【python】Leetcode(primer)

本文精选LeetCode上经典算法题目,涵盖数组、字符串、动态规划、数据结构等核心主题,提供详细的解题思路与代码实现。

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(2019.7.26)不断更新中……



1217. 玩筹码

数轴上放置了一些筹码,每个筹码的位置存在数组 chips 当中。

你可以对 任何筹码 执行下面两种操作之一(不限操作次数,0 次也可以):

将第 i 个筹码向左或者右移动 2 个单位,代价为 0。
将第 i 个筹码向左或者右移动 1 个单位,代价为 1。
最开始的时候,同一位置上也可能放着两个或者更多的筹码。

返回将所有筹码移动到同一位置(任意位置)上所需要的最小代价。

示例 1:

输入:chips = [1,2,3]
输出:1
解释:第二个筹码移动到位置三的代价是 1,第一个筹码移动到位置三的代价是 0,总代价为 1。
示例 2:

输入:chips = [2,2,2,3,3]
输出:2
解释:第四和第五个筹码移动到位置二的代价都是 1,所以最小总代价为 2。

提示:

1 <= chips.length <= 100
1 <= chips[i] <= 10^9


一开始想着是往众数还是平均数来着,结果……

移动 1 下,代价 1,也即奇变偶,偶变奇代价为 1
移动 2 下,代价 0,奇偶不变代价为 0

所有数往一个位置移动,说白了,所有数字通过 ± 1 ± 2 变成一样

最终一样的数不是奇数就是偶数,

假如最终的数为奇数,则原始数组中,所有奇数变成该数字时代价为 0,每个偶数变成该数字时代价为 1,此时统计原数组中偶数的个数即可

假如最终的数为偶数,则原始数组中,所有偶数变成该数字时代价为 0,每个奇数变成该数字时代价为 1,此时统计原数组中奇数的个数即可

综合上述两种情况,最小代价就是原数组中奇数数量和偶数数量中较小的那个

class Solution(object):
    def minCostToMoveChips(self, position):
        """
        :type position: List[int]
        :rtype: int
        """
        odd = 0
        even = 0
        
        for i in position:
            if i % 2 == 0:
                even += 1
            else:
                odd += 1
        return min(odd,even)

977. 有序数组的平方

给定一个按非递减顺序排序的整数数组 A,返回每个数字的平方组成的新数组,要求也按非递减顺序排序。

  • 示例 1:
    输入:[-4,-1,0,3,10]
    输出:[0,1,9,16,100]

  • 示例 2:
    输入:[-7,-3,2,3,11]
    输出:[4,9,9,49,121]

  • 提示:
    1 <= A.length <= 10000
    -10000 <= A[i] <= 10000
    A 已按非递减顺序排序。

先忽略掉顺序,用最暴力的方法,遍历,平方, 排序

class Solution(object):
    def sortedSquares(self, A):
        """
        :type A: List[int]
        :rtype: List[int]
        """
        return sorted([i**2 for i in A])

还有可以用归并排序,两个指针(bryant)

728. 自除数

自除数 是指可以被它包含的每一位数除尽的数。

例如,128 是一个自除数,因为 128 % 1 == 0,128 % 2 == 0,128 % 8 == 0。

还有,自除数不允许包含 0 。

给定上边界和下边界数字,输出一个列表,列表的元素是边界(含边界)内所有的自除数。

  • 示例 1:
    输入:
    上边界left = 1, 下边界right = 22
    输出: [1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 15, 22]
    注意:

每个输入参数的边界满足 1 <= left <= right <= 10000。

class Solution(object):
    def selfDividingNumbers(self, left, right):
        """
        :type left: int
        :type right: int
        :rtype: List[int]
        """
        list1 = []
        for num in range(left,right+1): # 遍历区间的每一个数字
            sum1 = 0 # 记录是否每个数都除的尽

            if '0' in str(num): # 跳过包含 0 的项
                continue

            for item in str(num): # 遍历每一个数字的每一位
                if num % int(item) == 0: #自除数
                    sum1+=1

            if sum1 == len(str(num)): #if 每个数都除的尽
                list1.append(num)
        return list1

507. 完美数

对于一个 正整数,如果它和除了它自身以外的所有正因子之和相等,我们称它为“完美数”。

给定一个 整数 n, 如果他是完美数,返回 True,否则返回 False

  • 示例:
    输入: 28
    输出: True
    解释: 28 = 1 + 2 + 4 + 7 + 14

  • 提示:
    输入的数字 n 不会超过 100,000,000. (1e8)

思路:要注意,1不符合条件,不过貌似测试样例会给负数,因为负数的小数次幂得到的是复数,一直报错!我们只用遍历 2到 sqrt(num) 即可

class Solution(object):
    def checkPerfectNumber(self, num):
        """
        :type num: int
        :rtype: bool
        """
        if num <= 1: # 这个限制很关键
            return False
        sum1 = 1
        for i in range(2,int(num**0.5)+1):
            if num % i == 0:
                sum1+= i
                sum1+=num//i

        if num == sum1:
            return True
        else:
            return False

908. 最小差值 I

给定一个整数数组 A,对于每个整数 A[i],我们可以选择任意 x 满足 -K <= x <= K,并将 x 加到 A[i] 中。

在此过程之后,我们得到一些数组 B。

返回 B 的最大值和 B 的最小值之间可能存在的最小差值。

  • 示例 1:
    输入:A = [1], K = 0
    输出:0
    解释:B = [1]

  • 示例 2:
    输入:A = [0,10], K = 2
    输出:6
    解释:B = [2,8]

  • 示例 3:
    输入:A = [1,3,6], K = 3
    输出:0
    解释:B = [3,3,3] 或 B = [4,4,4]

