つのシグマから尋ねられました。
整数を1から5（包括的）に戻す関数RAND5（）を使用して、均一な確率で、整数を1から7（包括的）に戻す関数RAND7（）を実装します。
解決
問題と解決策は、Amazonの著作権侵害のために削除されました
この問題はFacebookから尋ねられました。
時系列の順序で会社の株価を表す数字の配列を考えると、その株式を一度売買することで得た最大の利益を計算する関数を書きます。売る前に購入する必要があります。
たとえば、[9、11、8、5、7、10]が与えられた場合、5ドルで株式を購入して10ドルで販売できるため、5を返す必要があります。
解決
この問題はGoogleから尋ねられました。
バイナリツリーの予約注文および順序のトラバーサルを指定し、ツリーを再構築する関数を書き込みます。
たとえば、次の予約注文トラバーサルを考慮してください。
[a, b, d, e, c, f, g]
そして、次の注文トラバーサル：
[d, b, e, a, f, c, g]
次のツリーを返す必要があります。
a
/
b c
/ /
d e f g
解決
問題と解決策は、Amazonの著作権侵害のために削除されました
この問題はMicrosoftによって尋ねられました。
算術式がバイナリツリーとして与えられているとします。各葉は整数であり、各内部ノードは「+」、「 - 」、「∗」、または「/」のいずれかです。
そのような木にルートを与えられた場合、それを評価するための関数を書きます。
たとえば、次のツリーが与えられます。
*
/
+ +
/ /
3 2 4 5
（3 + 2） *（4 + 5）のように45を返す必要があります。
解決
この問題はFacebookから尋ねられました。
Kは入力である1とK（包括的）の間に完全に乱数を生成する関数が与えられた場合、スワップのみを使用して配列として表されるカードのデッキをシャッフルする関数を書きます。
O（n）時間で実行する必要があります。
ヒント：52のそれぞれを確認してください！デッキの順列も同様にありそうです。
解決
この問題はGoogleから尋ねられました。
LRU（最近使用されていない）キャッシュを実装します。キャッシュサイズnで初期化し、次の方法を含めることができるはずです。
set（key、value）：キーを値に設定します。キャッシュにnアイテムが既にある場合、新しいアイテムを追加している場合は、最近使用されていないアイテムも削除する必要があります。 get（key）：キーで値を取得します。そのようなキーが存在しない場合は、nullを返します。各操作はO（1）時間で実行する必要があります。
解決
この問題はAppleから尋ねられました。
2つのスタックを使用してキューを実装します。キューは、次の方法を備えたFIFO（ファーストイン、ファーストアウト）データ構造であることを思い出してください：キューに要素を挿入するEnqueueとそれを削除するDequeue。
解決
この問題は、Dropboxによって尋ねられました。
Sudokuはパズルで、桁で部分的に満たされた9 x 9グリッドが与えられています。目的は、すべての行、列、ボックス（3 x 3サブグリッド）が1〜9のすべての数字を含める必要があるという制約でグリッドを埋めることです。
効率的なSudokuソルバーを実装します。
解決
この問題はMicrosoftによって尋ねられました。
次のメソッドを使用してURLショートナーを実装してください。
ヒント：同じURLを2回入力した場合はどうなりますか？
解決
この問題はGoogleから尋ねられました。
隣接するマトリックスと整数Kとして表されている無向グラフが与えられた場合、グラフ内の各頂点を色付けできるかどうかを判断する関数を記述して、ほとんどのk色で2つの隣接する頂点が同じ色を共有しないようにします。
解決
問題と解決策は、Amazonの著作権侵害のために削除されました
問題と解決策は、Amazonの著作権侵害のために削除されました
この問題はGoogleから尋ねられました。
低帯域幅ネットワーク上に2つのコンピューターのファイル同期アルゴリズムを実装します。 2つのコンピューターのファイルがほとんど同じであることがわかったらどうでしょうか？
解決
この問題はFacebookから尋ねられました。
マルチセットの整数を考えると、合計が同じ2つのサブセットに分割できるかどうかを返します。
たとえば、マルチセット{15、5、20、10、35、15、10}を考えると、{15、5、10、15、10}と{20、35に分割できるため、trueを返します。 }、どちらも55になります。
マルチセット{15、5、20、10、35}を考えると、同じ合計に合計する2つのサブセットに分割できないため、Falseを返します。
解決
この問題はGoogleから尋ねられました。
整数指数を実装します。つまり、POW（x、y）関数を実装します。ここで、xとyは整数であり、x^yを返します。
これを繰り返し乗算の素朴な方法よりも速く行います。
たとえば、POW（2、10）は1024を返す必要があります。
解決
この問題はFacebookから尋ねられました。
ゼロのn x mマトリックスがあります。 nとmを考慮して、左上隅から開始して右下隅に到達する方法の数を数えるための関数を書きます。右または下にのみ移動できます。
たとえば、2 x 2マトリックスを考慮して、右下に到達するには2つの方法があるため、2を返す必要があります。
5 x 5マトリックスを考えると、右下に到達するには70の方法があります。
解決
この問題はMicrosoftによって尋ねられました。
文字の2Dマトリックスとターゲットワードが与えられた場合、単語が左から右、または最新の状態になることで、単語がマトリックスにあるかどうかを返す関数を書きます。
たとえば、次のマトリックスが与えられます。
[['F', 'A', 'C', 'I'],
['O', 'B', 'Q', 'P'],
['A', 'N', 'O', 'B'],
['M', 'A', 'S', 'S']]
ターゲットワード「フォーム」は、左端の列であるため、trueを返す必要があります。同様に、ターゲットワード「質量」を考えると、最後の行であるため、trueを返す必要があります。
解決
この問題はGoogleから尋ねられました。
騎士のツアーは、すべての正方形が一度訪れるように、チェス盤の騎士による一連の動きです。
nを考慮して、nチェスボードのnで騎士のツアーの数を返す関数を書きます。
解決
問題と解決策は、Amazonの著作権侵害のために削除されました
この問題はSquareから尋ねられました。
50-50ではない確率で0または1を返す関数Toss_Biased（）にアクセスできると仮定します（0-100または100-0ではありません）。コインのバイアスを知りません。
機能を記述して、公平なコイントスをシミュレートします。
解決
この問題はGoogleから尋ねられました。
LFU（最も頻繁に使用される）キャッシュを実装します。キャッシュサイズnで初期化し、次の方法を含めることができるはずです。
set(key, value) ：キーを値に設定します。キャッシュにnアイテムが既にある場合、新しいアイテムを追加している場合は、頻繁に使用されるアイテムも削除する必要があります。ネクタイがある場合、最近使用されていないキーを削除する必要があります。get(key) ：キーで値を取得します。そのようなキーが存在しない場合は、nullを返します。各操作はO（1）時間で実行する必要があります。
解決
この問題はGoogleから尋ねられました。
私たちの特別なチェスボードでは、2人の司教が同じ対角線を共有している場合、お互いを攻撃します。これには、彼らの間に別の司教がいる司教が含まれます。つまり、司教は破片を攻撃することができます。
あなたは、M by M Chessboardの（列、列）のタプルとして表されるn司教を与えられます。互いに攻撃する司教のペアの数を数えるための関数を書いてください。ペアの順序は関係ありません：（1、2）は（2、1）と同じと見なされます。
たとえば、M = 5と司教のリストが与えられます。
(0, 0)
(1, 2)
(2, 2)
(4, 0)
取締役会は次のようになります：
[b 0 0 0 0]
[0 0 b 0 0]
[0 0 b 0 0]
[0 0 0 0 0]
[b 0 0 0 0]
司教1と3は互いに攻撃し、司教3と4を攻撃するので、2を返す必要があります。
解決
この問題はFacebookから尋ねられました。
整数のリストが与えられた場合、3つの整数を乗算して作成できる最大の製品を返します。
たとえば、リストが[-10、-10、5、2]の場合、-10 _ -10 _ 5であるため、500を返す必要があります。
リストには少なくとも3つの整数があると仮定できます。
解決
数字が正確に10まで合計されている場合、数字は完璧と見なされます。
正の整数nを与えられた場合、n番目の完全な数を返します。
たとえば、1を与えられた場合、19を返す必要があります。2を指定すると、28を返す必要があります。
解決
この問題は2つのシグマから尋ねられました。
整数を1から7（包括的）に戻す関数rand7（）を使用して、均一な確率で整数を実装し、整数を1から5（包括的）に戻す関数rand5（）を実装します。
（繰り返し質問 - 問題45）
解決
この問題はGoogleから尋ねられました。
指示されたグラフでは、各ノードに大文字が割り当てられています。パスの値を、そのパスに沿って最も頻繁に発生する文字の数として定義します。たとえば、グラフ内のパスが「アバカ」を通過する場合、パスに3つの「a」が発生するため、パスの値は3です。
nノードとm方向のエッジを備えたグラフが与えられた場合、グラフの最大の値パスを返します。最大の値が無限の場合は、nullを返します。
グラフは、文字列とエッジリストで表されます。 i番目の文字は、i番目のノードの大文字を表します。エッジリスト（i、j）の各タプルは、i番目のノードからj番目のノードまでの指向性エッジがあることを意味します。自己エッジは、マルチエッジだけでなく可能です。
たとえば、次の入力グラフ：
ABACA
[(0, 1),
(0, 2),
(2, 3),
(3, 4)]
頂点[0, 2, 3, 4], (A, A, C, A)のパスを使用して最大値3を使用します。
次の入力グラフ：
A
[(0, 0)]
無限のループがあるため、nullを返す必要があります。
解決
この問題はGoogleから尋ねられました。
単独でリンクされたリストのヘッドを考えると、その場所を逆にします。
解決
この問題はAppleから尋ねられました。
Nがnの乗算テーブルを持っているとします。つまり、i行列とj-th列の値が（i + 1）_（j + 1）（0インデックスの場合）である2D配列があります。またはi _ j（1インデックスした場合）。
integers nとxを指定した場合、x回数xを返す関数を書き込み、n n by nの乗算表の値として表示します。
たとえば、n = 6およびx = 12を指定すると、乗算テーブルは次のようになるため、4を返す必要があります。
| 1 | 2 | 3 | 4 | 5 | 6 |
| 2 | 4 | 6 | 8 | 10 | 12 |
| 3 | 6 | 9 | 12 | 15 | 18 |
| 4 | 8 | 12 | 16 | 20 | 24 |
| 5 | 10 | 15 | 20 | 25 | 30 |
| 6 | 12 | 18 | 24 | 30 | 36 |
テーブルには4つの12があります。
解決
この問題はMicrosoftによって尋ねられました。
数字の配列を考えると、アレイ内の最長のサブシーケンスの長さを見つけます。サブシーケンスは必ずしも隣接する必要はありません。
たとえば、配列[0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15]考えると、最長の増加サブシーケンスは長さ6です。 0, 2, 6, 9, 11, 15 。
解決
この問題はGoogleから尋ねられました。
小文字のM 2Dマトリックスによってnが与えられます。各行が上から下部まで辞書編成的に注文されることを確認するために、削除できる列の最小数を決定します。つまり、各列の文字は、各列を下ると辞書的に後で説明します。各行自体が辞書的に注文されるかどうかは関係ありません。
たとえば、次の表を示します。
cba
daf
ghi
これは、中央のAのために注文されていません。 2番目の列を削除して注文することができます。
ca
df
gi
したがって、1列を削除する必要があるため、関数は1を返す必要があります。
別の例として、次の表を示します。
abcdef
行はすでに注文されているため、関数は0を返す必要があります（1つの行があります）。
別の例として、次の表を示します。
zyx
wvu
tsr
すべての列を削除して注文する必要があるため、関数は3を返す必要があります。
解決
この問題はSnapchatによって尋ねられました。
重複する間隔の可能性のあるリストが与えられた場合、すべての重複する間隔がマージされている間隔の新しいリストを返します。
入力リストは、必ずしも何らかの形で注文されるわけではありません。
たとえば、 [(1, 3), (5, 8), (4, 10), (20, 25)]が与えられた場合[(1, 3), (4, 10), (20, 25)]を返す必要があります。 [(1, 3), (4, 10), (20, 25)] 。
解決
この問題は最近Googleから尋ねられました。
kソートされた単独でリンクされたリストを考慮して、関数を書き込み、すべてのリストを1つのソートされた単独リンクリストにマージします。
解決
この問題はFacebookから尋ねられました。
整数の配列が与えられた場合、関数を記述して、最大1要素を変更することにより、配列が非廃止になるかどうかを判断します。
たとえば、配列[10, 5, 7]を考慮して、10を1に変更してアレイを非脱落にすることができるため、trueを返す必要があります。
Given the array [10, 5, 1] , you should return false, since we can't modify any one element to get a non-decreasing array.
