Daily Coding Problem Solutions
1.0.0
该存储库包含Python中的每日编码问题解决方案。
安装第三方软件包，执行以下步骤：
cd Daily-Coding-Problem-Solutionspip install -r requirements.txt 在您贡献之前，请务必仔细阅读指南。
numpy和matplotlib仅用于演示目的，因此是可选的。给定数字列表，将任何两个总和返回到k。例如，给定[10、15、3、7]和17的k，返回true，因为10 + 7是17。
奖金：您可以一遍一次吗？
解决方案
Uber问这个问题。
给定一个整数数组，返回一个新数组，以使新数组的索引i处的每个元素都是原始数组中所有数字的乘积，除了i。
例如，如果我们的输入为[1、2、3、4、5]，则预期输出将为[120、60、40、30、24]。如果我们的输入为[3，2，1]，则预期输出将为[2，3，6]。
后续：如果您不能使用部门怎么办？
解决方案
Google问了这个问题。
鉴于二进制树的根，实现序列化（root），将树序列化到字符串中，并进行序列化（s），该序列将字符串恢复到树中。
解决方案
这个问题是通过条纹问的。
给定一个整数阵列，在线性时间和恒定空间中找到第一个缺失的正整数。换句话说，找到数组中不存在的最低正整数。阵列也可以包含重复项和负数。
例如，输入[3，4，-1，1]应给出2。输入[1，2，0]应给出3。
您可以修改输入阵列在场。
解决方案
简街问这个问题。
cons（a，b）构造一对，汽车（对）和CDR（Pair）返回该对的第一个和最后一个元素。例如，汽车（CONS（3，4））返回3，而CDR（CONS（3，4））返回4。
考虑到这种缺点的实施：
def cons ( a , b ):
return lambda f : f ( a , b )实施汽车和CDR。
解决方案
Google问了这个问题。
XOR链接列表是一个更有效的双重链接列表。它不是每个节点保存下一个和prev字段，而是保存一个名为“两个”字段，该字段是下一个节点和上一个节点的XOR。实现XOR链接列表；它具有一个添加（元素），该添加元素将元素添加到末端，而get（索引）则在索引处返回节点。
如果使用没有指针的语言（例如Python），则可以假定可以访问get_pointer和dereference_pointer函数，该功能可以在节点和内存地址之间转换。
解决方案
Facebook问这个问题。
给定映射a = 1，b = 2，... z = 26和一个编码的消息，计算可以解码的方法数。
例如，消息“ 111”将给出3，因为它可以被解码为“ AAA”，“ KA”和“ AK”。
您可以假设消息是可解码的。例如，不允许“ 001”。
解决方案
Google问了这个问题。
一棵Unival树（代表“通用值”）是一棵树，其中所有节点都具有相同的值。
鉴于二进制树的根，计算单个子树的数量。
例如，以下树有5个单一子树：
0
/
1 0
/
1 0
/
1 1
解决方案
Airbnb问了这个问题。
给定整数列表，编写一个函数，该函数返回最大的非贴上数字总和。数字可以为0或负数。
例如，[2，4，6，8]应该返回12，因为我们选择4和8。[5，1，1，5]应返回10，因为我们选择了5和5。
解决方案
这个问题是苹果问的。
实现一个函数f和整数n的作业调度程序，并在n毫秒之后调用f。
解决方案
Twitter问了这个问题。
实施自动完成系统。也就是说，给定查询字符串S和所有可能的查询字符串的集合，返回集合中的所有字符串作为前缀。
例如，给定查询字符串de和一组字符串[狗，鹿，交易]，返回[鹿，交易]。
提示：尝试将字典预处理成更有效的数据结构以加快查询。
解决方案
由于亚马逊的版权侵权，问题和解决方案被取消
由于亚马逊的版权侵权，问题和解决方案被取消
Google问了这个问题。
圆的面积定义为r^2。使用Monte Carlo方法将 pi估算到小数点小数点。
提示：一个圆的基本方程为x^2 + y^2 = r^2。
解决方案
Facebook问这个问题。
给定一系列元素流太大而无法存储在内存中，请从流中以均匀概率的方式选择一个随机元素。
解决方案
Twitter问了这个问题。
您运行一个电子商务网站，并希望在日志中记录最后的n订单ID。实施数据结构以实现这一目标，并使用以下API：
记录（order_id）：将order_id添加到log get_last（i）：从日志中获取最后一个元素。我可以保证比n小或等于n。您应该尽可能高效地在时间和空间上。
解决方案
Google问了这个问题。
假设我们以以下方式表示我们的文件系统：
字符串“ dir n tsubdir1 n tsubdir2 n t tfile.ext”表示：
dir
subdir1
subdir2
file.ext
目录DIR包含一个空的子目录subdir1和一个包含文件file.ext的子目录subdir2。
字符串“ dir n tsubdir1 n t t tfile1.ext n t t tsubsubdir1 n tsubdir2 n n n t t tsubsubdir2 n n n n n t t t t t t tfile2.ext”
dir
subdir1
file1.ext
subsubdir1
subdir2
subsubdir2
file2.ext
目录DIR包含两个子目录subdir1和subdir2。 subdir1包含一个文件file1.ext和一个空的第二级子目录subsubdir1。 subdir2包含一个二级子目录子dibdir2，其中包含一个文件file2.ext。