  • 提示:
    1 <= A.length <= 10000
    0 <= A[i] <= 10000
    0 <= K <= 10000

思路:相当于 A 中的每个数字在 [-K,K] 的范围内波动,求波动后 B 中最大元素与最小元素差值的最小值!我们先计算出原来 A 中的差值,然后比较差值与 2K 的大小,如果小于 2K,那么最小差值能被波动抹平,自然是0,如果大于 2K,波动最多只能缩小 2K 的差距,也即 max - K and min+K

class Solution(object):
    def smallestRangeI(self, A, K):
        """
        :type A: List[int]
        :type K: int
        :rtype: int
        """
        A_min = min(A)
        A_max = max(A)
        
        result = A_max - A_min - 2*K
        
        if result > 0:
            return result
        else:
            return 0

剑指 Offer 64. 求1+2+…+n (and)

https://leetcode-cn.com/problems/qiu-12n-lcof

求 1+2+…+n ,要求不能使用乘除法、for、while、if、else、switch、case等关键字及条件判断语句(A?B:C)。

示例 1:

输入: n = 3
输出: 6


难点在于限制条件,我们用 and 关键字 (短路效应及其特性) 来代替 if,用递归调用来代替使用 for 或者 while

逻辑运算符的短路效应:

常见的逻辑运算符有三种,即 “与 && ”,“或 || ”,“非 !” ;而其有重要的短路效应,如下所示:
if(A && B) // 若 A 为 false ,则 B 的判断不会执行(即短路),直接判定 A && B 为 false
if(A || B) // 若 A 为 true ,则 B 的判断不会执行(即短路),直接判定 A || B 为 true

作者:jyd
链接:https://leetcode-cn.com/problems/qiu-12n-lcof/solution/mian-shi-ti-64-qiu-1-2-nluo-ji-fu-duan-lu-qing-xi-/
来源:力扣(LeetCode)

and 只要左边的表达式为真,整个表达式返回的值是右边表达式的值,否则,返回左边表达式的值

class Solution(object):
    def sumNums(self, n):
        """
        :type n: int
        :rtype: int
        """
        # return n*(n+1)/2
        return n and self.sumNums(n-1) + n

以 n = 3 为例

return 3 and f(2)+3
return 2 and f(1)+2
return 1 and f(0)+1
return 0 and f(-1)+0

递归
return 0 and f(-1)+0 => return 0
return 1 and f(0)+1 => return 1 and 0+1 => return 1 and 1 => return 1
return 2 and f(1)+2 => return 2 and 1+2 => return 2 and 3 => return 3
return 3 and f(2)+3 => return 3 and 3+3 => return 3 and 6 => return 6

答案为 6


462. 最少移动次数使数组元素相等 II(中位数)

给定一个非空整数数组,找到使所有数组元素相等所需的最小移动数,其中每次移动可将选定的一个元素加1或减1。 您可以假设数组的长度最多为10000。

  • 例如:
    输入:
    [1,2,3]
    输出:
    2

  • 说明:
    只有两个动作是必要的(记得每一步仅可使其中一个元素加1或减1):
    [1,2,3] => [2,2,3] => [2,2,2]

思路,排序后找到中位数,到中位数的移动次数最少(其实我也没有能完全 get,为什么到中位数移动次数最少,最好是能证明一下,哈哈哈)!

class Solution(object):
    def minMoves2(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        nums = sorted(nums)
        
        l = len(nums)

        if l % 2 == 0:
            mid = (nums[l/2] + nums[(l-1)/2]) // 2
        else:
            mid = nums[l//2]

        sum1 = 0

        for i in nums:
            sum1+= abs(mid-i)
            
        return sum1

还有解题思路是相遇!(bryant)

1. 两数之和(无序用Hash)

给定一个整数数组 nums 和一个目标值 target,请你在该数组中找出和为目标值的那两个整数,并返回他们的数组下标。
你可以假设每种输入只会对应一个答案。但是,你不能重复利用这个数组中同样的元素。

  • 示例:
    给定 nums = [2, 7, 11, 15], target = 9
    因为 nums[0] + nums[1] = 2 + 7 = 9
    所以返回 [0, 1]

1)暴力法
两层循环嘛

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        for i in range(len(nums)-1):# 0-倒数第二个
            for j in range(i+1,len(nums)): # i的下一个到最后一个
                if nums[i]+ nums[j] == target:
                    return [i,j]

2)Hash 表
思路
建立一个字典,keys 存当前元素达到 target 所需要的数值,values 存的是当前元素的下标!(也就是说第 values 个元素需要找 keys 才能匹配成功!)
遍历数组元素,判断元素是否在字典的 keys 中
如果在,匹配成功,返回元素下标和字典的 values(也即自己另一半在数组中的下标)!
如果不在,新增一个字典 item,将该元素达到 target 所需的数字存为 keys,该元素下标存为 values!参考 [LeetCode]1.TwoSum(Python实现)

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        dict1 = {}
        for i,num in enumerate(nums):
            if  nums[i] in dict1:
                return [i,dict1[nums[i]]] 
            else:
                dict1[target-nums[i]] = i

167. 两数之和 II - 输入有序数组(双指针) 有序的话用双指针就可以

75. 颜色分类(荷兰国旗)

给定一个包含红色、白色和蓝色,一共 n 个元素的数组,原地对它们进行排序,使得相同颜色的元素相邻,并按照红色、白色、蓝色顺序排列。

此题中,我们使用整数 0、 1 和 2 分别表示红色、白色和蓝色。

  • 注意:
    不能使用代码库中的排序函数来解决这道题。

  • 示例:
    输入: [2,0,2,1,1,0]
    输出: [0,0,1,1,2,2]

  • 进阶:
    一个直观的解决方案是使用计数排序的两趟扫描算法。
    首先,迭代计算出0、1 和 2 元素的个数,然后按照0、1、2的排序,重写当前数组。
    你能想出一个仅使用常数空间的一趟扫描算法吗?


1)桶排序

第一个想法当然是桶排序,参考本博客 347. 前 K 个高频元素 中对桶排序的描述!

class Solution(object):
    def sortColors(self, nums):
        """
        :type nums: List[int]
        :rtype: None Do not return anything, modify nums in-place instead.
        """
        buckets = [0]*3

        for i in nums:
            buckets[i]+=1
            
        del nums[:] # 哈哈很精髓,注释中说了不要改
        
        for i in range(len(buckets)):
            if buckets[i]:
                nums.extend([i]* buckets[i])

不过题目要求原地算法,所以有瑕疵!