解決
This problem was asked by Google.
Given the root of a binary tree, return a deepest node. For example, in the following tree, return d.
a
/
b c
/
d
解決
This problem was asked by Yelp.
Given a mapping of digits to letters (as in a phone number), and a digit string, return all possible letters the number could represent. You can assume each valid number in the mapping is a single digit.
For example if {'2': ['a', 'b', 'c'], '3': ['d', 'e', 'f'], } then "23" should return ['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf'] .
解決
This problem was asked Microsoft.
Using a read7() method that returns 7 characters from a file, implement readN(n) which reads n characters.
For example, given a file with the content "Hello world", three read7() returns "Hello w", "orld" and then "".
解決
This problem was asked by Google.
Invert a binary tree.
For example, given the following tree:
a
/
b c
/ /
d e f
should become:
a
/
c b
/
f e d
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Facebook.
Given three 32-bit integers x, y, and b, return x if b is 1 and y if b is 0, using only mathematical or bit operations. You can assume b can only be 1 or 0.
解決
This problem was asked by Google.
Given a string of parentheses, write a function to compute the minimum number of parentheses to be removed to make the string valid (ie each open parenthesis is eventually closed).
For example, given the string "()())()", you should return 1. Given the string ")(", you should return 2, since we must remove all of them.
解決
This problem was asked by Uber.
A rule looks like this:
A NE B
This means this means point A is located northeast of point B.
A SW C
means that point A is southwest of C.
Given a list of rules, check if the sum of the rules validate.例えば：
A N B
B NE C
C N A
does not validate, since A cannot be both north and south of C.
A NW B
A N B
is considered valid.
解決
This question was asked by ContextLogic.
Implement division of two positive integers without using the division, multiplication, or modulus operators. Return the quotient as an integer, ignoring the remainder.
解決
This problem was asked by LinkedIn.
Determine whether a tree is a valid binary search tree.
A binary search tree is a tree with two children, left and right, and satisfies the constraint that the key in the left child must be less than or equal to the root and the key in the right child must be greater than or equal to the根。
解決
This question was asked by Google.
Given an integer n and a list of integers l, write a function that randomly generates a number from 0 to n-1 that isn't in l (uniform).
解決
This problem was asked by Dropbox.
What does the below code snippet print out? How can we fix the anonymous functions to behave as we'd expect?
functions = []
for i in range ( 10 ):
functions . append ( lambda : i )
for f in functions :
print ( f ())解決
This problem was asked by Airbnb.
We're given a hashmap with a key courseId and value a list of courseIds, which represents that the prerequsite of courseId is courseIds. Return a sorted ordering of courses such that we can finish all courses.
Return null if there is no such ordering.
For example, given {'CSC300': ['CSC100', 'CSC200'], 'CSC200': ['CSC100'], 'CSC100': []} , should return ['CSC100', 'CSC200', 'CSCS300'] .
解決
This problem was asked by Apple.
Given a tree, find the largest tree/subtree that is a BST.
Given a tree, return the size of the largest tree/subtree that is a BST.
解決
This problem was asked by Google.
Given a binary tree of integers, find the maximum path sum between two nodes. The path must go through at least one node, and does not need to go through the root.
解決
This problem was asked by Palantir.
Given a number represented by a list of digits, find the next greater permutation of a number, in terms of lexicographic ordering. If there is not greater permutation possible, return the permutation with the lowest value/ordering.
For example, the list [1,2,3] should return [1,3,2] . The list [1,3,2] should return [2,1,3] . The list [3,2,1] should return [1,2,3] .
Can you perform the operation without allocating extra memory (disregarding the input memory)?
解決
This problem was asked by Microsoft.
Given a number in the form of a list of digits, return all possible permutations.
For example, given [1,2,3] , return [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]] .
解決
This problem was asked by Stripe.
Write a map implementation with a get function that lets you retrieve the value of a key at a particular time.
It should contain the following methods:
set(key, value, time): # sets key to value for t = time.
get(key, time): # gets the key at t = time.
The map should work like this. If we set a key at a particular time, it will maintain that value forever or until it gets set at a later time. In other words, when we get a key at a time, it should return the value that was set for that key set at the most recent time.
Consider the following examples:
d.set(1, 1, 0) # set key 1 to value 1 at time 0
d.set(1, 2, 2) # set key 1 to value 2 at time 2
d.get(1, 1) # get key 1 at time 1 should be 1
d.get(1, 3) # get key 1 at time 3 should be 2
d.set(1, 1, 5) # set key 1 to value 1 at time 5
d.get(1, 0) # get key 1 at time 0 should be null
d.get(1, 10) # get key 1 at time 10 should be 1
d.set(1, 1, 0) # set key 1 to value 1 at time 0
d.set(1, 2, 0) # set key 1 to value 2 at time 0
d.get(1, 0) # get key 1 at time 0 should be 2
解決
This problem was asked by Coursera.
Given a 2D board of characters and a word, find if the word exists in the grid.
The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.
For example, given the following board:
[
['A','B','C','E'],
['S','F','C','S'],
['A','D','E','E']
]
exists(board, "ABCCED") returns true, exists(board, "SEE") returns true, exists(board, "ABCB") returns false.
解決
This problem was asked by Microsoft.
Given an unsorted array of integers, find the length of the longest consecutive elements sequence.
For example, given [100, 4, 200, 1, 3, 2], the longest consecutive element sequence is [1, 2, 3, 4]. Return its length: 4.
Your algorithm should run in O(n) complexity.
解決
This problem was asked by Google.
You are in an infinite 2D grid where you can move in any of the 8 directions:
(x,y) to
(x+1, y),
(x - 1, y),
(x, y+1),
(x, y-1),
(x-1, y-1),
(x+1,y+1),
(x-1,y+1),
(x+1,y-1)
You are given a sequence of points and the order in which you need to cover the points. Give the minimum number of steps in which you can achieve it. You start from the first point.
Example: Input: [(0, 0), (1, 1), (1, 2)] Output: 2 It takes 1 step to move from (0, 0) to (1, 1). It takes one more step to move from (1, 1) to (1, 2).
解決
This problem was asked by Alibaba.
Given an even number (greater than 2), return two prime numbers whose sum will be equal to the given number.
A solution will always exist. See Goldbach's conjecture.
例：
Input: 4 Output: 2 + 2 = 4 If there are more than one solution possible, return the lexicographically smaller solution.
If [a, b] is one solution with a <= b , and [c, d] is another solution with c <= d , then
[ a , b ] < [ c , d ]
if a < c or a == c and b < d .解決
This problem was asked by Lyft.
Given a list of integers and a number K, return which contiguous elements of the list sum to K.
For example, if the list is [1, 2, 3, 4, 5] and K is 9, then it should return [2, 3, 4].
解決
This problem was asked by Square.
Given a string and a set of characters, return the shortest substring containing all the characters in the set.
For example, given the string "figehaeci" and the set of characters {a, e, i}, you should return "aeci".
If there is no substring containing all the characters in the set, return null.
解決
This problem was asked by Google.
Determine whether a doubly linked list is a palindrome. What if it's singly linked?
For example, 1 -> 4 -> 3 -> 4 -> 1 returns true while 1 -> 4 returns false.
解決
This problem was asked by Facebook.
Given a function f, and N return a debounced f of N milliseconds.
That is, as long as the debounced f continues to be invoked, f itself will not be called for N milliseconds.
解決
This problem was asked by Pinterest.
Given an integer list where each number represents the number of hops you can make, determine whether you can reach to the last index starting at index 0.
For example, [2, 0, 1, 0] returns true while [1, 1, 0, 1] returns false .
解決
This problem was asked by Microsoft.
Print the nodes in a binary tree level-wise. For example, the following should print 1, 2, 3, 4, 5 .
1
/
2 3
/
4 5
解決
This problem was asked by Google.
Given two strings A and B, return whether or not A can be shifted some number of times to get B.
For example, if A is abcde and B is cdeab , return true. If A is abc and B is acb , return false.
解決
This problem was asked by Cisco.
Given an unsigned 8-bit integer, swap its even and odd bits. The 1st and 2nd bit should be swapped, the 3rd and 4th bit should be swapped, and so on.
For example, 10101010 should be 01010101 . 11100010 should be 11010001 .
Bonus: Can you do this in one line?
解決
This problem was asked by Facebook.
Given a binary tree, return all paths from the root to leaves.
For example, given the tree
1
/
2 3
/
4 5
it should return [[1, 2], [1, 3, 4], [1, 3, 5]] .
解決
This problem was asked by Google.
Given a word W and a string S, find all starting indices in S which are anagrams of W.
For example, given that W is "ab", and S is "abxaba", return 0, 3, and 4.
解決
This problem was asked by Twitter.
Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree. Assume that each node in the tree also has a pointer to its parent.
According to the definition of LCA on Wikipedia: "The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself). 「
解決
This problem was asked by Google.
Given a string of words delimited by spaces, reverse the words in string. For example, given "hello world here", return "here world hello"
Follow-up: given a mutable string representation, can you perform this operation in-place?
解決
This problem was asked by Facebook.
Given a string and a set of delimiters, reverse the words in the string while maintaining the relative order of the delimiters. For example, given "hello/world:here", return "here/world:hello"
Follow-up: Does your solution work for the following cases: "hello/world:here/", "hello//world:here"
解決
This problem was asked by Google.
Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.
解決
This problem was asked by Jane Street.
Generate a finite, but an arbitrarily large binary tree quickly in O(1) .
That is, generate() should return a tree whose size is unbounded but finite.
解決
This problem was asked by Facebook.
Given a binary tree, return the level of the tree with minimum sum.
解決
This problem was asked by Google.
Given a sorted list of integers, square the elements and give the output in sorted order.
For example, given [-9, -2, 0, 2, 3] , return [0, 4, 4, 9, 81] .
解決
This problem was asked by Google.
Given a set of closed intervals, find the smallest set of numbers that covers all the intervals. If there are multiple smallest sets, return any of them.
For example, given the intervals [0, 3], [2, 6], [3, 4], [6, 9] , one set of numbers that covers all these intervals is {3, 6} .
解決
This problem was asked by Microsoft.
Implement the singleton pattern with a twist. First, instead of storing one instance, store two instances. And in every even call of getInstance(), return the first instance and in every odd call of getInstance(), return the second instance.
解決
This problem was asked by Google.
Given a string which we can delete at most k, return whether you can make a palindrome.
For example, given 'waterrfetawx' and ak of 2, you could delete f and x to get 'waterretaw'.
解決
This question was asked by Zillow.
You are given a 2-d matrix where each cell represents number of coins in that cell. Assuming we start at matrix[0][0] , and can only move right or down, find the maximum number of coins you can collect by the bottom right corner.
For example, in this matrix
0 3 1 1
2 0 0 4
1 5 3 1
The most we can collect is 0 + 2 + 1 + 5 + 3 + 1 = 12 coins.
解決
This problem was asked by LinkedIn.
Given a string, return whether it represents a number. Here are the different kinds of numbers:
And here are examples of non-numbers:
解決
This problem was asked by Microsoft.
You have 100 fair coins and you flip them all at the same time. Any that come up tails you set aside. The ones that come up heads you flip again. How many rounds do you expect to play before only one coin remains?
Write a function that, given
解決
This problem was asked by Google.
Given the root of a binary search tree, and a target K, return two nodes in the tree whose sum equals K.
For example, given the following tree and K of 20
10
/
5 15
/
11 15
Return the nodes 5 and 15.
解決
This problem was asked by Facebook.
Write a function that rotates a list by k elements. For example, [1, 2, 3, 4, 5, 6] rotated by two becomes [3, 4, 5, 6, 1, 2] . Try solving this without creating a copy of the list. How many swap or move operations do you need?
解決
This problem was asked by Microsoft.
Let's represent an integer in a linked list format by having each node represent a digit in the number. The nodes make up the number in reversed order.
For example, the following linked list:
1 -> 2 -> 3 -> 4 -> 5 is the number 54321 .
Given two linked lists in this format, return their sum in the same linked list format.
For example, given
9 -> 9 5 -> 2 return 124 (99 + 25) as:
4 -> 2 -> 1
解決
The Tower of Hanoi is a puzzle game with three rods and n disks, each a different size.
All the disks start off on the first rod in a stack. They are ordered by size, with the largest disk on the bottom and the smallest one at the top.
The goal of this puzzle is to move all the disks from the first rod to the last rod while following these rules:
Write a function that prints out all the steps necessary to complete the Tower of Hanoi. You should assume that the rods are numbered, with the first rod being 1, the second (auxiliary) rod being 2, and the last (goal) rod being 3.