我们有兴趣找到文件系统中文件的最长（字符数）绝对路径。例如，在上面的第二个示例中，最长的绝对路径是“ dir/subdir2/subsubdir2/file2.ext”，其长度为32（不包括双引号）。
给定一个以上格式表示文件系统的字符串，将最长的绝对路径的长度返回到抽象文件系统中的文件。如果系统中没有文件，请返回0。
解决方案
Google问了这个问题。
给定一个整数和数字k，其中1 <= k <=阵列的长度，计算每个长度k的每个子阵列的最大值。
例如，给定数组= [10，5，2，7，8，7]和k = 3，我们应该得到：[10，7，8，8]，因为：
10 = max(10, 5, 2)
7 = max(5, 2, 7)
8 = max(2, 7, 8)
8 = max(7, 8, 7)
在o（n）时间和o（k）空间中执行此操作。您可以修改输入阵列在场，而无需存储结果。您可以在计算它们时只需将它们打印出来即可。
解决方案
Facebook问这个问题。
一个建筑商正在寻求建造一排可能是K不同颜色的房屋。他的目标是最大程度地减少成本，同时确保没有两个相邻房屋的颜色相同。
鉴于n b的k矩阵，n排和kth列代表用kth颜色建造第n个房屋的成本，返回实现此目标的最低成本。
解决方案
Google问了这个问题。
给定两个在某个时候相交的单一链接列表，找到相交节点。列表是非周期性的。
例如，给定a = 3-> 7-> 8-> 10和b = 99-> 1-> 8-> 10，以值8返回节点。
在此示例中，假设具有相同值的节点是完全相同的节点对象。
在o（m + n）时间（m和n是列表的长度）和恒定空间中执行此操作。
解决方案
Snapchat问了这个问题。
给定一系列时间间隔（开始，结束）用于教室讲座（可能是重叠），请找到所需的最小房间数量。
例如，给定[（30，75），（0，50），（60，150）]，您应该返回2。
解决方案
微软问这个问题。
给定单词和由这些单词组成的字典和字符串（没有空格），请返回列表中的原始句子。如果有多个可能的重建，请退还其中任何一个。如果没有可能的重建，请返回null。
例如，给定一组单词“ Quick”，“ Brown”，“ The”，“ Fox”和字符串“ Thequickbrownfox”，您应该返回['the'the'the'，'''，''，'brown'，'fox' ]。
鉴于一组单词“床”，“浴”，“ bedbath”，“和”，“超越”和“ bedbathandbeyond”，返回['bed'，'bath'''，'bath''''effere offer]或['bedbath'，''''，''超越']。
解决方案
Google问了这个问题。
由代表董事会的布尔人组成的N矩阵为您提供了m。每个真正的布尔代表墙。每个虚假布尔人代表您可以行走的瓷砖。
鉴于此矩阵，启动坐标和端坐标，请返回从开始到达端坐标所需的最小步骤数。如果没有可能的路径，请返回null。您可以向上移动，向左，向下和向右移动。您不能穿过墙壁。您不能缠绕板的边缘。
例如，给定以下董事会：
[[f, f, f, f],
[t, t, f, t],
[f, f, f, f],
[f, f, f, f]]
start =（3，0）（左下）和结束=（0，0）（左上），到达末端所需的最小步数为7，因为我们需要通过（1，2）因为第二行的其他地方都有墙。
解决方案
Google问了这个问题。
在二进制树上实施锁定。只有当其所有后代或祖先都没有锁定时，才可以锁定或解锁二进制树节点。
设计具有以下方法的二进制树节点类：
IS_LOCKED，它返回节点是否锁定锁定，该节点试图锁定节点。如果无法锁定，则应返回false。否则，它应该锁定并返回true。解锁，解锁节点。如果无法解锁，则应返回false。否则，它应该解锁并返回true。您可以增强节点以添加父指针或您想要的任何其他属性。您可以假设该类在单线程程序中使用，因此不需要实际的锁或静音。每种方法应在O（H）中运行，其中H是树的高度。
解决方案
Facebook问这个问题。
实现与以下特殊字符匹配的正则表达式：
例如，给定正则表达“ ra”。字符串“ ray”，您的功能应返回true。字符串“ Raymond”上的同一正则表达式应返回false。
给定正则表达式".*at"字符串“聊天”上的同一正则表达式应返回false。
解决方案
Google问了这个问题。
给定单独链接列表和一个整数K，请从列表中删除KTH的最后一个元素。 k可以保证小于列表的长度。
列表很长，因此进行多个通行证非常昂贵。
在恒定的空间和一通道中执行此操作。
解决方案
Facebook问这个问题。
给定一连串的圆形，卷曲和正方形的打开和闭合括号，返回括号是否平衡（形成良好）。
例如，给定字符串“（[]）”，您应该返回true。
给定字符串“（[）]”或“（（（）”，您应该返回false。
解决方案
Palantir问了这个问题。
编写算法以证明文本是合理的。给定一系列单词和整数线长k，返回一个代表每条线的字符串列表，完全合理。
更具体地说，您应该在每行中拥有尽可能多的单词。每个单词之间应该至少有一个空间。必要时垫子额外的空间，以使每条线的长度恰好k。从左开始分布的额外空间（如果有）分布，则应尽可能同样地分布空间。
如果您只能将一个单词放在一条线上，则应在右侧用空格垫板。
每个单词都保证不会长于k。
例如，给定单词列表[“ the”，“ quick”，“ brown”，“ fox”，“跳”，“ off”，“ the”，“ lazy”，“ dog”]和k = 16，您应该返回以下内容：
[“快速棕色”，左侧“福克斯跳过”，＃2额外的空间均匀分布的“懒狗”]＃4额外的空间均匀分布
解决方案