在计算机科学中,一个原地算法(in-place algorithm)是一种使用小的,固定数量的额外之空间来转换资料的算法。当算法执行时,输入的资料通常会被要输出的部份覆盖掉。不是原地算法有时候称为非原地(not-in-place)或不得其所(out-of-place)——百度百科

2)利用快排序的思想

这个问题我们可以将这个问题视为一个数组排序问题,这个数组分为前部,中部和后部(0,1,2)三个部分!

思路如下:将前部和后部各排在数组的前边和后边,中部自然就排好了。具体的:

设置两个标志位 begin 和 end 分别指向这个数组的开始和末尾,然后用一个标志位 current 从头开始进行遍历:

  • 若遍历到的位置为 0,则说明它一定属于前部,于是就和 begin 位置进行交换,然后 current 向前进,begin 也向前进(表示前边的已经都排好了)。
  • 若遍历到的位置为 1,则说明它一定属于中部,根据总思路,中部的我们都不动,然后 current 向前进。
  • 若遍历到的位置为 2,则说明它一定属于后部,于是就和 end 位置进行交换,由于交换完毕后 current 指向的可能是属于前部的,若此时 current 前进则会导致该位置不能被交换到前部,所以此时 current 不前进),end 向后退1。

参考

class Solution(object):
    def sortColors(self, nums):
        """
        :type nums: List[int]
        :rtype: None Do not return anything, modify nums in-place instead.
        """
        start = 0
        end = len(nums)-1
        current = 0

        while current<=end:
            if nums[current]==2: # 这里没有 current++ 小心这个坑
                nums[current],nums[end] = nums[end], nums[current]
                end-=1
            elif nums[current]==0:
                nums[current],nums[start] = nums[start], nums[current]
                current+=1
                start+=1
            else:
                current+=1

999. 车的可用捕获量(上下左右遍历)

在一个 8 x 8 的棋盘上,有一个白色车(rook)。也可能有空方块,白色的象(bishop)和黑色的卒(pawn)。它们分别以字符 “R”,“.”,“B” 和 “p” 给出。大写字符表示白棋,小写字符表示黑棋。

车按国际象棋中的规则移动:它选择四个基本方向中的一个(北,东,西和南),然后朝那个方向移动,直到它选择停止、到达棋盘的边缘或移动到同一方格来捕获该方格上颜色相反的卒。另外,车不能与其他友方(白色)象进入同一个方格。

返回车能够在一次移动中捕获到的卒的数量。
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思路:定位到车的位置,然后以车为原点,上下左右四条路出发,if 遇到象就直接break,else 遇到兵,结果+1,也 break(注意:因为不可能是肉弹战车,横扫千军)

class Solution(object):
    def numRookCaptures(self, board):
        """
        :type board: List[List[str]]
        :rtype: int
        """
        # 定位
        flag = False
        for row in range(len(board)):
            for col in range(len(board[0])):
                if board[row][col] == "R":
                    flag = True
                    break
            if flag == True:
                break
                
        count = 0
		# 上
        for i in reversed(range(row)):
            if board[i][col] == "B":
                break
            elif board[i][col] == "p":
                count+=1
                break
		# 下
        for i in range(row+1,len(board[0])):
            if board[i][col] == "B":
                break
            elif board[i][col] == "p":
                count+=1   
                break
		# 左
        for j in reversed(range(col)):
            if board[row][j] == "B":
                break
            elif board[row][j] == "p":
                count+=1
                break
		# 右
        for j in range(col+1,len(board)):
            if board[row][j] == "B":
                break
            elif board[row][j] == "p":
                count+=1  
                break
        return count

766. 托普利茨矩阵(比较两行)

如果一个矩阵的每一方向由左上到右下的对角线上具有相同元素,那么这个矩阵是托普利茨矩阵。

给定一个 M x N 的矩阵,当且仅当它是托普利茨矩阵时返回 True。

示例 1:

输入:
matrix = [
[1,2,3,4],
[5,1,2,3],
[9,5,1,2]
]
输出: True
解释:
在上述矩阵中, 其对角线为:
“[9]”, “[5, 5]”, “[1, 1, 1]”, “[2, 2, 2]”, “[3, 3]”, “[4]”。
各条对角线上的所有元素均相同, 因此答案是True。
示例 2:

输入:
matrix = [
[1,2],
[2,2]
]
输出: False
解释:
对角线"[1, 2]"上的元素不同。

思路:这个题一开始准备找对角线的规律,但是发现很难找,再仔细想想,每行的第一个到倒数第二个应该和下一行的第二个到最后一个相等,才能满足条件!这样的话,问题就容易了很多!

class Solution(object):
    def isToeplitzMatrix(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: bool
        """
        m = len(matrix)
        n = len(matrix[0])
        for i in range(m-1):
            if matrix[i][:-1] != matrix[i+1][1:]:
                return False
        return True

1103. 分糖果 II

排排坐,分糖果。

我们买了一些糖果 candies,打算把它们分给排好队的 n = num_people 个小朋友。

给第一个小朋友 1 颗糖果,第二个小朋友 2 颗,依此类推,直到给最后一个小朋友 n 颗糖果。

然后,我们再回到队伍的起点,给第一个小朋友 n + 1 颗糖果,第二个小朋友 n + 2 颗,依此类推,直到给最后一个小朋友 2 * n 颗糖果。

重复上述过程(每次都比上一次多给出一颗糖果,当到达队伍终点后再次从队伍起点开始),直到我们分完所有的糖果。注意,就算我们手中的剩下糖果数不够(不比前一次发出的糖果多),这些糖果也会全部发给当前的小朋友。

返回一个长度为 num_people、元素之和为 candies 的数组,以表示糖果的最终分发情况(即 ans[i] 表示第 i 个小朋友分到的糖果数)。

  • 示例 1:
    输入:candies = 7, num_people = 4
    输出:[1,2,3,1]