For example, with n = 3, we can do this in 7 moves:
解決
Given a real number n, find the square root of n. For example, given n = 9, return 3.
解決
This problem was asked by Facebook.
Given an array of numbers representing the stock prices of a company in chronological order and an integer k, return the maximum profit you can make from k buys and sells. You must buy the stock before you can sell it, and you must sell the stock before you can buy it again.
For example, given k = 2 and the array [5, 2, 4, 0, 1] , you should return 3 .
解決
This question was asked by Snapchat.
Given the head to a singly linked list, where each node also has a 'random' pointer that points to anywhere in the linked list, deep clone the list.
解決
This question was asked by Riot Games.
Design and implement a HitCounter class that keeps track of requests (or hits). It should support the following operations:
record(timestamp) : records a hit that happened at timestamptotal() : returns the total number of hits recordedrange(lower, upper) : returns the number of hits that occurred between timestamps lower and upper (inclusive)Follow-up: What if our system has limited memory?
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Facebook.
You have a large array with most of the elements as zero.
Use a more space-efficient data structure, SparseArray, that implements the same interface:
init(arr, size) : initialize with the original large array and size.set(i, val) : updates index at i with val.get(i) : gets the value at index i.解決
This question was asked by Apple.
Given a binary tree, find a minimum path sum from root to a leaf.
For example, the minimum path in this tree is [10, 5, 1, -1] , which has sum 15.
10
/
5 5
2 1
/
-1
解決
This question was asked by Google.
Given an N by M matrix consisting only of 1's and 0's, find the largest rectangle containing only 1's and return its area.
For example, given the following matrix:
[[1, 0, 0, 0],
[1, 0, 1, 1],
[1, 0, 1, 1],
[0, 1, 0, 0]]
Return 4.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Google.
Find the minimum number of coins required to make n cents.
You can use standard American denominations, that is, 1¢, 5¢, 10¢, and 25¢.
For example, given n = 16, return 3 since we can make it with a 10¢, a 5¢, and a 1¢.
解決
This problem was asked by Google.
Given an iterator with methods next() and hasNext(), create a wrapper iterator, PeekableInterface, which also implements peek(). peek shows the next element that would be returned on next().
Here is the interface:
class PeekableInterface(object):
def __init__(self, iterator):
pass
def peek(self):
pass
def next(self):
pass
def hasNext(self):
pass
解決
This problem was asked by Facebook.
Given an array of integers in which two elements appear exactly once and all other elements appear exactly twice, find the two elements that appear only once.
For example, given the array [2, 4, 6, 8, 10, 2, 6, 10] , return 4 and 8. The order does not matter.
Follow-up: Can you do this in linear time and constant space?
解決
This problem was asked by Microsoft.
Implement 3 stacks using a single list:
class Stack:
def __init__(self):
self.list = []
def pop(self, stack_number):
pass
def push(self, item, stack_number):
pass
解決
This problem was asked by Google.
You're given a string consisting solely of ( , ) , and * . * can represent either a ( , ) , or an empty string. Determine whether the parentheses are balanced.
For example, (()* and (*) are balanced. )*( is not balanced.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Google.
Given an array of numbers and an index i , return the index of the nearest larger number of the number at index i , where distance is measured in array indices.
For example, given [4, 1, 3, 5, 6] and index 0 , you should return 3 .
If two distances to larger numbers are equal, then return any one of them. If the array at i doesn't have a nearest larger integer, then return null .
Follow-up: If you can preprocess the array, can you do this in constant time?
解決
This problem was asked by Google.
Given the head of a singly linked list, swap every two nodes and return its head.
For example, given 1 -> 2 -> 3 -> 4 , return 2 -> 1 -> 4 -> 3 .
解決
This question was asked by BufferBox.
Given a binary tree where all nodes are either 0 or 1, prune the tree so that subtrees containing all 0s are removed.
For example, given the following tree:
0
/
1 0
/
1 0
/
0 0
should be pruned to:
0
/
1 0
/
1
We do not remove the tree at the root or its left child because it still has a 1 as a descendant.
解決
Given a list, sort it using this method: reverse(lst, i, j) , which sorts lst from i to j .
解決
This problem was asked by Apple.
Gray code is a binary code where each successive value differ in only one bit, as well as when wrapping around. Gray code is common in hardware so that we don't see temporary spurious values during transitions.
Given a number of bits n , generate a possible gray code for it.
For example, for n = 2 , one gray code would be [00, 01, 11, 10] .
解決
This problem was asked by Goldman Sachs.
Given a list of numbers L , implement a method sum(i, j) which returns the sum from the sublist L[i:j] (including i, excluding j).
For example, given L = [1, 2, 3, 4, 5] , sum(1, 3) should return sum([2, 3]) , which is 5 .
You can assume that you can do some pre-processing. sum() should be optimized over the pre-processing step.
解決
This problem was asked by LinkedIn.
Given a list of points, a central point, and an integer k, find the nearest k points from the central point.
For example, given the list of points [(0, 0), (5, 4), (3, 1)] , the central point (1, 2) , and k = 2 , return [(0, 0), (3, 1)] .
解決
Given a 2-D matrix representing an image, a location of a pixel in the screen and a color C, replace the color of the given pixel and all adjacent same colored pixels with C.
For example, given the following matrix, and location pixel of (2, 2) , and 'G' for green:
B B W
W W W
W W W
B B B
Becomes
B B G
G G G
G G G
B B B
解決
This problem was asked by Triplebyte.
You are given n numbers as well as n probabilities that sum up to 1 . Write a function to generate one of the numbers with its corresponding probability.
For example, given the numbers [1, 2, 3, 4] and probabilities [0.1, 0.5, 0.2, 0.2] , your function should return 1 10% of the time, 2 50% of the time, and 3 and 4 20% of the time.
You can generate random numbers between 0 and 1 uniformly.
解決
Find an efficient algorithm to find the smallest distance (measured in number of words) between any two given words in a string.
For example, given words "hello", and "world" and a text content of "dog cat hello cat dog dog hello cat world", return 1 because there's only one word "cat" in between the two words.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
Given a list of elements, find the majority element, which appears more than half the times (> floor(len(lst) / 2.0)) .
You can assume that such an element exists.
For example, given [1, 2, 1, 1, 3, 4, 0] , return 1 .
解決
This problem was asked by Facebook.
Given a positive integer n , find the smallest number of squared integers which sum to n .
For example, given n = 13 , return 2 since 13 = 3^2 + 2^2 = 9 + 4 .
Given n = 27 , return 3 since 27 = 3^2 + 3^2 + 3^2 = 9 + 9 + 9 .
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Slack.
You are given an N * M matrix of 0 s and 1 s. Starting from the top left corner, how many ways are there to reach the bottom right corner?
You can only move right and down. 0 represents an empty space while 1 represents a wall you cannot walk through.
For example, given the following matrix:
[[0, 0, 1],
[0, 0, 1],
[1, 0, 0]]
Return 2 , as there are only two ways to get to the bottom right:
Right, down, down, rightDown, right, down, right The top left corner and bottom right corner will always be 0 .
解決
This problem was asked by Google.
Given a string, return the first recurring character in it, or null if there is no recurring chracter.
For example, given the string "acbbac" , return "b" . Given the string "abcdef" , return null .
解決
This problem was asked by Uber.
Given a tree where each edge has a weight, compute the length of the longest path in the tree.
For example, given the following tree:
a
/|
b c d
/
e f
/
g h
and the weights: ab: 3 , ac: 5 , ad: 8 , de: 2 , df: 4 , eg: 1 , eh: 1 , the longest path would be c -> a -> d -> f , with a length of 17 .
The path does not have to pass through the root, and each node can have any amount of children.
解決
This problem was asked by Facebook.
Given a 32-bit integer, return the number with its bits reversed.
For example, given the binary number 1111 0000 1111 0000 1111 0000 1111 0000 , return 0000 1111 0000 1111 0000 1111 0000 1111 .
解決
This problem was asked by Square.
Given a list of words, return the shortest unique prefix of each word. For example, given the list:
Return the list:
解決
This problem was asked by Jane Street.
Given an arithmetic expression in Reverse Polish Notation, write a program to evaluate it.
The expression is given as a list of numbers and operands. For example: [5, 3, '+'] should return 5 + 3 = 8 .
For example, [15, 7, 1, 1, '+', '-', '/', 3, '*', 2, 1, 1, '+', '+', '-'] should return 5 , since it is equivalent to ((15 / (7 - (1 + 1))) * 3) - (2 + (1 + 1)) = 5 .
You can assume the given expression is always valid.
解決
This problem was asked by Google.
You are given an array of length n + 1 whose elements belong to the set {1, 2, ..., n} . By the pigeonhole principle, there must be a duplicate. Find it in linear time and space.
解決
This problem was asked by Google.
Given an array of integers, return a new array where each element in the new array is the number of smaller elements to the right of that element in the original input array.
For example, given the array [3, 4, 9, 6, 1] , return [1, 1, 2, 1, 0] , since:
34961解決
This problem was asked by Uber.
Implement a 2D iterator class. It will be initialized with an array of arrays, and should implement the following methods:
next() : returns the next element in the array of arrays. If there are no more elements, raise an exception.has_next() : returns whether or not the iterator still has elements left. For example, given the input [[1, 2], [3], [], [4, 5, 6]] , calling next() repeatedly should output 1, 2, 3, 4, 5, 6 .
Do not use flatten or otherwise clone the arrays. Some of the arrays can be empty.
解決
This problem was asked by Airbnb.
Given a list of words, find all pairs of unique indices such that the concatenation of the two words is a palindrome.
For example, given the list ["code", "edoc", "da", "d"] , return [(0, 1), (1, 0), (2, 3)] .
解決
This problem was asked by Facebook.
Given an N by N matrix, rotate it by 90 degrees clockwise.
For example, given the following matrix:
[[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
you should return:
[[7, 4, 1],
[8, 5, 2],
[9, 6, 3]]
Follow-up: What if you couldn't use any extra space?
解決
This problem was asked by Google.
Given a linked list, sort it in O(n log n) time and constant space.
For example, the linked list 4 -> 1 -> -3 -> 99 should become -3 -> 1 -> 4 -> 99 .
解決
This problem was asked by Facebook.
Given a start word, an end word, and a dictionary of valid words, find the shortest transformation sequence from start to end such that only one letter is changed at each step of the sequence, and each transformed word exists in the dictionary. If there is no possible transformation, return null. Each word in the dictionary have the same length as start and end and is lowercase.
For example, given start = "dog" , end = "cat" , and dictionary = {"dot", "dop", "dat", "cat"} , return ["dog", "dot", "dat", "cat"] 。
Given start = "dog" , end = "cat" , and dictionary = {"dot", "tod", "dat", "dar"} , return null as there is no possible transformation from dog to cat.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Dropbox.
Given a string s and a list of words words , where each word is the same length, find all starting indices of substrings in s that is a concatenation of every word in words exactly once.
For example, given s = "dogcatcatcodecatdog" and words = ["cat", "dog"] , return [0, 13] , since "dogcat" starts at index 0 and "catdog" starts at index 13 .
Given s = "barfoobazbitbyte" and words = ["dog", "cat"] , return [] since there are no substrings composed of "dog" and "cat" in s .
The order of the indices does not matter.
解決
This problem was asked by Stripe.
Write a function to flatten a nested dictionary. Namespace the keys with a period.
For example, given the following dictionary:
{
"key": 3,
"foo": {
"a": 5,
"bar": {
"baz": 8
}
}
}
it should become:
{
"key": 3,
"foo.a": 5,
"foo.bar.baz": 8
}
You can assume keys do not contain dots in them, ie no clobbering will occur.
解決
This problem was asked by Microsoft.
Describe and give an example of each of the following types of polymorphism:
解決
This problem was asked by Google.
You are given a starting state start, a list of transition probabilities for a Markov chain, and a number of steps num_steps. Run the Markov chain starting from start for num_steps and compute the number of times we visited each state.
For example, given the starting state a , number of steps 5000 , and the following transition probabilities:
[
('a', 'a', 0.9),
('a', 'b', 0.075),
('a', 'c', 0.025),
('b', 'a', 0.15),
('b', 'b', 0.8),
('b', 'c', 0.05),
('c', 'a', 0.25),
('c', 'b', 0.25),
('c', 'c', 0.5)
]
One instance of running this Markov chain might produce {'a': 3012, 'b': 1656, 'c': 332 } .
解決
This problem was asked by Bloomberg.
Determine whether there exists a one-to-one character mapping from one string s1 to another s2 .
For example, given s1 = abc and s2 = bcd , return true since we can map a to b , b to c , and c to d .