由于亚马逊的版权侵权，问题和解决方案被取消
为您提供了一系列非阴性整数，该整数代表二维高程图，其中每个元素都是单位宽度壁，整数为高度。假设它会下雨，并且两堵墙之间的所有斑点都被填满了。
计算在O（n）时间和O（1）空间中，地图上仍有多少单位的水。
例如，给定输入[2、1、2]，我们可以在中间容纳1个单位的水。
鉴于输入[3、0、1、3、0、5]，我们可以在第一个索引中持有3个单元，第二个索引中的2个单元，第四个索引中的3个单位（我们不能保持5个单位左），因此我们可以捕获8个水。
解决方案
Google问了这个问题。
两个字符串之间的编辑距离是指将一个字符串更改为另一个字符串所需的字符插入，删除和替换的最小数量。例如，“小猫”和“坐着”之间的编辑距离是三个：代替“ k”代替“ s”，将“ e”代替为“ i”，然后添加a“ g”。
给定两个字符串，计算它们之间的编辑距离。
解决方案
简街问这个问题。
假设给您一个货币汇率表，表示为2D数组。确定是否有可能的套利：也就是说，是否有一系列交易序列，从任何货币的数量开始，因此您最终可以得到一定数量的数量，大于该货币的a。
没有交易成本，您可以交易分数。
解决方案
微软问这个问题。
计算数字序列的运行中值。也就是说，给定数字流，在每个新元素上都打印出列表的中值。
回想一下，偶数列表的中位数是两个中间数的平均值。
例如，给定序列[2、1、5、7、2、0、5]，您的算法应打印出来：
2
1.5
2
3.5
2
2
2
解决方案
Quora问这个问题。
给定一个字符串，找到可以通过在单词中任何地方插入最少数量的字符来制作的palindrome。如果可以制作最小长度的一个以上的腔，请返回词典最早的词汇（第一个字母顺序）。
例如，给定字符串“种族”，您应该返回“ ecarace”，因为我们可以向其添加三个字母（这是制作palindrome的最小数量）。还可以通过添加三个字母来从“种族”中做出其他七个回文，但“ ecarace”首先是按字母顺序排列的。
作为另一个示例，给定字符串“ Google”，您应该返回“ Elgoogle”。
解决方案
Google问了这个问题。
考虑到一系列严格地将字符“ r”，“ g”和“ b”隔离，将数组的值隔离，以便所有RS首先出现，GS排在第二，BS排在最后。您只能交换数组的元素。
在线性时间和就地进行此操作。
例如，给定数组['g'，'b'，'r'，'r'，'b'，'r'，'g']，它应该变成['r'，'r'，'r '，'g'，'g'，'b'，'b']。
解决方案
Dropbox问了这个问题。
鉴于二进制搜索树的根，找到树中的第二大节点。
解决方案
Google问了这个问题。
集合的功率集是其所有子集的集合。编写一个给定集合的函数生成其功率集。
例如，给定集合{1、2、3}，它应该返回{{}，{1}，{2}，{3}，{1，2}，{1，2}，{1，3}，{2，3} ，{1，2，3}}。
您也可以使用列表或数组来表示集合。
解决方案
微软问这个问题。
您有n张董事会。写下一个函数，给定n返回板的可能安排数量，其中n queens可以放在板上而不会互相威胁，即没有两个皇后共享相同的行，列或对角线。
解决方案
Dropbox问了这个问题。
康威（Conway）的生活游戏发生在无限的二维方形细胞板上。每个单元物都死了或活着，在每个刻度上，适用以下规则：
任何少于两个现场邻居的活细胞死亡。任何有两个或三个活的邻居的活细胞仍然活着。任何具有三个以上邻居的活细胞死亡。任何具有三个活着的邻居的死细胞都将成为现场单元。如果细胞在水平，垂直或对角线相邻，则邻居另一个细胞。
实施康威的生活游戏。它应该可以通过实时单元坐标的起始列表及其应运行的步骤数量初始化。初始化后，它应在每个步骤中打印出董事会状态。由于它是一个无限的板，因此仅打印出相关的坐标，即从最左端的活细胞到最下最下的活细胞。
您可以代表带有星号*的活细胞和带有点的死牢房. 。
解决方案
Google问了这个问题。
给定一个整数的数组，每个整数发生三次，除了一个仅发生一次整数，然后查找并返回非删除的整数。
例如，给定[6, 1, 3, 3, 3, 6, 6] ，返回1 。给定[13, 19, 13, 13] ，返回19 。
这样做
解决方案
Facebook问这个问题。
鉴于某人乘飞机的无序列表，每个航班都代表（原点，目的地）和一个起步机场，计算该人的行程。如果没有这样的行程，请返回null。如果有多个可能的行程，请返回词典最小的行程。所有航班必须在行程中使用。
例如，给定航班列表[（'sfo'，'hko'），（'yyz'，'sfo'），（'yul'，'yyz'），（'hko'，'ord'，'ord'）和启动机场“ Yul”，您应该返回列表['YUL'，'YYZ'，'sfo'，'hko'，'ord']。
给定航班列表[（'sfo'，'com'），（'com'，'yyz'）和启动机场'com'，您应该返回null。
给定航班列表[（'a'，'b'），（'a'，'c'），（'b'，'c'），（'c'，'a'）]，启动机场' a'，您应该返回列表['a'，'b'，'c'，'a'，'c']，即使['a'，'c'，'a'，'a'，'b'，'c ']也是有效的行程。但是，第一个在词典上较小。
解决方案
Google问了这个问题。
给定整数s和a目标编号k的列表，写下一个函数，该函数返回s的子集，该子集总计为k。如果无法制作这样的子集，请返回null。
整数可以在列表中出现不止一次。您可以假设列表中的所有数字都是正面的。
例如，给定S = [12, 1, 61, 5, 9, 2]和k = 24 ，返回[12、9、2、1]，因为它总和24。
解决方案
由于亚马逊的版权侵权，问题和解决方案被取消