  • 示例 2:
    输入:candies = 10, num_people = 3
    输出:[5,2,3]

思路:位置+1,糖果数+1,位置要对总人数取余数达到循环的效果!取剩余糖果数和当前位置该发的糖果数的最小值来发糖果!

class Solution(object):
    def distributeCandies(self, candies, num_people):
        """
        :type candies: int
        :type num_people: int
        :rtype: List[int]
        """
        result = [0]*num_people
        position = 0 # 给该位置学生发糖果
        candy = 1 # 发糖果的数量

        while(candies>0): # 当剩余糖果大于0
            result[position] += min(candy,candies) # 取 应该发的,和剩有的糖果的最小值
            candies -= candy # 糖果总数减去发的糖果
            position+=1 # 下一位同学
            position = position % num_people # 取余
            candy+=1 # 该发的糖果数+1
        return result

1030. 距离顺序排列矩阵单元格

给出 R 行 C 列的矩阵,其中的单元格的整数坐标为 (r, c),满足 0 <= r < R 且 0 <= c < C。

另外,我们在该矩阵中给出了一个坐标为 (r0, c0) 的单元格。

返回矩阵中的所有单元格的坐标,并按到 (r0, c0) 的距离从最小到最大的顺序排,其中,两单元格(r1, c1) 和 (r2, c2) 之间的距离是曼哈顿距离,|r1 - r2| + |c1 - c2|。(你可以按任何满足此条件的顺序返回答案。)

  • 示例 1:
    输入:R = 1, C = 2, r0 = 0, c0 = 0
    输出:[[0,0],[0,1]]
    解释:从 (r0, c0) 到其他单元格的距离为:[0,1]

思路:遍历矩阵,用二维数组存放坐标和距离,行是距离,列是对应的坐标,因为存在一个距离对应多个坐标的情况,然后遍历二维数组,依次取出坐标

class Solution(object):
    def allCellsDistOrder(self, R, C, r0, c0):
        """
        :type R: int
        :type C: int
        :type r0: int
        :type c0: int
        :rtype: List[List[int]]
        """
        list1 = [[] for i in range(200)] # 这里创建的数组需要是二维,行值,列坐标,存在一值多坐标,所以要初始化为二维

        for i in range(R):
            for j in range(C):
                list1[abs(i-r0)+ abs(j-c0)].append([i,j])  # 根据题意来填补值和坐标

        result = []  
        for i in list1: # 遍历列表
            if i:
                result.extend(i) # 因为存在一值多坐标的情况,所以不是 append,而是 extend
        return result

283. 移动零

给定一个数组 nums,编写一个函数将所有 0 移动到数组的末尾,同时保持非零元素的相对顺序。

  • 示例:
    输入: [0,1,0,3,12]
    输出: [1,3,12,0,0]

思路:第一个非零的数移动到第一个位置,原来的位置置为0,第二个非零的数移动到第二个位置,原来的位置置为0,需要注意的是,如果没有发生移动的情况,就不应该有置零的操作,不然那个数字就消失了,我通过 count 计数来实现这个不移动的情况!

class Solution(object):
    def moveZeroes(self, nums):
        """
        :type nums: List[int]
        :rtype: None Do not return anything, modify nums in-place instead.
        """
        count = 0
        for i in range(len(nums)):
            if nums[i] != 0:
                nums[count] = nums[i]
                if i != count: # 第i(下标0)个位置,有i个非零的数,就不能置零了
                    nums[i] = 0
                count+=1 # 统计非零的次数
        return nums

1185. 一周中的第几天

给你一个日期,请你设计一个算法来判断它是对应一周中的哪一天。

输入为三个整数:day、month 和 year,分别表示日、月、年。

您返回的结果必须是这几个值中的一个 {“Sunday”, “Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday”, “Saturday”}。

  • 示例 1:
    输入:day = 31, month = 8, year = 2019
    输出:“Saturday”

思路:1年1月1日是星期一,统计离1年1月1日过了多少天,模 7,计算星期几

class Solution(object):
    def dayOfTheWeek(self, day, month, year):
        """
        :type day: int
        :type month: int
        :type year: int
        :rtype: str
        """
        # month = 3, 统计 1,2月份日期之和
        # 非闰年,365 天
        month_no = {
            1:0,
            2:31,
            3:31+28,
            4:31+28+31,
            5:31+28+31+30,
            6:31+28+31+30+31,
            7:31+28+31+30+31+30,
            8:31+28+31+30+31+30+31,
            9:31+28+31+30+31+30+31+31,
            10:31+28+31+30+31+30+31+31+30,
            11:31+28+31+30+31+30+31+31+30+31,
            12:31+28+31+30+31+30+31+31+30+31+30}

        # month = 3, 统计 1,2月份日期之和
        # 闰年,366 天
        month_leap = {
            1:0,
            2:31,
            3:31+29,
            4:31+29+31,
            5:31+29+31+30,
            6:31+29+31+30+31,
            7:31+29+31+30+31+30,
            8:31+29+31+30+31+30+31,
            9:31+29+31+30+31+30+31+31,
            10:31+29+31+30+31+30+31+31+30,
            11:31+29+31+30+31+30+31+31+30+31,
            12:31+29+31+30+31+30+31+31+30+31+30}

        everyday = {
            0:"Sunday", 
            1:"Monday", 
            2:"Tuesday", 
            3:"Wednesday", 
            4:"Thursday", 
            5:"Friday", 
            6:"Saturday"}

        total_days = 0
		# 处理年,平年365,闰年366
        for i in range(1,year):
            if (i % 4 == 0 and i % 100 != 0) or (i % 400 == 0): # 如果是闰年
                total_days += 366
            else:
                total_days += 365
		# 处理月和天,区别平闰年
        if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0): # 如果是闰年
            total_days += (month_leap[month] + day)
        else:
            total_days += (month_no[month] + day)
		# 模 7 取结果
        result = everyday[(total_days)%7]
        return result