Given s1 = foo and s2 = bar , return false since the o cannot map to two characters.
解決
This problem was asked by Airbnb.
Given a linked list and a positive integer k , rotate the list to the right by k places.
For example, given the linked list 7 -> 7 -> 3 -> 5 and k = 2 , it should become 3 -> 5 -> 7 -> 7 .
Given the linked list 1 -> 2 -> 3 -> 4 -> 5 and k = 3 , it should become 3 -> 4 -> 5 -> 1 -> 2 .
解決
This problem was asked by Two Sigma.
Alice wants to join her school's Probability Student Club. Membership dues are computed via one of two simple probabilistic games.
The first game: roll a die repeatedly. Stop rolling once you get a five followed by a six. Your number of rolls is the amount you pay, in dollars.
The second game: same, except that the stopping condition is a five followed by a five.
Which of the two games should Alice elect to play? Does it even matter? Write a program to simulate the two games and calculate their expected value.
解決
This problem was asked by Google.
Given the sequence of keys visited by a postorder traversal of a binary search tree, reconstruct the tree.
For example, given the sequence 2, 4, 3, 8, 7, 5 , you should construct the following tree:
5
/
3 7
/
2 4 8
解決
This problem was asked by Google.
Given a stack of N elements, interleave the first half of the stack with the second half reversed using only one other queue. This should be done in-place.
Recall that you can only push or pop from a stack, and enqueue or dequeue from a queue.
For example, if the stack is [1, 2, 3, 4, 5] , it should become [1, 5, 2, 4, 3] . If the stack is [1, 2, 3, 4] , it should become [1, 4, 2, 3] .
Hint: Try working backwards from the end state.
解決
This problem was asked by Google.
Given a string, split it into as few strings as possible such that each string is a palindrome.
For example, given the input string "racecarannakayak" , return ["racecar", "anna", "kayak"] .
Given the input string "abc" , return ["a", "b", "c"] .
解決
This problem was asked by Facebook.
A graph is minimally-connected if it is connected and there is no edge that can be removed while still leaving the graph connected. For example, any binary tree is minimally-connected.
Given an undirected graph, check if the graph is minimally-connected. You can choose to represent the graph as either an adjacency matrix or adjacency list.
解決
This problem was asked by Twitch.
Describe what happens when you type a URL into your browser and press Enter.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Google.
Given two rectangles on a 2D graph, return the area of their intersection. If the rectangles don't intersect, return 0 .
For example, given the following rectangles:
{
"top_left": (1, 4),
"dimensions": (3, 3) # width, height
}
そして
{
"top_left": (0, 5),
"dimensions" (4, 3) # width, height
}
return 6 .
解決
This problem was asked by Microsoft.
Given an array of positive integers, divide the array into two subsets such that the difference between the sum of the subsets is as small as possible.
For example, given [5, 10, 15, 20, 25] , return the sets {10, 25} and {5, 15, 20} , which has a difference of 5 , which is the smallest possible difference.
解決
This problem was asked by Google.
You are given given a list of rectangles represented by min and max x- and y-coordinates. Compute whether or not a pair of rectangles overlap each other. If one rectangle completely covers another, it is considered overlapping.
For example, given the following rectangles:
{
"top_left": (1, 4),
"dimensions": (3, 3) # width, height
},
{
"top_left": (-1, 3),
"dimensions": (2, 1)
},
{
"top_left": (0, 5),
"dimensions": (4, 3)
}
return true as the first and third rectangle overlap each other.
解決
This problem was asked by Google.
What will this code print out?
def make_functions():
flist = []
for i in [1, 2, 3]:
def print_i():
print(i)
flist.append(print_i)
return flist
functions = make_functions()
for f in functions:
f()
How can we make it print out what we apparently want?
解決
This problem was asked by Google.
Given an array of elements, return the length of the longest subarray where all its elements are distinct.
For example, given the array [5, 1, 3, 5, 2, 3, 4, 1] , return 5 as the longest subarray of distinct elements is [5, 2, 3, 4, 1] .
解決
This problem was asked by Facebook.
Given a circular array, compute its maximum subarray sum in O(n) time.
For example, given [8, -1, 3, 4] , return 15 as we choose the numbers 3 , 4 , and 8 where the 8 is obtained from wrapping around.
Given [-4, 5, 1, 0] , return 6 as we choose the numbers 5 and 1 .
解決
This problem was asked by Stripe.
Given a collection of intervals, find the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping.
Intervals can "touch", such as [0, 1] and [1, 2] , but they won't be considered overlapping.
For example, given the intervals (7, 9), (2, 4), (5, 8) , return 1 as the last interval can be removed and the first two won't overlap.
The intervals are not necessarily sorted in any order.
解決
This problem was asked by Google.
You are given an array of nonnegative integers. Let's say you start at the beginning of the array and are trying to advance to the end. You can advance at most, the number of steps that you're currently on. Determine whether you can get to the end of the array.
For example, given the array [1, 3, 1, 2, 0, 1] , we can go from indices 0 -> 1 -> 3 -> 5 , so return true .
Given the array [1, 2, 1, 0, 0] , we can't reach the end, so return false .
解決
This problem was asked by Affirm.
Given a array of numbers representing the stock prices of a company in chronological order, write a function that calculates the maximum profit you could have made from buying and selling that stock. You're also given a number fee that represents a transaction fee for each buy and sell transaction.
You must buy before you can sell the stock, but you can make as many transactions as you like.
For example, given [1, 3, 2, 8, 4, 10] and fee = 2 , you should return 9 , since you could buy the stock at $1 , and sell at $8 , and then buy it at $4 and sell it at $10 . Since we did two transactions, there is a $4 fee, so we have 7 + 6 = 13 profit minus $4 of fees.
解決
This problem was asked by Facebook.
Suppose you are given two lists of n points, one list p1, p2, ..., pn on the line y = 0 and the other list q1, q2, ..., qn on the line y = 1 . Imagine a set of n line segments connecting each point pi to qi . Write an algorithm to determine how many pairs of the line segments intersect.
解決
This problem was asked by Google.
Let M be an N by N matrix in which every row and every column is sorted. No two elements of M are equal.
Given i1 , j1 , i2 , and j2 , compute the number of elements of M smaller than M[i1, j1] and larger than M[i2, j2] .
解決
This problem was asked by Apple.
Given the root of a binary tree, find the most frequent subtree sum. The subtree sum of a node is the sum of all values under a node, including the node itself.
For example, given the following tree:
5
/
2 -5
Return 2 as it occurs twice: once as the left leaf, and once as the sum of 2 + 5 - 5.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Google.
Given a set of distinct positive integers, find the largest subset such that every pair of elements in the subset (i, j) satisfies either i % j = 0 or j % i = 0 .
For example, given the set [3, 5, 10, 20, 21] , you should return [5, 10, 20] . Given [1, 3, 6, 24] , return [1, 3, 6, 24] .
解決
This problem was asked by Facebook.
Given a string of parentheses, find the balanced string that can be produced from it using the minimum number of insertions and deletions. If there are multiple solutions, return any of them.
For example, given "(()" , you could return "(())" . Given "))()(" , you could return "()()()()" .
解決
This problem was asked by Microsoft.
Let X be a set of n intervals on the real line. We say that a set of points P "stabs" X if every interval in X contains at least one point in P . Compute the smallest set of points that stabs X .
For example, given the intervals [(1, 4), (4, 5), (7, 9), (9, 12)] , you should return [4, 9] .
解決
This problem was asked by Google.
You are given an array of arrays of integers, where each array corresponds to a row in a triangle of numbers. For example, [[1], [2, 3], [1, 5, 1]] represents the triangle:
1
2 3
1 5 1
We define a path in the triangle to start at the top and go down one row at a time to an adjacent value, eventually ending with an entry on the bottom row. For example, 1 -> 3 -> 5 . The weight of the path is the sum of the entries.
Write a program that returns the weight of the maximum weight path.
解決
This problem was asked by Palantir.
Write a program that checks whether an integer is a palindrome. For example, 121 is a palindrome, as well as 888 . 678 is not a palindrome. Do not convert the integer into a string.
解決
This problem was asked by Uber.
Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand. Find the minimum element in O(log N) time. You may assume the array does not contain duplicates.
For example, given [5, 7, 10, 3, 4] , return 3 .
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by IBM.
Given an integer, find the next permutation of it in absolute order. For example, given 48975 , the next permutation would be 49578 .
解決
This problem was asked by Twitter.
A permutation can be specified by an array P , where P[i] represents the location of the element at i in the permutation. For example, [2, 1, 0] represents the permutation where elements at the index 0 and 2 are swapped.
Given an array and a permutation, apply the permutation to the array. For example, given the array ["a", "b", "c"] and the permutation [2, 1, 0] , return ["c", "b", "a"] .
解決
This problem was asked by Dropbox.
Given an undirected graph G , check whether it is bipartite. Recall that a graph is bipartite if its vertices can be divided into two independent sets, U and V , such that no edge connects vertices of the same set.
解決
This problem was asked by LinkedIn.
Given a linked list of numbers and a pivot k , partition the linked list so that all nodes less than k come before nodes greater than or equal to k .
For example, given the linked list 5 -> 1 -> 8 -> 0 -> 3 and k = 3 , the solution could be 1 -> 0 -> 5 -> 8 -> 3 .
解決
This problem was asked by YouTube.
Write a program that computes the length of the longest common subsequence of three given strings. For example, given "epidemiologist", "refrigeration", and "supercalifragilisticexpialodocious", it should return 5 , since the longest common subsequence is "eieio".
解決
This problem was asked by Apple.
A Collatz sequence in mathematics can be defined as follows. Starting with any positive integer:
n is even, the next number in the sequence is n / 2n is odd, the next number in the sequence is 3n + 1 It is conjectured that every such sequence eventually reaches the number 1 . Test this conjecture. Bonus: What input n <= 1000000 gives the longest sequence?
解決
This problem was asked by Microsoft.
Given a string and a pattern, find the starting indices of all occurrences of the pattern in the string. For example, given the string "abracadabra" and the pattern "abr", you should return [0, 7] .
解決
This problem was asked by Dropbox.
Spreadsheets often use this alphabetical encoding for its columns: "A", "B", "C", ..., "AA", "AB", ..., "ZZ", "AAA", "AAB", ...
Given a column number, return its alphabetical column id. For example, given 1 , return "A". Given 27 , return "AA".
解決
This problem was asked by Snapchat.
Given a string of digits, generate all possible valid IP address combinations.
IP addresses must follow the format ABCD , where A , B , C , and D are numbers between 0 and 255 . Zero-prefixed numbers, such as 01 and 065 , are not allowed, except for 0 itself.
For example, given "2542540123", you should return ['254.25.40.123', '254.254.0.123'] .
解決
This problem was asked by Stripe.
Given an integer n , return the length of the longest consecutive run of 1 s in its binary representation.
For example, given 156 , you should return 3 .
解決
This problem was asked by Yelp.
The horizontal distance of a binary tree node describes how far left or right the node will be when the tree is printed out.
More rigorously, we can define it as follows:
0 .hd(parent) - 1 .hd(parent) + 1 . For example, for the following tree, hd(1) = -2 , and hd(6) = 0 .
5
/
3 7
/ /
1 4 6 9
/ /
0 8
The bottom view of a tree, then, consists of the lowest node at each horizontal distance. If there are two nodes at the same depth and horizontal distance, either is acceptable.
For this tree, for example, the bottom view could be [0, 1, 3, 6, 8, 9] .
Given the root to a binary tree, return its bottom view.
解決
This problem was asked by Facebook.
Given a number in Roman numeral format, convert it to decimal.
The values of Roman numerals are as follows:
{
'M': 1000,
'D': 500,
'C': 100,
'L': 50,
'X': 10,
'V': 5,
'I': 1
}
In addition, note that the Roman numeral system uses subtractive notation for numbers such as IV and XL .
For the input XIV , for instance, you should return 14 .
解決
This problem was asked by Oracle.
We say a number is sparse if there are no adjacent ones in its binary representation. For example, 21 ( 10101 ) is sparse, but 22 ( 10110 ) is not. For a given input N , find the smallest sparse number greater than or equal to N .
Do this in faster than O(N log N) time.
解決
This problem was asked by Yahoo.
Write an algorithm that computes the reversal of a directed graph. For example, if a graph consists of A -> B -> C , it should become A <- B <- C .
解決
This problem was asked by Salesforce.
Connect 4 is a game where opponents take turns dropping red or black discs into a 7 x 6 vertically suspended grid. The game ends either when one player creates a line of four consecutive discs of their color (horizontally, vertically, or diagonally), or when there are no more spots left in the grid.
Design and implement Connect 4.