Google问了这个问题。
我们可以通过计算其具有的反转数来确定数组A IS的“失败”。如果a [i]> a [j]，i <j。也就是说，较小的元素在较大的元素之后出现。
给定数组，计算其具有的反转数。比O（n^2）时间快。
您可以假设数组中的每个元素都是不同的。
例如，排序列表的反转为零。阵列[2，4，1，3，5]具有三个反转：（2，1），（4，1）和（4，3）。阵列[5，4，3，2，1]具有十个反转：每个不同的对形成反转。
解决方案
两个西格玛问这个问题。
使用函数rand5（），该函数将整数从1到5（包含）均匀概率返回，以实现一个函数rand7（），该功能将整数从1返回1到7（包含）。
解决方案
由于亚马逊的版权侵权，问题和解决方案被取消
Facebook问这个问题。
鉴于一系列代表公司股票价格按时间顺序排列的数字，写出了一个功能，该功能可以计算出您一次购买和出售该股票的最大利润。您必须购买才能出售。
例如，给定[9、11、8、5、7、10]，您应该返回5，因为您可以以5美元购买股票并以10美元的价格出售。
解决方案
Google问了这个问题。
给定二进制树的预订和按顺序遍历，写一个功能以重建树。
例如，给定以下预订遍历：
[a, b, d, e, c, f, g]
以及以下阶段遍历：
[d, b, e, a, f, c, g]
您应该返回以下树：
a
/
b c
/ /
d e f g
解决方案
由于亚马逊的版权侵权，问题和解决方案被取消
微软问这个问题。
假设将算术表达为二进制树。每个叶子都是整数，每个内部节点都是'+'，' - '，'∗'或'/'之一。
鉴于该树的根，请编写一个函数来评估它。
例如，给定以下树：
*
/
+ +
/ /
3 2 4 5
您应该返回45，因为它是（3 + 2） *（4 + 5）。
解决方案
Facebook问这个问题。
给定一个函数在1和k之间生成完美的随机数（包含在内），其中k是一个输入，写入一个函数，该函数将仅使用交换的数组表示为数组。
它应该在o（n）时间内运行。
提示：确保52个中的每一个！甲板的排列同样可能。
解决方案
Google问了这个问题。
实现LRU（最近使用的最少使用）缓存。它应该能够使用缓存尺寸n初始化，并包含以下方法：
设置（键，值）：将密钥设置为值。如果缓存中已经有n个项目，并且我们正在添加一个新项目，那么它还应该删除最近使用的项目。获取（键）：以键获取值。如果没有这样的关键，请返回null。每个操作都应在O（1）时间内进行。
解决方案
这个问题是苹果问的。
使用两个堆栈实现队列。回想一下，队列是具有以下方法的FIFO（首先，首次输出）数据结构：将元素插入队列中，而Dequeue则将其插入。
解决方案
Dropbox问了这个问题。
Sudoku是一个难题，您可以为您提供带有数字的9乘9个网格的部分填充。目的是用每行，列和框（3乘3个子格里德）的约束填充网格，必须包含1到9的所有数字。
实施有效的Sudoku求解器。
解决方案
微软问这个问题。
用以下方法实现URL缩短器：
提示：如果我们两次输入相同的URL怎么办？
解决方案
Google问了这个问题。
给定一个无方向的图表示为邻接矩阵和整数k，写一个函数来确定图中的每个顶点是否可以颜色，以使得没有两个相邻的顶点在大多数k颜色下使用相同的颜色共享相同的颜色。
解决方案
由于亚马逊的版权侵权，问题和解决方案被取消
由于亚马逊的版权侵权，问题和解决方案被取消
Google问了这个问题。
通过低带宽网络为两台计算机实现文件同步算法。如果我们知道两台计算机中的文件大多是相同的怎么办？
解决方案
Facebook问这个问题。
给定多个整数，请返回是否可以将其划分为两个总和相同的子集。
例如，给定多式{15、5、5、20、10、35、15、10}，它将返回true，因为我们可以将其拆分为{15、5、5、10、15、10}和{20、35 }，两者总计为55。
给定多式{15、5、20、10、35}，它将返回false，因为我们不能将其分为两个子集，总和相同。
解决方案
Google问了这个问题。
实施整数指控。也就是说，实现POW（x，y）函数，其中x和y是整数并返回x^y。
比重复乘法的幼稚方法更快。
例如，POW（2，10）应返回1024。
解决方案
Facebook问这个问题。
有一个n乘以零矩阵。给定n和m，写一个函数来计算从左上角开始并延伸到右下角的方式的数量。您只能向右移动或向下移动。
例如，给定2乘2矩阵，您应该返回2，因为有两种方法可以到达底部：
给定5乘5矩阵，有70种方法可以到达底线。
解决方案
微软问这个问题。
给定字符和目标词的2D矩阵，写下一个函数，该函数返回是否可以通过从左到右或最新来在矩阵中找到单词。
例如，给定以下矩阵：
[['F', 'A', 'C', 'I'],
['O', 'B', 'Q', 'P'],
['A', 'N', 'O', 'B'],
['M', 'A', 'S', 'S']]
和目标词“泡沫”，您应该返回true，因为它是最左边的列。同样，给定目标单词“质量”，您应该返回true，因为这是最后一行。
解决方案
Google问了这个问题。
骑士的巡回演出是骑士在棋盘上的一系列动作，使所有正方形都曾经参观过。
给定n，写一个功能，以返回n棋盘上N骑士旅行的数量。
解决方案
由于亚马逊的版权侵权，问题和解决方案被取消
Square问了这个问题。
假设您可以访问一个函数toss_biased（），该函数返回0或1的概率不是50-50（但也不是0-100或100-0）。您不知道硬币的偏见。
编写一个函数来模拟无偏的硬币折腾。
解决方案
Google问了这个问题。
实现LFU（最少使用的）缓存。它应该能够使用缓存尺寸n初始化，并包含以下方法：