1299. 将每个元素替换为右侧最大元素

给你一个数组 arr ,请你将每个元素用它右边最大的元素替换,如果是最后一个元素,用 -1 替换。

完成所有替换操作后,请你返回这个数组。

示例:

输入:arr = [17,18,5,4,6,1]
输出:[18,6,6,6,1,-1]

提示:

1 <= arr.length <= 10^4
1 <= arr[i] <= 10^5


暴力法

result = arr[:]
for i in range(len(arr)-1):
    result[i] = max(arr[i+1:])
result[-1] = -1
return result

逆序法

思路:逆序只用遍历一次

以 [17,18,5,4,6,1] 为例

1 位置上的最终结果为 -1

6 位置上的最终结果应该是 6 位置后一位的最终结果与 6 位置的 后一位对应值的最大值,也即 max(-1,1) = 1

4 位置上的最终结果应该是 4 位置后一位的最终结果与 4 位置的 后一位对应值的最大值,也即 max(1,6) = 6

5 位置上的最终结果应该是 5 位置后一位的最终结果与 5 位置的 后一位对应值的最大值,也即 max(6,4) = 6

18 位置上的最终结果应该是 18 位置后一位的最终结果与 18 位置的 后一位对应值的最大值,也即 max(6,5) = 6

17 位置上的最终结果应该是 17 位置后一位的最终结果与 17 位置的 后一位对应值的最大值,也即 max(6,18) = 18

n = [0]*(len(arr)-1) + [-1]

for i in range(len(arr)-2, -1, -1):
    n[i] = max(n[i+1], arr[i+1])
return n

976. 三角形的最大周长

给定由一些正数(代表长度)组成的数组 A,返回由其中三个长度组成的、面积不为零的三角形的最大周长。

如果不能形成任何面积不为零的三角形,返回 0。

示例 1:

输入:[2,1,2]
输出:5
示例 2:

输入:[1,2,1]
输出:0
示例 3:

输入:[3,2,3,4]
输出:10
示例 4:

输入:[3,6,2,3]
输出:8

暴力法肯定超时

class Solution(object):
    def largestPerimeter(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        res = 0
        A = sorted(A)
        for i in range(len(A)-2):
            for j in range(i+1,len(A)-1):
                for k in range(j+1,len(A)):
                    if A[i]+A[j]>A[k] and A[i]+A[j]+A[k]>res:
                        res = A[i]+A[j]+A[k]
        return res

一个比较好的思路是,取当前长度最长的三条边,他们能组成三角形的话,周长肯定是最大的,如果组成不了,说明,第三长的边+第二长的边<最长的边,换句话说就是,数组里剩下的边与最长的边也可能组成三角形了,也即最长的边应该抛弃掉!

从余下的数组中选出最大的三条边,周而复始……

class Solution(object):
    def largestPerimeter(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        res = 0
        A = sorted(A,reverse=True)
        
        for i in range(len(A)-2):
            if A[i+1] + A[i+2] > A[i]:
                return A[i+1] + A[i+2] + A[i]
        return 0