解決
This problem was asked by Square.
In front of you is a row of N coins, with values v_1, v_2, ..., v_n .
You are asked to play the following game. You and an opponent take turns choosing either the first or last coin from the row, removing it from the row, and receiving the value of the coin.
Write a program that returns the maximum amount of money you can win with certainty, if you move first, assuming your opponent plays optimally.
解決
This problem was asked by Zillow.
Let's define a "sevenish" number to be one which is either a power of 7 , or the sum of unique powers of 7 . The first few sevenish numbers are 1, 7, 8, 49 , and so on. Create an algorithm to find the n th sevenish number.
解決
This problem was asked by Quora.
Given an absolute pathname that may have . or .. as part of it, return the shortest standardized path.
For example, given /usr/bin/../bin/./scripts/../ , return /usr/bin/ .
解決
This problem was asked by Palantir.
Typically, an implementation of in-order traversal of a binary tree has O(h) space complexity, where h is the height of the tree. Write a program to compute the in-order traversal of a binary tree using O(1) space.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Bloomberg.
There are N prisoners standing in a circle, waiting to be executed. The executions are carried out starting with the k th person, and removing every successive k th person going clockwise until there is no one left.
Given N and k , write an algorithm to determine where a prisoner should stand in order to be the last survivor.
For example, if N = 5 and k = 2 , the order of executions would be [2, 4, 1, 5, 3] , so you should return 3 .
Bonus: Find an O(log N) solution if k = 2 .
解決
This problem was asked by Airbnb.
You come across a dictionary of sorted words in a language you've never seen before. Write a program that returns the correct order of letters in this language.
For example, given ['xww', 'wxyz', 'wxyw', 'ywx', 'ywz'] , you should return ['x', 'z', 'w', 'y'] .
解決
This problem was asked by Facebook.
Boggle is a game played on a 4 x 4 grid of letters. The goal is to find as many words as possible that can be formed by a sequence of adjacent letters in the grid, using each cell at most once. Given a game board and a dictionary of valid words, implement a Boggle solver.
解決
This problem was asked by Twitter.
Given a list of numbers, create an algorithm that arranges them in order to form the largest possible integer. For example, given [10, 7, 76, 415] , you should return 77641510 .
解決
This problem was asked by Flipkart.
Snakes and Ladders is a game played on a 10 x 10 board, the goal of which is get from square 1 to square 100 . On each turn players will roll a six-sided die and move forward a number of spaces equal to the result. If they land on a square that represents a snake or ladder, they will be transported ahead or behind, respectively, to a new square.
Find the smallest number of turns it takes to play snakes and ladders.
For convenience, here are the squares representing snakes and ladders, and their outcomes:
snakes = {16: 6, 48: 26, 49: 11, 56: 53, 62: 19, 64: 60, 87: 24, 93: 73, 95: 75, 98: 78}
ladders = {1: 38, 4: 14, 9: 31, 21: 42, 28: 84, 36: 44, 51: 67, 71: 91, 80: 100}
解決
This problem was asked by Goldman Sachs.
You are given N identical eggs and access to a building with k floors. Your task is to find the lowest floor that will cause an egg to break, if dropped from that floor. Once an egg breaks, it cannot be dropped again. If an egg breaks when dropped from the x th floor, you can assume it will also break when dropped from any floor greater than x .
Write an algorithm that finds the minimum number of trial drops it will take, in the worst case, to identify this floor.
For example, if N = 1 and k = 5 , we will need to try dropping the egg at every floor, beginning with the first, until we reach the fifth floor, so our solution will be 5 .
解決
This problem was asked by IBM.
Given a string with repeated characters, rearrange the string so that no two adjacent characters are the same. If this is not possible, return None.
For example, given "aaabbc", you could return "ababac". Given "aaab", return None.
解決
This problem was asked by Google.
Implement a PrefixMapSum class with the following methods:
insert(key: str, value: int) : Set a given key's value in the map. If the key already exists, overwrite the value. sum(prefix: str) : Return the sum of all values of keys that begin with a given prefix. For example, you should be able to run the following code:
mapsum.insert("columnar", 3)
assert mapsum.sum("col") == 3
mapsum.insert("column", 2)
assert mapsum.sum("col") == 5
解決
This problem was asked by Apple.
Implement the function fib(n) , which returns the nth number in the Fibonacci sequence, using only O(1) space.
解決
This problem was asked by Microsoft.
Recall that the minimum spanning tree is the subset of edges of a tree that connect all its vertices with the smallest possible total edge weight. Given an undirected graph with weighted edges, compute the maximum weight spanning tree.
解決
This problem was asked by Facebook.
Given an array of numbers of length N , find both the minimum and maximum using less than 2 * (N - 2) comparisons.
解決
This problem was asked by Nvidia.
You are given a list of N points (x1, y1), (x2, y2), ..., (xN, yN) representing a polygon. You can assume these points are given in order; that is, you can construct the polygon by connecting point 1 to point 2, point 2 to point 3, and so on, finally looping around to connect point N to point 1.
Determine if a new point p lies inside this polygon. (If p is on the boundary of the polygon, you should return False).
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by MIT.
Blackjack is a two player card game whose rules are as follows:
For this problem, cards values are counted as follows: each card between 2 and 10 counts as their face value, face cards count as 10, and aces count as 1.
Given perfect knowledge of the sequence of cards in the deck, implement a blackjack solver that maximizes the player's score (that is, wins minus losses).
解決
This problem was asked by Uber.
One way to unlock an Android phone is through a pattern of swipes across a 1-9 keypad.
For a pattern to be valid, it must satisfy the following:
All of its keys must be distinct. It must not connect two keys by jumping over a third key, unless that key has already been used. For example, 4 - 2 - 1 - 7 is a valid pattern, whereas 2 - 1 - 7 is not.
Find the total number of valid unlock patterns of length N, where 1 <= N <= 9 .
解決
This problem was asked by Spotify.
There are N couples sitting in a row of length 2 * N . They are currently ordered randomly, but would like to rearrange themselves so that each couple's partners can sit side by side. What is the minimum number of swaps necessary for this to happen?
解決
This problem was asked by Palantir.
In academia, the h-index is a metric used to calculate the impact of a researcher's papers. It is calculated as follows:
A researcher has index h if at least h of her N papers have h citations each. If there are multiple h satisfying this formula, the maximum is chosen.
For example, suppose N = 5 , and the respective citations of each paper are [4, 3, 0, 1, 5] . Then the h-index would be 3 , since the researcher has 3 papers with at least 3 citations.
Given a list of paper citations of a researcher, calculate their h-index.
解決
This problem was asked by Twitter.
You are given an array of length 24, where each element represents the number of new subscribers during the corresponding hour. Implement a data structure that efficiently supports the following:
update(hour: int, value: int) : Increment the element at index hour by value.query(start: int, end: int) : Retrieve the number of subscribers that have signed up between start and end (inclusive). You can assume that all values get cleared at the end of the day, and that you will not be asked for start and end values that wrap around midnight.解決
This problem was asked by Etsy.
Given an array of numbers N and an integer k , your task is to split N into k partitions such that the maximum sum of any partition is minimized. Return this sum.
For example, given N = [5, 1, 2, 7, 3, 4] and k = 3 , you should return 8 , since the optimal partition is [5, 1, 2], [7], [3, 4] 。
解決
This problem was asked by Square.
The Sieve of Eratosthenes is an algorithm used to generate all prime numbers smaller than N. The method is to take increasingly larger prime numbers, and mark their multiples as composite.
For example, to find all primes less than 100, we would first mark [4, 6, 8, ...] (multiples of two), then [6, 9, 12, ...] (multiples of three),等々。 Once we have done this for all primes less than N , the unmarked numbers that remain will be prime.
Implement this algorithm.
Bonus: Create a generator that produces primes indefinitely (that is, without taking N as an input).
解決
This problem was asked by Yelp.
You are given an array of integers, where each element represents the maximum number of steps that can be jumped going forward from that element. Write a function to return the minimum number of jumps you must take in order to get from the start to the end of the array.
For example, given [6, 2, 4, 0, 5, 1, 1, 4, 2, 9] , you should return 2 , as the optimal solution involves jumping from 6 to 5 , and then from 5 to 9 .
解決
This problem was asked by Dropbox.
Given a list of words, determine whether the words can be chained to form a circle. A word X can be placed in front of another word Y in a circle if the last character of X is same as the first character of Y .
For example, the words ['chair', 'height', 'racket', 'touch', 'tunic'] can form the following circle: chair -> racket -> touch -> height -> tunic -> chair .
解決
This problem was asked by PayPal.
Given a binary tree, determine whether or not it is height-balanced. A height-balanced binary tree can be defined as one in which the heights of the two subtrees of any node never differ by more than one.
解決
This problem was asked by Nvidia.
Find the maximum of two numbers without using any if-else statements, branching, or direct comparisons.
解決
This problem was asked by Salesforce.
Given an array of integers, find the maximum XOR of any two elements.
解決
This problem was asked by Google.
A cryptarithmetic puzzle is a mathematical game where the digits of some numbers are represented by letters. Each letter represents a unique digit.
For example, a puzzle of the form:
SEND
+ MORE
--------
MONEY
may have the solution:
{'S': 9, 'E': 5, 'N': 6, 'D': 7, 'M': 1, 'O': 0, 'R': 8, 'Y': 2}
Given a three-word puzzle like the one above, create an algorithm that finds a solution.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Palantir.
The ancient Egyptians used to express fractions as a sum of several terms where each numerator is one. For example, 4 / 13 can be represented as 1 / (4 + 1 / (18 + (1 / 468))) .
Create an algorithm to turn an ordinary fraction a / b , where a < b , into an Egyptian fraction.
解決
This problem was asked by PayPal.
Given a string and a number of lines k , print the string in zigzag form. In zigzag, characters are printed out diagonally from top left to bottom right until reaching the kth line, then back up to top right, and so on.
For example, given the sentence "thisisazigzag" and k = 4 , you should print:
t a g
h s z a
i i i z
s g
解決
This problem was asked by Yahoo.
Recall that a full binary tree is one in which each node is either a leaf node, or has two children. Given a binary tree, convert it to a full one by removing nodes with only one child.
For example, given the following tree:
a
/
b c
/
d e
/
f g h
You should convert it to:
a
/
f e
/
g h
解決
This problem was asked by Microsoft.
The transitive closure of a graph is a measure of which vertices are reachable from other vertices. It can be represented as a matrix M , where M[i][j] == 1 if there is a path between vertices i and j , and otherwise 0 .
For example, suppose we are given the following graph in adjacency list form:
graph = [
[0, 1, 3],
[1, 2],
[2],
[3]
]
The transitive closure of this graph would be:
[1, 1, 1, 1]
[0, 1, 1, 0]
[0, 0, 1, 0]
[0, 0, 0, 1]
Given a graph, find its transitive closure.
解決
This problem was asked by Fitbit.
Given a linked list, rearrange the node values such that they appear in alternating low -> high -> low -> high ... form. For example, given 1 -> 2 -> 3 -> 4 -> 5 , you should return 1 -> 3 -> 2 -> 5 -> 4 .
解決
This problem was asked by WhatsApp.
Given an array of integers out of order, determine the bounds of the smallest window that must be sorted in order for the entire array to be sorted. For example, given [3, 7, 5, 6, 9] , you should return (1, 3) .
解決
This problem was asked by Morgan Stanley.
In Ancient Greece, it was common to write text with the first line going left to right, the second line going right to left, and continuing to go back and forth. This style was called "boustrophedon".
Given a binary tree, write an algorithm to print the nodes in boustrophedon order.
For example, given the following tree:
1
/
2 3
/ /
4 5 6 7
You should return [1, 3, 2, 4, 5, 6, 7] .
解決
This problem was asked by Two Sigma.
Ghost is a two-person word game where players alternate appending letters to a word. The first person who spells out a word, or creates a prefix for which there is no possible continuation, loses. Here is a sample game:
Player 1: g
Player 2: h
Player 1: o
Player 2: s
Player 1: t [loses]
Given a dictionary of words, determine the letters the first player should start with, such that with optimal play they cannot lose.
For example, if the dictionary is ["cat", "calf", "dog", "bear"] , the only winning start letter would be b.
解決
This problem was asked by Pinterest.
The sequence [0, 1, ..., N] has been jumbled, and the only clue you have for its order is an array representing whether each number is larger or smaller than the last. Given this information, reconstruct an array that is consistent with it. For example, given [None, +, +, -, +] , you could return [1, 2, 3, 0, 4] .
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Mozilla.
A bridge in a connected (undirected) graph is an edge that, if removed, causes the graph to become disconnected. Find all the bridges in a graph.