set(key, value) ：将密钥设置为值。如果缓存中已经有n个项目，并且我们正在添加一个新项目，那么它也应删除最不常用的项目。如果有领带，则应删除最近使用的密钥。get(key) ：以键获取值。如果没有这样的关键，请返回null。每个操作都应在O（1）时间内进行。
解决方案
Google问了这个问题。
在我们的特殊棋盘上，如果两个主教共享相同的对角线，则两个主教互相攻击。这包括主教，在他们之间有另一个主教，即主教可以通过碎片攻击。
给您n个主教，由M棋盘在M上表示为（行，列）。编写一个函数来计算相互攻击的主教对数。两对的顺序并不重要：（1，2）被认为与（2，1）相同。
例如，给定M = 5和主教名单：
(0, 0)
(1, 2)
(2, 2)
(4, 0)
董事会看起来像这样：
[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]
您应该返回2，因为主教1和3相互攻击，以及主教3和4。
解决方案
Facebook问这个问题。
给定整数列表，请返回可以通过乘以任何三个整数来制造的最大产品。
例如，如果列表为[-10，-10、5、2]，我们应该返回500，因为那是-10 _ -10 _ 5。
您可以假设列表至少具有三个整数。
解决方案
如果其数字总计达到10个，则将数字视为完美。
鉴于正整数n，请返回第n个完美数字。
例如，给定1个，您应该返回19。给定2，您应该返回28。
解决方案
两个西格玛问这个问题。
使用函数rand7（），该函数将整数从1到7（包含）均匀概率返回，以实现一个函数rand5（），该函数rand5（）返回1到5（包含）。
（重复问题 - 问题45）
解决方案
Google问了这个问题。
在有向图中，为每个节点分配一个大写字母。我们将路径的值定义为沿该路径最常见的字母的数量。例如，如果图中的路径通过“ abaca”，则该路径的值为3，因为路径上有3种出现'a'。
给定带有n个节点和M导向边缘的图形，返回图形的最大值路径。如果最大的值是无限的，则返回null。
该图用字符串和边缘列表表示。第i-th角色代表第i-th节点的大写字母。边缘列表中的每个元组（i，j）意味着从第i-th节点到j-th节点都有一个定向边缘。自我编号是可能的，也是多边缘的。
例如，以下输入图：
ABACA
[(0, 1),
(0, 2),
(2, 3),
(3, 4)]
使用顶点的路径[0, 2, 3, 4], (A, A, C, A)具有最大值3。
以下输入图：
A
[(0, 0)]
应该返回null，因为我们有一个无限的循环。
解决方案
Google问了这个问题。
鉴于单独链接列表的头部，将其定为就位。
解决方案
这个问题是苹果问的。
假设您有一个由n的乘法表。也就是说，一个2D数组，其中第i-th行和j-th列的值为（i + 1）_（j + 1）（如果0-索引）或i _ j（如果1个索引）。
给定的整数n和x，写一个函数，该函数返回x在n乘以n乘法表中以n为n的值。
例如，给定n = 6和x = 12，您应该返回4，因为乘法表看起来像这样：
| 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 |
桌上有4个12。
解决方案
微软问这个问题。
给定数字数组，找到阵列中最长增加子序列的长度。子序列不一定必须是连续的。
例如，给定阵列[0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15] ，最长增加的子序列的长度为6：它是0, 2, 6, 9, 11, 15 。
解决方案
Google问了这个问题。
您将通过小写字母的M 2D矩阵给您n。确定可以删除的最小列数，以确保每行从上到下词典上排序。也就是说，每行沿着每一行时，每一列的字母在词典上是词典。是否在词典上订购了每一行本身是否无关紧要。
例如，下表：
cba
daf
ghi
由于中心中的A，这不是订购的。我们可以删除第二列以使其排序：
ca
df
gi
因此，您的功能应返回1，因为我们只需要删除1列即可。
作为另一个例子，下表：
abcdef
您的功能应返回0，因为排已经排序（只有一行）。
作为另一个例子，下表：
zyx
wvu
tsr
您的功能应返回3，因为我们需要删除所有列以订购它。
解决方案
Snapchat问了这个问题。
给定可能重叠间隔的列表，请返回一个新的间隔列表，其中已合并了所有重叠的间隔。
输入列表不一定以任何方式订购。
例如，给定[(1, 3), (5, 8), (4, 10), (20, 25)] ，您应该返回[(1, 3), (4, 10), (20, 25)] 。
解决方案
Google最近问了这个问题。
给定的K分类单链接列表，写一个函数，将所有列表合并到一个分类的单链接列表中。
解决方案
Facebook问这个问题。
给定一个整数数组，编写一个函数来确定数组是否可以通过修改最多1个元素来降低。
例如，给定数组[10, 5, 7] ，您应该返回true，因为我们可以将10个修改为1使数组不折叠。
给定数组[10, 5, 1] ，您应该返回false，因为我们无法修改任何一个元素以获取非折叠数组。
解决方案
Google问了这个问题。
鉴于二进制树的根，请返回最深的节点。例如，在以下树中，返回d。
a
/
b c
/
d
解决方案
Yelp问了这个问题。
给定数字映射到字母（如电话号码）和数字字符串，返回数字可以代表的所有可能的字母。您可以假设映射中的每个有效数字是一个数字。