# [LeetCode](https://leetcode.com/problemset/algorithms/) ![Language](https://img.shields.io/badge/language-Python%20%2F%20C++%2011-orange.svg) [![License](https://img.shields.io/badge/license-MIT-blue.svg)](./LICENSE.md) ![Progress](https://img.shields.io/badge/progress-468%20%2F%20468-ff69b4.svg) Up to date (2016-12-18), there are `447` Algorithms / `13` Database / `4` Shell / `4` Draft questions on [LeetCode Online Judge](https://leetcode.com/). The number of questions is increasing recently. Here is the classification of all `468` questions. For more questions and solutions, you can see my [LintCode](https://github.com/kamyu104/LintCode) repository. I'll keep updating for full summary and better solutions. Stay tuned for updates. (Notes: "馃摉" means you need to subscribe to [LeetCode premium membership](https://leetcode.com/subscribe/) for the access to premium questions.) ## Algorithms * [Bit Manipulation](https://github.com/kamyu104/LeetCode#bit-manipulation) * [Array](https://github.com/kamyu104/LeetCode#array) * [String](https://github.com/kamyu104/LeetCode#string) * [Linked List](https://github.com/kamyu104/LeetCode#linked-list) * [Stack](https://github.com/kamyu104/LeetCode#stack) * [Queue](https://github.com/kamyu104/LeetCode#queue) * [Heap](https://github.com/kamyu104/LeetCode#heap) * [Tree](https://github.com/kamyu104/LeetCode#tree) * [Hash Table](https://github.com/kamyu104/LeetCode#hash-table) * [Data Structure](https://github.com/kamyu104/LeetCode#data-structure) * [Math](https://github.com/kamyu104/LeetCode#math) * [Two Pointers](https://github.com/kamyu104/LeetCode#two-pointers) * [Sort](https://github.com/kamyu104/LeetCode#sort) * [Recursion](https://github.com/kamyu104/LeetCode#recursion) * [Binary Search](https://github.com/kamyu104/LeetCode#binary-search) * [Binary Search Tree](https://github.com/kamyu104/LeetCode#binary-search-tree) * [Breadth-First Search](https://github.com/kamyu104/LeetCode#breadth-first-search) * [Depth-First Search](https://github.com/kamyu104/LeetCode#depth-first-search) * [Backtracking](https://github.com/kamyu104/LeetCode#backtracking) * [Dynamic Programming](https://github.com/kamyu104/LeetCode#dynamic-programming) * [Greedy](https://github.com/kamyu104/LeetCode#greedy) * [Design](https://github.com/kamyu104/LeetCode#design) ## Database * [SQL](https://github.com/kamyu104/LeetCode#sql) ## Shell * [Shell Script](https://github.com/kamyu104/LeetCode#shell-script) ## Bit Manipulation | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 136 | [Single Number](https://leetcode.com/problems/single-number/) | [C++](./C++/single-number.cpp) [Python](./Python/single-number.py) | _O(n)_ | _O(1)_ | Easy ||| 137 | [Single Number II](https://leetcode.com/problems/single-number-ii/) | [C++](./C++/single-number-ii.cpp) [Python](./Python/single-number-ii.py) | _O(n)_ | _O(1)_ | Medium ||| 190 | [Reverse Bits](https://leetcode.com/problems/reverse-bits/) | [C++](./C++/reverse-bits.cpp) [Python](./Python/reverse-bits.py) | _O(1)_ | _O(1)_ | Easy ||| 191 |[Number of 1 Bits](https://leetcode.com/problems/number-of-1-bits/) | [C++](./C++/number-of-1-bits.cpp) [Python](./Python/number-of-1-bits.py) | _O(1)_ | _O(1)_ | Easy ||| 201 | [Bitwise AND of Numbers Range](https://leetcode.com/problems/bitwise-and-of-numbers-range/) | [C++](./C++/bitwise-and-of-numbers-range.cpp) [Python](./Python/bitwise-and-of-numbers-range.py) | _O(1)_ | _O(1)_ | Medium || 231 | [Power of Two](https://leetcode.com/problems/power-of-two/) | [C++](./C++/power-of-two.cpp) [Python](./Python/power-of-two.py) | _O(1)_ | _O(1)_ | Easy | LintCode | 260 | [Single Number III](https://leetcode.com/problems/single-number-iii/) | [C++](./C++/single-number-iii.cpp) [Python](./Python/single-number-iii.py) | _O(n)_ | _O(1)_ | Medium || 268| [Missing Number](https://leetcode.com/problems/missing-number/) | [C++](./C++/missing-number.cpp) [Python](./Python/missing-number.py) | _O(n)_ | _O(1)_ | Medium | LintCode || 318| [Maximum Product of Word Lengths](https://leetcode.com/problems/maximum-product-of-word-lengths/) | [C++](./C++/maximum-product-of-word-lengths.cpp) [Python](./Python/maximum-product-of-word-lengths.py) | _O(n)_ ~ _O(n^2)_ | _O(n)_ | Medium || Bit Manipulation, Counting Sort, Pruning| 342 | [Power of Four](https://leetcode.com/problems/power-of-four/) | [C++](./C++/power-of-four.cpp) [Python](./Python/power-of-four.py) | _O(1)_ | _O(1)_ | Easy | | 371 | [Sum of Two Integers](https://leetcode.com/problems/sum-of-two-integers/) | [C++](./C++/sum-of-two-integers.cpp) [Python](./Python/sum-of-two-integers.py) | _O(1)_ | _O(1)_ | Easy | LintCode | 389 | [Find the Difference](https://leetcode.com/problems/find-the-difference/) | [C++](./C++/find-the-difference.cpp) [Python](./Python/find-the-difference.py) | _O(n)_ | _O(1)_ | Easy | | 393 | [UTF-8 Validation](https://leetcode.com/problems/utf-8-validation/) | [C++](./C++/utf-8-validation.cpp) [Python](./Python/utf-8-validation.py) | _O(n)_ | _O(1)_ | Medium | | 401 | [Binary Watch](https://leetcode.com/problems/binary-watch/) | [C++](./C++/binary-watch.cpp) [Python](./Python/binary-watch.py) | _O(1)_ | _O(1)_ | Easy | | 411 | [Minimum Unique Word Abbreviation](https://leetcode.com/problems/minimum-unique-word-abbreviation/) | [C++](./C++/minimum-unique-word-abbreviation.cpp) [Python](./Python/minimum-unique-word-abbreviation.py) | _O(2^n)_ | _O(n)_ | Hard | 馃摉 | 421 | [Maximum XOR of Two Numbers in an Array](https://leetcode.com/problems/maximum-xor-of-two-numbers-in-an-array/) | [C++](./C++/maximum-xor-of-two-numbers-in-an-array.cpp) [Python](./Python/maximum-xor-of-two-numbers-in-an-array.py) | _O(n)_ | _O(1)_ | Medium || 461 | [Hamming