解決
This problem was asked by Nest.
Create a basic sentence checker that takes in a stream of characters and determines whether they form valid sentences. If a sentence is valid, the program should print it out.
We can consider a sentence valid if it conforms to the following rules:
(,,;,:) or terminal marks (.,?,!,‽) .解決
This problem was asked by LinkedIn.
Given a set of characters C and an integer k , a De Bruijn sequence is a cyclic sequence in which every possible k -length string of characters in C occurs exactly once.
For example, suppose C = {0, 1} and k = 3 . Then our sequence should contain the substrings {'000', '001', '010', '011', '100', '101', '110', '111'} , and one possible solution would be 00010111 .
Create an algorithm that finds a De Bruijn sequence.
解決
This problem was asked by Atlassian.
MegaCorp wants to give bonuses to its employees based on how many lines of codes they have written. They would like to give the smallest positive amount to each worker consistent with the constraint that if a developer has written more lines of code than their neighbor, they should receive more money.
Given an array representing a line of seats of employees at MegaCorp, determine how much each one should get paid.
For example, given [10, 40, 200, 1000, 60, 30] , you should return [1, 2, 3, 4, 2, 1] .
解決
This problem was asked by Pivotal.
A step word is formed by taking a given word, adding a letter, and anagramming the result. For example, starting with the word "APPLE", you can add an "A" and anagram to get "APPEAL".
Given a dictionary of words and an input word, create a function that returns all valid step words.
解決
This problem was asked by Oracle.
You are presented with an 8 by 8 matrix representing the positions of pieces on a chess board. The only pieces on the board are the black king and various white pieces. Given this matrix, determine whether the king is in check.
For details on how each piece moves, see here.
For example, given the following matrix:
...K....
........
.B......
......P.
.......R
..N.....
........
.....Q..
You should return True , since the bishop is attacking the king diagonally.
解決
This problem was asked by Indeed.
Given a 32-bit positive integer N , determine whether it is a power of four in faster than O(log N) time.
解決
This problem was asked by Microsoft.
You are given an string representing the initial conditions of some dominoes. Each element can take one of three values:
L , meaning the domino has just been pushed to the left,R , meaning the domino has just been pushed to the right, or. , meaning the domino is standing still.Determine the orientation of each tile when the dominoes stop falling. Note that if a domino receives a force from the left and right side simultaneously, it will remain upright.
For example, given the string .LR...L , you should return LL.RRRLLL .
Given the string ..R...LL , you should return ..RR.LLLL .
解決
This problem was asked by Twitter.
A network consists of nodes labeled 0 to N . You are given a list of edges (a, b, t) , describing the time t it takes for a message to be sent from node a to node b . Whenever a node receives a message, it immediately passes the message on to a neighboring node, if possible.
Assuming all nodes are connected, determine how long it will take for every node to receive a message that begins at node 0 .
For example, given N = 5 , and the following edges:
edges = [
(0, 1, 5),
(0, 2, 3),
(0, 5, 4),
(1, 3, 8),
(2, 3, 1),
(3, 5, 10),
(3, 4, 5)
]
You should return 9 , because propagating the message from 0 -> 2 -> 3 -> 4 will take that much time.
解決
This problem was asked by Netflix.
Given a sorted list of integers of length N , determine if an element x is in the list without performing any multiplication, division, or bit-shift operations.
Do this in O(log N) time.
解決
This problem was asked by Spotify.
Write a function, throw_dice(N, faces, total) , that determines how many ways it is possible to throw N dice with some number of faces each to get a specific total.
For example, throw_dice(3, 6, 7) should equal 15 .
解決
This problem was asked by Apple.
A fixed point in an array is an element whose value is equal to its index. Given a sorted array of distinct elements, return a fixed point, if one exists. Otherwise, return False .
For example, given [-6, 0, 2, 40] , you should return 2 . Given [1, 5, 7, 8] , you should return False .
解決
This problem was asked by Facebook.
Given a string consisting of parentheses, single digits, and positive and negative signs, convert the string into a mathematical expression to obtain the answer.
Don't use eval or a similar built-in parser.
For example, given '-1 + (2 + 3)' , you should return 4 .
解決
This problem was asked by Epic.
The "look and say" sequence is defined as follows: beginning with the term 1 , each subsequent term visually describes the digits appearing in the previous term. The first few terms are as follows:
1
11
21
1211
111221
As an example, the fourth term is 1211 , since the third term consists of one 2 and one 1 .
Given an integer N , print the Nth term of this sequence.
解決
This problem was asked by Dropbox.
Implement an efficient string matching algorithm.
That is, given a string of length N and a pattern of length k , write a program that searches for the pattern in the string with less than O(N * k) worst-case time complexity.
If the pattern is found, return the start index of its location. If not, return False .
解決
This problem was asked by Google.
UTF-8 is a character encoding that maps each symbol to one, two, three, or four bytes.
For example, the Euro sign, € , corresponds to the three bytes 11100010 10000010 10101100 . The rules for mapping characters are as follows:
n -byte character, the first byte starts with n ones and a zero. The other n - 1 bytes all start with 10 . Visually, this can be represented as follows. Bytes | Byte format
-----------------------------------------------
1 | 0xxxxxxx
2 | 110xxxxx 10xxxxxx
3 | 1110xxxx 10xxxxxx 10xxxxxx
4 | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
Write a program that takes in an array of integers representing byte values, and returns whether it is a valid UTF-8 encoding.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Twitter.
A classroom consists of N students, whose friendships can be represented in an adjacency list. For example, the following descibes a situation where 0 is friends with 1 and 2 , 3 is friends with 6 , and so on.
{
0: [1, 2],
1: [0, 5],
2: [0],
3: [6],
4: [],
5: [1],
6: [3]
}
Each student can be placed in a friend group, which can be defined as the transitive closure of that student's friendship relations. In other words, this is the smallest set such that no student in the group has any friends outside this group. For the example above, the friend groups would be {0, 1, 2, 5}, {3, 6}, {4} .
Given a friendship list such as the one above, determine the number of friend groups in the class.
解決
This problem was asked by Pandora.
Given an undirected graph, determine if it contains a cycle.
解決
This problem was asked by LinkedIn.
A wall consists of several rows of bricks of various integer lengths and uniform height. Your goal is to find a vertical line going from the top to the bottom of the wall that cuts through the fewest number of bricks. If the line goes through the edge between two bricks, this does not count as a cut.
For example, suppose the input is as follows, where values in each row represent the lengths of bricks in that row:
[[3, 5, 1, 1],
[2, 3, 3, 2],
[5, 5],
[4, 4, 2],
[1, 3, 3, 3],
[1, 1, 6, 1, 1]]
The best we can we do here is to draw a line after the eighth brick, which will only require cutting through the bricks in the third and fifth row.
Given an input consisting of brick lengths for each row such as the one above, return the fewest number of bricks that must be cut to create a vertical line.
解決
This problem was asked by Netflix.
Given an array of integers, determine whether it contains a Pythagorean triplet. Recall that a Pythogorean triplet (a, b, c) is defined by the equation a^2 + b^2 = c^2 .
解決
This problem was asked by Google.
A regular number in mathematics is defined as one which evenly divides some power of 60 . Equivalently, we can say that a regular number is one whose only prime divisors are 2 , 3 , and 5 .
These numbers have had many applications, from helping ancient Babylonians keep time to tuning instruments according to the diatonic scale.
Given an integer N , write a program that returns, in order, the first N regular numbers.
解決
This problem was asked by Yext.
Two nodes in a binary tree can be called cousins if they are on the same level of the tree but have different parents. For example, in the following diagram 4 and 6 are cousins.
1
/
2 3
/
4 5 6
Given a binary tree and a particular node, find all cousins of that node.
解決
This problem was asked by Mailchimp.
You are given an array representing the heights of neighboring buildings on a city street, from east to west. The city assessor would like you to write an algorithm that returns how many of these buildings have a view of the setting sun, in order to properly value the street.
For example, given the array [3, 7, 8, 3, 6, 1] , you should return 3 , since the top floors of the buildings with heights 8 , 6 , and 1 all have an unobstructed view to the west.
Can you do this using just one forward pass through the array?
解決
This problem was asked by VMware.
The skyline of a city is composed of several buildings of various widths and heights, possibly overlapping one another when viewed from a distance. We can represent the buildings using an array of (left, right, height) tuples, which tell us where on an imaginary x -axis a building begins and ends, and how tall it is. The skyline itself can be described by a list of (x, height) tuples, giving the locations at which the height visible to a distant observer changes, and each new height.
Given an array of buildings as described above, create a function that returns the skyline.
For example, suppose the input consists of the buildings [(0, 15, 3), (4, 11, 5), (19, 23, 4)] . In aggregate, these buildings would create a skyline that looks like the one below.
______
| | ___
___| |___ | |
| | B | | | C |
| A | | A | | |
| | | | | |
------------------------
As a result, your function should return [(0, 3), (4, 5), (11, 3), (15, 0), (19, 4), (23, 0)] .
解決
This problem was asked by Quora.
You are given a list of (website, user) pairs that represent users visiting websites. Come up with a program that identifies the top k pairs of websites with the greatest similarity.
For example, suppose k = 1 , and the list of tuples is:
[('a', 1), ('a', 3), ('a', 5),
('b', 2), ('b', 6),
('c', 1), ('c', 2), ('c', 3), ('c', 4), ('c', 5),
('d', 4), ('d', 5), ('d', 6), ('d', 7),
('e', 1), ('e', 3), ('e', 5), ('e', 6)]
Then a reasonable similarity metric would most likely conclude that a and e are the most similar, so your program should return [('a', 'e')] .
解決
This problem was asked by Salesforce.
The number 6174 is known as Kaprekar's contant, after the mathematician who discovered an associated property: for all four-digit numbers with at least two distinct digits, repeatedly applying a simple procedure eventually results in this value.手順は次のとおりです。
For a given input x , create two new numbers that consist of the digits in x in ascending and descending order. Subtract the smaller number from the larger number. For example, this algorithm terminates in three steps when starting from 1234 :
4321 - 1234 = 3087
8730 - 0378 = 8352
8532 - 2358 = 6174
Write a function that returns how many steps this will take for a given input N .
解決
This problem was asked by Google.
The game of Nim is played as follows. Starting with three heaps, each containing a variable number of items, two players take turns removing one or more items from a single pile. The player who eventually is forced to take the last stone loses. For example, if the initial heap sizes are 3, 4, and 5, a game could be played as shown below:
| a | b | c |
|---|---|---|
| 3 | 4 | 5 |
| 3 | 1 | 5 |
| 3 | 1 | 3 |
| 0 | 1 | 3 |
| 0 | 1 | 0 |
| 0 | 0 | 0 |
In other words, to start, the first player takes three items from pile B . The second player responds by removing two stones from pile C . The game continues in this way until player one takes last stone and loses.
Given a list of non-zero starting values [a, b, c] , and assuming optimal play, determine whether the first player has a forced win.
解決
This problem was asked by Facebook.
On a mysterious island there are creatures known as Quxes which come in three colors: red, green, and blue. One power of the Qux is that if two of them are standing next to each other, they can transform into a single creature of the third color.
Given N Quxes standing in a line, determine the smallest number of them remaining after any possible sequence of such transformations.
For example, given the input ['R', 'G', 'B', 'G', 'B'] , it is possible to end up with a single Qux through the following steps:
Arrangement | Change
----------------------------------------
['R', 'G', 'B', 'G', 'B'] | (R, G) -> B
['B', 'B', 'G', 'B'] | (B, G) -> R
['B', 'R', 'B'] | (R, B) -> G
['B', 'G'] | (B, G) -> R
['R'] |
解決
This problem was asked by Glassdoor.
An imminent hurricane threatens the coastal town of Codeville. If at most two people can fit in a rescue boat, and the maximum weight limit for a given boat is k , determine how many boats will be needed to save everyone.
For example, given a population with weights [100, 200, 150, 80] and a boat limit of 200 , the smallest number of boats required will be three.
解決
This problem was asked by Twitter.
A teacher must divide a class of students into two teams to play dodgeball. Unfortunately, not all the kids get along, and several refuse to be put on the same team as that of their enemies.
Given an adjacency list of students and their enemies, write an algorithm that finds a satisfactory pair of teams, or returns False if none exists.
For example, given the following enemy graph you should return the teams {0, 1, 4, 5} and {2, 3} .
students = {
0: [3],
1: [2],
2: [1, 4],
3: [0, 4, 5],
4: [2, 3],
5: [3]
}
On the other hand, given the input below, you should return False .
students = {
0: [3],
1: [2],
2: [1, 3, 4],
3: [0, 2, 4, 5],
4: [2, 3],
5: [3]
}
解決
This problem was asked by Uber.