For example if {'2': ['a', 'b', 'c'], '3': ['d', 'e', 'f'], } then "23" should return ['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf'] .
解决方案
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 "".
解决方案
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
解决方案
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.
解决方案
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.
解决方案
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.例如：
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
被认为有效。
解决方案
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.
解决方案
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。
解决方案
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).
解决方案
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 ())解决方案
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'] .
解决方案
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.
解决方案
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.
解决方案
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)?
解决方案
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]] .
解决方案
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.
考虑以下示例：
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
解决方案
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.
解决方案
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.
解决方案
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).
解决方案
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.
例子：
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 .解决方案
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].
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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
解决方案
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.
解决方案
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?
解决方案
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]] .
解决方案
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.
解决方案
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). “
解决方案
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?
解决方案
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"
解决方案
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.
解决方案
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.
解决方案
This problem was asked by Facebook.
Given a binary tree, return the level of the tree with minimum sum.
解决方案
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] .
解决方案
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} .
解决方案
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.
解决方案
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'.
解决方案
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.
解决方案
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:
解决方案
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
解决方案
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.
解决方案
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?
解决方案
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
解决方案
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:
解决方案
Given a real number n, find the square root of n. For example, given n = 9, return 3.
解决方案
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 .
解决方案
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.
解决方案
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?
解决方案
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.解决方案
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
解决方案
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.
解决方案
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¢.
解决方案
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
解决方案
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?
解决方案
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
解决方案
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.
解决方案
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?
解决方案
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 .
解决方案
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.
解决方案
Given a list, sort it using this method: reverse(lst, i, j) , which sorts lst from i to j .
解决方案
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] .
解决方案
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.
解决方案
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)] .
解决方案
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
变成
B B G
G G G
G G G
B B B
解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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 .
解决方案
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 .
解决方案
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 .
解决方案
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.
解决方案
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 .
解决方案
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:
解决方案
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.
解决方案
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.
解决方案
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解决方案
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.