You have N stones in a row, and would like to create from them a pyramid. This pyramid should be constructed such that the height of each stone increases by one until reaching the tallest stone, after which the heights decrease by one. In addition, the start and end stones of the pyramid should each be one stone high.
You can change the height of any stone by paying a cost of 1 unit to lower its height by 1 , as many times as necessary. Given this information, determine the lowest cost method to produce this pyramid.
For example, given the stones [1, 1, 3, 3, 2, 1] , the optimal solution is to pay 2 to create [0, 1, 2, 3, 2, 1] .
解決
This problem was asked by Square.
A competitive runner would like to create a route that starts and ends at his house, with the condition that the route goes entirely uphill at first, and then entirely downhill.
Given a dictionary of places of the form {location: elevation} , and a dictionary mapping paths between some of these locations to their corresponding distances, find the length of the shortest route satisfying the condition above. Assume the runner's home is location 0 .
For example, suppose you are given the following input:
elevations = {0: 5, 1: 25, 2: 15, 3: 20, 4: 10}
paths = {
(0, 1): 10,
(0, 2): 8,
(0, 3): 15,
(1, 3): 12,
(2, 4): 10,
(3, 4): 5,
(3, 0): 17,
(4, 0): 10
}
In this case, the shortest valid path would be 0 -> 2 -> 4 -> 0 , with a distance of 28 .
解決
This problem was asked by Stitch Fix.
Pascal's triangle is a triangular array of integers constructed with the following formula:
The first row consists of the number 1. For each subsequent row, each element is the sum of the numbers directly above it, on either side. For example, here are the first few rows:
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
Given an input k , return the k th row of Pascal's triangle.
Bonus: Can you do this using only O(k) space?
解決
This problem was asked by Etsy.
Given a sorted array, convert it into a height-balanced binary search tree.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Google.
A girl is walking along an apple orchard with a bag in each hand. She likes to pick apples from each tree as she goes along, but is meticulous about not putting different kinds of apples in the same bag.
Given an input describing the types of apples she will pass on her path, in order, determine the length of the longest portion of her path that consists of just two types of apple trees.
For example, given the input [2, 1, 2, 3, 3, 1, 3, 5] , the longest portion will involve types 1 and 3 , with a length of four.
解決
This problem was asked by Samsung.
A group of houses is connected to the main water plant by means of a set of pipes. A house can either be connected by a set of pipes extending directly to the plant, or indirectly by a pipe to a nearby house which is otherwise connected.
For example, here is a possible configuration, where A, B, and C are houses, and arrows represent pipes: A <--> B <--> C <--> plant
Each pipe has an associated cost, which the utility company would like to minimize. Given an undirected graph of pipe connections, return the lowest cost configuration of pipes such that each house has access to water.
In the following setup, for example, we can remove all but the pipes from plant to A, plant to B, and B to C, for a total cost of 16.
pipes = {
'plant' : { 'A' : 1 , 'B' : 5 , 'C' : 20 },
'A' : { 'C' : 15 },
'B' : { 'C' : 10 },
'C' : {}
}解決
This problem was asked by Uber.
On election day, a voting machine writes data in the form (voter_id, candidate_id) to a text file. Write a program that reads this file as a stream and returns the top 3 candidates at any given time. If you find a voter voting more than once, report this as fraud.
解決
This problem was asked by Triplebyte.
Implement a data structure which carries out the following operations without resizing the underlying array:
add(value) : Add a value to the set of values.check(value) : Check whether a value is in the set.The check method may return occasional false positives (in other words, incorrectly identifying an element as part of the set), but should always correctly identify a true element.
解決
This problem was asked by Uber.
You are given a 2-d matrix where each cell consists of either / , , or an empty space. Write an algorithm that determines into how many regions the slashes divide the space.
For example, suppose the input for a three-by-six grid is the following:
/
/
/
Considering the edges of the matrix as boundaries, this divides the grid into three triangles, so you should return 3 .
解決
This problem was asked by Microsoft.
Given a clock time in hh:mm format, determine, to the nearest degree, the angle between the hour and the minute hands.
Bonus: When, during the course of a day, will the angle be zero?
解決
This problem was asked by Two Sigma.
A knight is placed on a given square on an 8 x 8 chessboard. It is then moved randomly several times, where each move is a standard knight move. If the knight jumps off the board at any point, however, it is not allowed to jump back on.
After k moves, what is the probability that the knight remains on the board?
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Palantir.
You are given a list of N numbers, in which each number is located at most k places away from its sorted position. For example, if k = 1 , a given element at index 4 might end up at indices 3 , 4 , or 5 .
Come up with an algorithm that sorts this list in O(N log k) time.
解決
This problem was asked by Oracle.
Given a binary search tree, find the floor and ceiling of a given integer. The floor is the highest element in the tree less than or equal to an integer, while the ceiling is the lowest element in the tree greater than or equal to an integer.
If either value does not exist, return None.
解決
This problem was asked by Quantcast.
You are presented with an array representing a Boolean expression. The elements are of two kinds:
T and F , representing the values True and False .& , | , and ^ , representing the bitwise operators for AND , OR , and XOR . Determine the number of ways to group the array elements using parentheses so that the entire expression evaluates to True .
For example, suppose the input is ['F', '|', 'T', '&', 'T'] . In this case, there are two acceptable groupings: (F | T) & T and F | (T & T) .
解決
This problem was asked by Walmart Labs.
There are M people sitting in a row of N seats, where M < N . Your task is to redistribute people such that there are no gaps between any of them, while keeping overall movement to a minimum.
For example, suppose you are faced with an input of [0, 1, 1, 0, 1, 0, 0, 0, 1] , where 0 represents an empty seat and 1 represents a person. In this case, one solution would be to place the person on the right in the fourth seat. We can consider the cost of a solution to be the sum of the absolute distance each person must move, so that the cost here would be 5 .
Given an input such as the one above, return the lowest possible cost of moving people to remove all gaps.
解決
This problem was asked by Pivotal.
Write an algorithm that finds the total number of set bits in all integers between 1 and N .
解決
This problem was asked by Sumo Logic.
Given an unsorted array, in which all elements are distinct, find a "peak" element in O(log N) time.
An element is considered a peak if it is greater than both its left and right neighbors. It is guaranteed that the first and last elements are lower than all others.
解決
This problem was asked by Wayfair.
You are given a 2 x N board, and instructed to completely cover the board with the following shapes:
2 x 1 rectangles. For example, if N = 4 , here is one possible configuration, where A is a domino, and B and C are trominoes.
A B B C
A B C C
Given an integer N, determine in how many ways this task is possible.
解決
This problem was asked by Citrix.
You are given a circular lock with three wheels, each of which display the numbers 0 through 9 in order. Each of these wheels rotate clockwise and counterclockwise.
In addition, the lock has a certain number of "dead ends", meaning that if you turn the wheels to one of these combinations, the lock becomes stuck in that state and cannot be opened.
Let us consider a "move" to be a rotation of a single wheel by one digit, in either direction. Given a lock initially set to 000 , a target combination, and a list of dead ends, write a function that returns the minimum number of moves required to reach the target state, or None if this is impossible.
解決
This problem was asked by Spotify.
You are the technical director of WSPT radio, serving listeners nationwide. For simplicity's sake we can consider each listener to live along a horizontal line stretching from 0 (west) to 1000 (east).
Given a list of N listeners, and a list of M radio towers, each placed at various locations along this line, determine what the minimum broadcast range would have to be in order for each listener's home to be covered.
For example, suppose listeners = [1, 5, 11, 20] , and towers = [4, 8, 15] . In this case the minimum range would be 5 , since that would be required for the tower at position 15 to reach the listener at position 20 .
解決
This problem was asked by Google.
In linear algebra, a Toeplitz matrix is one in which the elements on any given diagonal from top left to bottom right are identical.
Here is an example:
1 2 3 4 8
5 1 2 3 4
4 5 1 2 3
7 4 5 1 2
Write a program to determine whether a given input is a Toeplitz matrix.
解決
This problem was asked by Snapchat.
You are given an array of length N , where each element i represents the number of ways we can produce i units of change. For example, [1, 0, 1, 1, 2] would indicate that there is only one way to make 0 , 2 , or 3 units, and two ways of making 4 units.
Given such an array, determine the denominations that must be in use. In the case above, for example, there must be coins with value 2 , 3 , and 4 .
解決
This problem was asked by Yahoo.
Write a function that returns the bitwise AND of all integers between M and N , inclusive.
解決
This problem was asked by Apple.
You are going on a road trip, and would like to create a suitable music playlist. The trip will require N songs, though you only have M songs downloaded, where M < N . A valid playlist should select each song at least once, and guarantee a buffer of B songs between repeats.
Given N , M , and B , determine the number of valid playlists.
解決
This problem was asked by Airbnb.
An 8-puzzle is a game played on a 3 x 3 board of tiles, with the ninth tile missing. The remaining tiles are labeled 1 through 8 but shuffled randomly. Tiles may slide horizontally or vertically into an empty space, but may not be removed from the board.
Design a class to represent the board, and find a series of steps to bring the board to the state [[1, 2, 3], [4, 5, 6], [7, 8, None]] .
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by PagerDuty.
Given a positive integer N , find the smallest number of steps it will take to reach 1 .
There are two kinds of permitted steps:
N to N - 1 .a * b = N , you may decrement N to the larger of a and b . For example, given 100 , you can reach 1 in five steps with the following route: 100 -> 10 -> 9 -> 3 -> 2 -> 1 .
解決
This problem was asked by Flipkart.
Starting from 0 on a number line, you would like to make a series of jumps that lead to the integer N .
On the i th jump, you may move exactly i places to the left or right.
Find a path with the fewest number of jumps required to get from 0 to N .
解決
This problem was asked by Dropbox.
Create an algorithm to efficiently compute the approximate median of a list of numbers.
More precisely, given an unordered list of N numbers, find an element whose rank is between N / 4 and 3 * N / 4 , with a high level of certainty, in less than O(N) time.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Jane Street.
The United States uses the imperial system of weights and measures, which means that there are many different, seemingly arbitrary units to measure distance. There are 12 inches in a foot, 3 feet in a yard, 22 yards in a chain, and so on.
Create a data structure that can efficiently convert a certain quantity of one unit to the correct amount of any other unit. You should also allow for additional units to be added to the system.
解決
This problem was asked by Netflix.
A Cartesian tree with sequence S is a binary tree defined by the following two properties:
It is heap-ordered, so that each parent value is strictly less than that of its children. An in-order traversal of the tree produces nodes with values that correspond exactly to S . For example, given the sequence [3, 2, 6, 1, 9] , the resulting Cartesian tree would be:
1
/
2 9
/
3 6
Given a sequence S, construct the corresponding Cartesian tree.
解決
This problem was asked by Salesforce.
Write a program to merge two binary trees. Each node in the new tree should hold a value equal to the sum of the values of the corresponding nodes of the input trees.
If only one input tree has a node in a given position, the corresponding node in the new tree should match that input node.
解決
This problem was asked by Facebook.
In chess, the Elo rating system is used to calculate player strengths based on game results.
A simplified description of the Elo system is as follows. Every player begins at the same score. For each subsequent game, the loser transfers some points to the winner, where the amount of points transferred depends on how unlikely the win is. For example, a 1200-ranked player should gain much more points for beating a 2000-ranked player than for beating a 1300-ranked player.
Implement this system.
解決
THE PROBLEM & THE SOLUTION WAS TAKEN DOWN DUE TO AMAZON'S COPYRIGHTS INFRINGEMENT
This problem was asked by Dropbox.
A Boolean formula can be said to be satisfiable if there is a way to assign truth values to each variable such that the entire formula evaluates to true.
For example, suppose we have the following formula, where the symbol ¬ is used to denote negation:
(¬c OR b) AND (b OR c) AND (¬b OR c) AND (¬c OR ¬a)
One way to satisfy this formula would be to let a = False , b = True , and c = True .
This type of formula, with AND statements joining tuples containing exactly one OR, is known as 2-CNF.
Given a 2-CNF formula, find a way to assign truth values to satisfy it, or return False if this is impossible.
解決
This problem was asked by LinkedIn.
You are given a string consisting of the letters x and y , such as xyxxxyxyy . In addition, you have an operation called flip, which changes a single x to y or vice versa.
Determine how many times you would need to apply this operation to ensure that all x 's come before all y 's. In the preceding example, it suffices to flip the second and sixth characters, so you should return 2 .
解決
This problem was asked by Jane Street.
Given integers M and N , write a program that counts how many positive integer pairs (a, b) satisfy the following conditions:
a + b = M
a XOR b = N
解決
This problem was asked by Pinterest.
At a party, there is a single person who everyone knows, but who does not know anyone in return (the "celebrity"). To help figure out who this is, you have access to an O(1) method called knows(a, b) , which returns True if person a knows person b , else False .
Given a list of N people and the above operation, find a way to identify the celebrity in O(N) time.
解決
This problem was asked by Twitter.
The 24 game is played as follows. You are given a list of four integers, each between 1 and 9 , in a fixed order. By placing the operators + , - , * , and / between the numbers, and grouping them with parentheses, determine whether it is possible to reach the value 24 .
For example, given the input [5, 2, 7, 8] , you should return True, since (5 * 2 - 7) * 8 = 24 .
Write a function that plays the 24 game.
解決
This problem was asked by Google.
PageRank is an algorithm used by Google to rank the importance of different websites. While there have been changes over the years, the central idea is to assign each site a score based on the importance of other pages that link to that page.
More mathematically, suppose there are N sites, and each site i has a certain count Ci of outgoing links. Then the score for a particular site Sj is defined as :
score(Sj) = (1 - d) / N + d * (score(Sx) / Cx+ score(Sy) / Cy+ ... + score(Sz) / Cz))
Here, Sx, Sy, ..., Sz denote the scores of all the other sites that have outgoing links to Sj , and d is a damping factor, usually set to around 0.85 , used to model the probability that a user will stop searching 。
Given a directed graph of links between various websites, write a program that calculates each site's page rank.
解決
This problem was asked by Microsoft.
Write a program to determine how many distinct ways there are to create a max heap from a list of N given integers.
For example, if N = 3 , and our integers are [1, 2, 3] , there are two ways, shown below.
3 3
/ /
1 2 2 1
解決
This problem was asked by Apple.
Given a linked list, uniformly shuffle the nodes. What if we want to prioritize space over time?
解決
This problem was asked by Facebook.
Given an integer n , find the next biggest integer with the same number of 1 -bits on. For example, given the number 6 ( 0110 in binary), return 9 ( 1001 ).
解決
This problem was asked by Microsoft.
Given an array of numbers and a number k , determine if there are three entries in the array which add up to the specified number k . For example, given [20, 303, 3, 4, 25] and k = 49 , return true as 20 + 4 + 25 = 49 .
解決
This problem was asked by Google.
Given a set of points (x, y) on a 2D cartesian plane, find the two closest points. For example, given the points [(1, 1), (-1, -1), (3, 4), (6, 1), (-1, -6), (-4, -3)] , return [(-1, -1), (1, 1)] .
解決
This problem was asked by Google.
You are given an N by N matrix of random letters and a dictionary of words. Find the maximum number of words that can be packed on the board from the given dictionary.
A word is considered to be able to be packed on the board if:
For example, given the following dictionary:
{ 'eat', 'rain', 'in', 'rat' }
and matrix:
[['e', 'a', 'n'],
['t', 't', 'i'],
['a', 'r', 'a']]
Your function should return 3, since we can make the words 'eat', 'in', and 'rat' without them touching each other. We could have alternatively made 'eat' and 'rain', but that would be incorrect since that's only 2 words.
解決
This problem was asked by Stripe.
reduce (also known as fold ) is a function that takes in an array, a combining function, and an initial value and builds up a result by calling the combining function on each element of the array, left to right. For example, we can write sum() in terms of reduce:
def add ( a , b ):
return a + b def sum ( lst ):
return reduce ( lst , add , 0 )This should call add on the initial value with the first element of the array, and then the result of that with the second element of the array, and so on until we reach the end, when we return the sum of the array.
Implement your own version of reduce.
解決
This problem was asked by Google.
Given a binary search tree and a range [a, b] (inclusive), return the sum of the elements of the binary search tree within the range.
For example, given the following tree:
5
/
3 8
/ /
2 4 6 10
and the range [4, 9] , return 23 (5 + 4 + 6 + 8) .
解決
This problem was asked by Adobe.
You are given a tree with an even number of nodes. Consider each connection between a parent and child node to be an "edge". You would like to remove some of these edges, such that the disconnected subtrees that remain each have an even number of nodes.
For example, suppose your input was the following tree:
1
/
2 3
/
4 5
/ |
6 7 8
In this case, removing the edge (3, 4) satisfies our requirement.
Write a function that returns the maximum number of edges you can remove while still satisfying this requirement.
解決
This problem was asked by Google.
You are given a set of synonyms, such as (big, large) and (eat, consume) . Using this set, determine if two sentences with the same number of words are equivalent.
For example, the following two sentences are equivalent:
Note that the synonyms (a, b) and (a, c) do not necessarily imply (b, c) : consider the case of (coach, bus) and (coach, teacher) .
Follow-up: what if we can assume that (a, b) and (a, c) do in fact imply (b, c) ?
解決
This problem was asked by Airbnb.
You are given a huge list of airline ticket prices between different cities around the world on a given day. These are all direct flights. Each element in the list has the format (source_city, destination, price) .
Consider a user who is willing to take up to k connections from their origin city A to their destination B . Find the cheapest fare possible for this journey and print the itinerary for that journey.
For example, our traveler wants to go from JFK to LAX with up to 3 connections, and our input flights are as follows:
[
('JFK', 'ATL', 150),
('ATL', 'SFO', 400),
('ORD', 'LAX', 200),
('LAX', 'DFW', 80),
('JFK', 'HKG', 800),
('ATL', 'ORD', 90),
('JFK', 'LAX', 500),
]
Due to some improbably low flight prices, the cheapest itinerary would be JFK -> ATL -> ORD -> LAX, costing $440.
解決
This problem was asked by Yahoo.
You are given a string of length N and a parameter k . The string can be manipulated by taking one of the first k letters and moving it to the end.
Write a program to determine the lexicographically smallest string that can be created after an unlimited number of moves.
For example, suppose we are given the string daily and k = 1 . The best we can create in this case is ailyd .
解決
This problem was asked by Zillow.
A ternary search tree is a trie-like data structure where each node may have up to three children. Here is an example which represents the words code , cob , be , ax , war , and we .
c
/ |
b o w
/ | | |
a e d a
| / | |
x b e r e
The tree is structured according to the following rules:
For instance, since code is the first word inserted in the tree, and cob lexicographically precedes cod , cob is represented as a left child extending from cod .
Implement insertion and search functions for a ternary search tree.
解決
This problem was asked by Grammarly.
Soundex is an algorithm used to categorize phonetically, such that two names that sound alike but are spelled differently have the same representation.
Soundex maps every name to a string consisting of one letter and three numbers, like M460 .
One version of the algorithm is as follows:
ck -> c ).y , w , and h . b, f, p, v -> 1
c, g, j, k, q, s, x, z -> 2
d, t -> 3
l -> 4
m, n -> 5
r -> 6
If you don't have three numbers yet, append zeros until you do. Keep the first three numbers. Using this scheme, Jackson and Jaxen both map to J250 .
Implement Soundex.
解決
This problem was asked by Uber.
Write a program that determines the smallest number of perfect squares that sum up to N .
Here are a few examples:
N = 4 , return 1 (4)N = 17 , return 2 (16 + 1)N = 18 , return 2 (9 + 9)解決
This problem was asked by Quora.
Word sense disambiguation is the problem of determining which sense a word takes on in a particular setting, if that word has multiple meanings. For example, in the sentence "I went to get money from the bank", bank probably means the place where people deposit money, not the land beside a river or lake.
Suppose you are given a list of meanings for several words, formatted like so:
{
"word_1": ["meaning one", "meaning two", ...],
...
"word_n": ["meaning one", "meaning two", ...]
}
Given a sentence, most of whose words are contained in the meaning list above, create an algorithm that determines the likely sense of each possibly ambiguous word.
解決
This problem was asked by Palantir.
A typical American-style crossword puzzle grid is an N x N matrix with black and white squares, which obeys the following rules:
The grid is rotationally symmetric (for example, the colors of the top left and bottom right squares must match). Write a program to determine whether a given matrix qualifies as a crossword grid.
解決
This problem was asked by Square.
You are given a histogram consisting of rectangles of different heights. These heights are represented in an input list, such that [1, 3, 2, 5] corresponds to the following diagram:
x
x
x x
x x x
x x x x
Determine the area of the largest rectangle that can be formed only from the bars of the histogram. For the diagram above, for example, this would be six, representing the 2 x 3 area at the bottom right.
解決
This problem was asked by Google.
Design a system to crawl and copy all of Wikipedia using a distributed network of machines.
More specifically, suppose your server has access to a set of client machines. Your client machines can execute code you have written to access Wikipedia pages, download and parse their data, and write the results to a database.
Some questions you may want to consider as part of your solution are:
解決
This problem was asked by Airbnb.
You are given an array X of floating-point numbers x1, x2, ... xn . These can be rounded up or down to create a corresponding array Y of integers y1, y2, ... yn .
Write an algorithm that finds an appropriate Y array with the following properties:
|x1- y1| + |x2- y2| + ... + |xn- yn| should be as small as possible. For example, suppose your input is [1.3, 2.3, 4.4] . In this case you cannot do better than [1, 2, 5] , which has an absolute difference of |1.3 - 1| + |2.3 - 2| + |4.4 - 5| = 1 .
解決
This problem was asked by Netflix.
Implement a queue using a set of fixed-length arrays.
The queue should support enqueue , dequeue , and get_size operations.
解決
This problem was asked by LinkedIn.
You are given a binary tree in a peculiar string representation. Each node is written in the form (lr) , where l corresponds to the left child and r corresponds to the right child.
If either l or r is null, it will be represented as a zero. Otherwise, it will be represented by a new (lr) pair.
Here are a few examples:
(00)((00)(00))((((00)0)0)0)Given this representation, determine the depth of the tree.
解決
This problem was asked by Dropbox.
Create a data structure that performs all the following operations in O(1) time:
plus : Add a key with value 1. If the key already exists, increment its value by one.minus : Decrement the value of a key. If the key's value is currently 1, remove it.get_max : Return a key with the highest value.get_min : Return a key with the lowest value.解決
This problem was asked by Slack.
You are given a string formed by concatenating several words corresponding to the integers zero through nine and then anagramming.
For example, the input could be 'niesevehrtfeev', which is an anagram of 'threefiveseven'. Note that there can be multiple instances of each integer.
Given this string, return the original integers in sorted order. In the example above, this would be 357 .
解決
This problem was asked by Spotify.
You have access to ranked lists of songs for various users. Each song is represented as an integer, and more preferred songs appear earlier in each list. For example, the list [4, 1, 7] indicates that a user likes song 4 the best, followed by songs 1 and 7 .
Given a set of these ranked lists, interleave them to create a playlist that satisfies everyone's priorities.
For example, suppose your input is {[1, 7, 3], [2, 1, 6, 7, 9], [3, 9, 5]} . In this case a satisfactory playlist could be [2, 1, 6, 7, 3, 9, 5] .
解決
This problem was asked by Facebook.
Mastermind is a two-player game in which the first player attempts to guess the secret code of the second. In this version, the code may be any six-digit number with all distinct digits.
Each turn the first player guesses some number, and the second player responds by saying how many digits in this number correctly matched their location in the secret code. For example, if the secret code were 123456 , then a guess of 175286 would score two, since 1 and 6 were correctly placed.
Write an algorithm which, given a sequence of guesses and their scores, determines whether there exists some secret code that could have produced them.
For example, for the following scores you should return True , since they correspond to the secret code 123456 : {175286: 2, 293416: 3, 654321: 0}
However, it is impossible for any key to result in the following scores, so in this case you should return False : {123456: 4, 345678: 4, 567890: 4}
解決
This problem was asked by Twitter.
A strobogrammatic number is a positive number that appears the same after being rotated 180 degrees. For example, 16891 is strobogrammatic.
Create a program that finds all strobogrammatic numbers with N digits.
解決
Write a function, add_subtract, which alternately adds and subtracts curried arguments. Here are some sample operations:
add_subtract(7) -> 7
add_subtract(1)(2)(3) -> 1 + 2 - 3 -> 0
add_subtract(-5)(10)(3)(9) -> -5 + 10 - 3 + 9 -> 11
解決
This problem was asked by Facebook.
Describe an algorithm to compute the longest increasing subsequence of an array of numbers in O(n log n) time.
解決
This problem was asked by Google.
A quack is a data structure combining properties of both stacks and queues. It can be viewed as a list of elements written left to right such that three operations are possible:
push(x) : add a new item x to the left end of the listpop() : remove and return the item on the left end of the listpull() : remove the item on the right end of the list. Implement a quack using three stacks and O(1) additional memory, so that the amortized time for any push, pop, or pull operation is O(1) .
解決