解决方案
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)] .
解决方案
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?
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
This problem was asked by Microsoft.
Describe and give an example of each of the following types of polymorphism:
解决方案
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 } .
解决方案
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.
解决方案
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 .
解决方案
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?甚至重要吗？ Write a program to simulate the two games and calculate their expected value.
解决方案
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
解决方案
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.
解决方案
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"] .
解决方案
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.
解决方案
This problem was asked by Twitch.
Describe what happens when you type a URL into your browser and press Enter.
解决方案
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
}
和
{
"top_left": (0, 5),
"dimensions" (4, 3) # width, height
}
return 6 .
解决方案
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.
解决方案
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.
解决方案
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?
解决方案
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] .
解决方案
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 .
解决方案
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.
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
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] .
解决方案
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.
解决方案
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] .
解决方案
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 "()()()()" .
解决方案
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] .
解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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 .
解决方案
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"] .
解决方案
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.
解决方案
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 .
解决方案
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".
解决方案
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?
解决方案
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] .
解决方案
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".
解决方案
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'] .
解决方案
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 .
解决方案
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.
解决方案
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 .
解决方案
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.
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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/ .
解决方案
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.
解决方案
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 .
解决方案
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'] .
解决方案
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.
解决方案
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 .
解决方案
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}
解决方案
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 .
解决方案
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.
解决方案
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
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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).
解决方案
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).
解决方案
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 .
解决方案
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?
解决方案
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.
解决方案
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.解决方案
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] 。
解决方案
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),等等。 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).
解决方案
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 .
解决方案
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 .
解决方案
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.
解决方案
This problem was asked by Nvidia.
Find the maximum of two numbers without using any if-else statements, branching, or direct comparisons.
解决方案
This problem was asked by Salesforce.
Given an array of integers, find the maximum XOR of any two elements.
解决方案
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.
解决方案
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.
解决方案
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
解决方案
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
解决方案
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.
解决方案
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 .
解决方案
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) .
解决方案
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] .
解决方案
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.
解决方案
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] .
解决方案
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.
解决方案
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 (.,?,!,‽) .解决方案
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.
解决方案
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] .
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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 .
解决方案
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 .
解决方案
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.
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
This problem was asked by Pandora.
Given an undirected graph, determine if it contains a cycle.
解决方案
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.
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
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?
解决方案
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)] .
解决方案
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')] .
解决方案
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.该过程如下：
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 .
解决方案
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:
| 一个 | 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.
解决方案
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'] |
解决方案
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.
解决方案
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]
}
解决方案
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] .
解决方案
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 .
解决方案
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?
解决方案
This problem was asked by Etsy.
Given a sorted array, convert it into a height-balanced binary search tree.
解决方案
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.
解决方案
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' : {}
}解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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?
解决方案
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?
解决方案
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.
解决方案
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.
解决方案
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) .
解决方案
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.
解决方案
This problem was asked by Pivotal.
Write an algorithm that finds the total number of set bits in all integers between 1 and N .
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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.
这是一个示例：
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.
解决方案
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 .
解决方案
This problem was asked by Yahoo.
Write a function that returns the bitwise AND of all integers between M and N , inclusive.
解决方案
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.
解决方案
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]] .
解决方案
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 .
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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 .
解决方案
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
解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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
解决方案
This problem was asked by Apple.
Given a linked list, uniformly shuffle the nodes. What if we want to prioritize space over time?
解决方案
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 ).
解决方案
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 .
解决方案
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)] .
解决方案
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.
解决方案
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.
解决方案
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) .
解决方案
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.
解决方案
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) ?
解决方案
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.
解决方案
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 .
解决方案
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.
解决方案
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.
解决方案
This problem was asked by Uber.
Write a program that determines the smallest number of perfect squares that sum up to N .
这里有几个例子：
N = 4 , return 1 (4)N = 17 , return 2 (16 + 1)N = 18 , return 2 (9 + 9)解决方案
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.
解决方案
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.
解决方案
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.
解决方案
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:
解决方案
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 .
解决方案
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.
解决方案
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.
这里有几个例子：
(00)((00)(00))((((00)0)0)0)Given this representation, determine the depth of the tree.
解决方案
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.解决方案
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 .
解决方案
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] .
解决方案
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}
解决方案
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.
解决方案
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
解决方案
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.
解决方案
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) .
解决方案