Distance](https://leetcode.com/problems/hamming-distance/) | [C++](./C++/hamming-distance.cpp) [Python](./Python/hamming-distance.py) | _O(1)_ | _O(1)_ | Easy || 462 | [Minimum Moves to Equal Array Elements II](https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/) | [C++](./C++/minimum-moves-to-equal-array-elements-ii.cpp) [Python](./Python/minimum-moves-to-equal-array-elements-ii.py) | _O(n)_ on average | _O(1)_ | Medium || 477 | [Total Hamming Distance](https://leetcode.com/problems/total-hamming-distance/) | [C++](./C++/total-hamming-distance.cpp) [Python](./Python/total-hamming-distance.py) | _O(n)_ | _O(1)_ | Medium || ## Array | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 15 | [3 Sum](https://leetcode.com/problems/3sum/) | [C++](./C++/3sum.cpp) [Python](./Python/3sum.py) | _O(n^2)_ | _O(1)_ | Medium || Two Pointers 16 | [3 Sum Closest](https://leetcode.com/problems/3sum-closest/) | [C++](./C++/3sum-closest.cpp) [Python](./Python/3sum-closest.py) | _O(n^2)_ | _O(1)_ | Medium || Two Pointers 18| [4 Sum](https://leetcode.com/problems/4sum/) | [C++](./C++/4sum.cpp) [Python](./Python/4sum.py) | _O(n^3)_ | _O(1)_ | Medium || Two Pointers 26 | [Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)| [C++](./C++/remove-duplicates-from-sorted-array.cpp) [Python](./Python/remove-duplicates-from-sorted-array.py) | _O(n)_ | _O(1)_ | Easy || Two Pointers 27 | [Remove Element](https://leetcode.com/problems/remove-element/) | [C++](./C++/remove-element.cpp) [Python](./Python/remove-element.py) | _O(n)_ | _O(1)_ | Easy || 31 | [Next Permutation](https://leetcode.com/problems/next-permutation/)| [C++](./C++/next-permutation.cpp) [Python](./Python/next-permutation.py) | _O(n)_ | _O(1)_ | Medium || Tricky 41 | [First Missing Positive](https://leetcode.com/problems/first-missing-positive/)| [C++](./C++/first-missing-positive.cpp) [Python](./Python/first-missing-positive.py) | _O(n)_ | _O(1)_ | Hard || Tricky 48 | [Rotate Image](https://leetcode.com/problems/rotate-image/) | [C++](./C++/rotate-image.cpp) [Python](./Python/rotate-image.py) | _O(n^2)_ | _O(1)_ | Medium || 54 | [Spiral Matrix](https://leetcode.com/problems/spiral-matrix/) | [C++](./C++/spiral-matrix.cpp) [Python](./Python/spiral-matrix.py) | _O(m * n)_ | _O(1)_ | Medium || 59 | [Spiral Matrix II](https://leetcode.com/problems/spiral-matrix-ii/) | [C++](./C++/spiral-matrix-ii.cpp) [Python](./Python/spiral-matrix-ii.py) | _O(n^2)_ | _O(1)_ | Medium || 66 | [Plus One](https://leetcode.com/problems/plus-one/) | [C++](./C++/plus-one.cpp) [Python](./Python/plus-one.py) | _O(n)_ | _O(1)_ | Easy || 73 | [Set Matrix Zeroes](https://leetcode.com/problems/set-matrix-zeroes/) | [C++](./C++/set-matrix-zeroes.cpp) [Python](./Python/set-matrix-zeroes.py) | _O(m * n)_ | _O(1)_ | Medium || 80 | [Remove Duplicates from Sorted Array II](https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/)| [C++](./C++/remove-duplicates-from-sorted-array-ii.cpp) [Python](./Python/remove-duplicates-from-sorted-array-ii.py) | _O(n)_ | _O(1)_ | Medium || Two Pointers 118 | [Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)| [C++](./C++/pascals-triangle.cpp) [Python](./Python/pascals-triangle.py) | _O(n^2)_ | _O(1)_ | Easy || 119 | [Pascal's Triangle II](https://leetcode.com/problems/pascals-triangle-ii/)| [C++](./C++/pascals-triangle-ii.cpp) [Python](./Python/pascals-triangle-ii.py) | _O(n^2)_ | _O(1)_ | Easy || 121 | [Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)| [C++](./C++/best-time-to-buy-and-sell-stock.cpp) [Python](./Python/best-time-to-buy-and-sell-stock.py) | _O(n)_ | _O(1)_ | Easy || 128 | [Longest Consecutive Sequence](https://leetcode.com/problems/longest-consecutive-sequence/)| [C++](./C++/longest-consecutive-sequence.cpp) [Python](./Python/longest-consecutive-sequence.py) | _O(n)_ | _O(n)_ | Hard || Tricky 157 | [Read N Characters Given Read4](https://leetcode.com/problems/read-n-characters-given-read4/) | [C++](./C++/read-n-characters-given-read4.cpp) [Python](./Python/read-n-characters-given-read4.py) | _O(n)_ | _O(1)_ | Easy |馃摉| 158 | [Read N Characters Given Read4 II - Call multiple times](https://leetcode.com/problems/read-n-characters-given-read4-ii-call-multiple-times/) | [C++](./C++/read-n-characters-given-read4-ii-call-multiple-times.cpp) [Python](./Python/read-n-characters-given-read4-ii-call-multiple-times.py) | _O(n)_ | _O(1)_ | Hard |馃摉| 163 | [Missing Ranges](https://leetcode.com/problems/missing-ranges/)| [C++](./C++/missing-ranges.cpp) [Python](./Python/missing-ranges.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | 169 | [Majority Element](https://leetcode.com/problems/majority-element/) | [C++](./C++/majority-element.cpp) [Python](./Python/majority-element.py) | _O(n)_ | _O(1)_ | Easy | 189 | [Rotate Array](https://leetcode.com/problems/rotate-array/) | [C++](./C++/rotate-array.cpp) [Python](./Python/rotate-array.py) | _O(n)_ | _O(1)_ | Easy || 209 | [Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/) | [C++](./C++/minimum-size-subarray-sum.cpp) [Python](./Python/minimum-size-subarray-sum.py) | _O(n)_ | _O(1)_ | Medium | | Binary Search 215 | [Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/) | [C++](./C++/kth-largest-element-in-an-array.cpp) [Python](./Python/kth-largest-element-in-an-array.py)| _O(n)_ ~ _O(n^2)_ | _O(1)_ | Medium | EPI| 228 | [Summary Ranges](https://leetcode.com/problems/summary-ranges/) | [C++](./C++/summary-ranges.cpp) [Python](./Python/summary-ranges.py)| _O(n)_ | _O(1)_ | Medium | | 229 | [Majority Element II](https://leetcode.com/problems/majority-element-ii/) | [C++](./C++/majority-element-ii.cpp) [Python](./Python/majority-element-ii.py) | _O(n)_ | _O(1)_ | Medium | | 238 | [Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/) | [C++](./C++/product-of-array-except-self.cpp) [Python](./Python/product-of-array-except-self.py) | _O(n)_ | _O(1)_ | Medium | LintCode | 240 | [Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | [C++](./C++/search-a-2d-matrix-ii.cpp) [Python](./Python/search-a-2d-matrix-ii.py) | _O(m + n)_ | _O(1)_ | Medium | EPI, LintCode | 243| [Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/) | [C++](./C++/shortest-word-distance.cpp) [Python](./Python/shortest-word-distance.py) | _O(n)_ | _O(1)_ | Easy |馃摉|| 245| [Shortest Word Distance III](https://leetcode.com/problems/shortest-word-distance-iii/) | [C++](./C++/shortest-word-distance-iii.cpp) [Python](./Python/shortest-word-distance-iii.py) | _O(n)_ | _O(1)_ | Medium |馃摉|| 251| [Flatten 2D Vector](https://leetcode.com/problems/flatten-2d-vector/) | [C++](./C++/flatten-2d-vector.cpp) [Python](./Python/flatten-2d-vector.py) | _O(1)_ | _O(1)_ | Medium |馃摉|| 277| [Find the Celebrity](https://leetcode.com/problems/find-the-celebrity/) | [C++](./C++/find-the-celebrity.cpp) [Python](./Python/find-the-celebrity.py) | _O(n)_ | _O(1)_ | Medium |馃摉, EPI || 289| [Game of Life](https://leetcode.com/problems/game-of-life/) | [C++](./C++/game-of-life.cpp) [Python](./Python/game-of-life.py) | _O(m * n)_ | _O(1)_ | Medium ||| 293| [Flip Game](https://leetcode.com/problems/flip-game/) | [C++](./C++/flip-game.cpp) [Python](./Python/flip-game.py) | _O(n * (c+1))_ | _O(1)_ | Easy |馃摉|| 296| [Best Meeting Point](https://leetcode.com/problems/best-meeting-point/) | [C++](./C++/best-meeting-point.cpp) [Python](./Python/best-meeting-point.py) | _O(m * n)_ | _O(m + n)_ | Hard |馃摉|| 311| [Sparse Matrix Multiplication](https://leetcode.com/problems/sparse-matrix-multiplication/) | [C++](./C++/sparse-matrix-multiplication.cpp) [Python](./Python/sparse-matrix-multiplication.py) | _O(m * n * l)_ | _O(m * l)_ | Medium |馃摉|| 334| [Increasing Triplet Subsequence](https://leetcode.com/problems/increasing-triplet-subsequence/) | [C++](./C++/increasing-triplet-subsequence.cpp) [Python](./Python/increasing-triplet-subsequence.py) | _O(n)_ | _O(1)_ | Medium ||| 370| [Range Addition](https://leetcode.com/problems/range-addition/) | [C++](./C++/range-addition.cpp) [Python](./Python/range-addition.py) | _O(k + n)_ | _O(1)_ | Medium |馃摉|| 384| [Shuffle an Array](https://leetcode.com/problems/shuffle-an-array/) | [C++](./C++/shuffle-an-array.cpp) [Python](./Python/shuffle-an-array.py) | _O(n)_ | _O(n)_ | Medium | EPI || 396| [Rotate Function](https://leetcode.com/problems/rotate-function/) | [C++](./C++/rotate-function.cpp) [Python](./Python/rotate-function.py) | _O(n)_ | _O(1)_ | Easy ||| 412| [Fizz Buzz](https://leetcode.com/problems/fizz-buzz/) | [C++](./C++/fizz-buzz.cpp) [Python](./Python/fizz-buzz.py) | _O(n)_ | _O(1)_ | Easy ||| 414| [Third Maximum Number](https://leetcode.com/problems/third-maximum-number/) | [C++](./C++/third-maximum-number.cpp) [Python](./Python/third-maximum-number.py) | _O(n)_ | _O(1)_ | Easy ||| 419| [Battleships in a Board](https://leetcode.com/problems/battleships-in-a-board/) | [C++](./C++/battleships-in-a-board.cpp) [Python](./Python/battleships-in-a-board.py) | _O(m * n)_ | _O(1)_ | Medium ||| 422| [Valid Word Square](https://leetcode.com/problems/valid-word-square/) | [C++](./C++/valid-word-square.cpp) [Python](./Python/valid-word-square.py) | _O(m * n)_ | _O(1)_ | Easy |馃摉|| 442| [Find All Duplicates in an Array](https://leetcode.com/problems/find-all-duplicates-in-an-array/) | [C++](./C++/find-all-duplicates-in-an-array.cpp) [Python](./Python/find-all-duplicates-in-an-array.py) | _O(n)_ | _O(1)_ | Medium ||| 448| [Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/) | [C++](./C++/find-all-numbers-disappeared-in-an-array.cpp) [Python](./Python/find-all-numbers-disappeared-in-an-array.py) | _O(n)_ | _O(1)_ | Easy ||| ## String | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 5| [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/) | [C++](./C++/longest-palindromic-substring.cpp) [Python](./Python/longest-palindromic-substring.py) | _O(n)_ | _O(n)_ | Medium || `Manacher's Algorithm` 6| [ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/) | [C++](./C++/zigzag-conversion.cpp) [Python](./Python/zigzag-conversion.py) | _O(n)_ | _O(1)_ | Easy || 8| [String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/) | [C++](./C++/string-to-integer-atoi.cpp) [Python](./Python/string-to-integer-atoi.py) | _O(n)_ | _O(1)_ | Easy || 14| [Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/) | [C++](./C++/longest-common-prefix.cpp) [Python](./Python/longest-common-prefix.py) | _O(n * k)_ | _O(1)_ | Easy || 28| [Implement strStr()](https://leetcode.com/problems/implement-strstr/) | [C++](./C++/implement-strstr.cpp) [Python](./Python/implement-strstr.py) | _O(n + k)_ | _O(k)_ | Easy || `KMP Algorithm` 38| [Count and Say](https://leetcode.com/problems/count-and-say/) | [C++](./C++/count-and-say.cpp) [Python](./Python/count-and-say.py)| _O(n * 2^n)_ | _O(2^n)_ | Easy || 43| [Multiply Strings](https://leetcode.com/problems/multiply-strings/) | [C++](./C++/multiply-strings.cpp) [Python](./Python/multiply-strings.py) | _O(m * n)_ | _O(m + n)_ | Medium || 58| [Length of Last Word](https://leetcode.com/problems/length-of-last-word/) | [C++](./C++/length-of-last-word.cpp) [Python](./Python/length-of-last-word.py) | _O(n)_ | _O(1)_ | Easy || 67| [Add Binary](https://leetcode.com/problems/add-binary/) | [C++](./C++/add-binary.cpp) [Python](./Python/add-binary.py) | _O(n)_ | _O(1)_ | Easy || 68| [Text Justification](https://leetcode.com/problems/text-justification/) | [C++](./C++/text-justification.cpp) [Python](./Python/text-justification.py) | _O(n)_ | _O(1)_ | Hard || 125| [Valid Palindrome](https://leetcode.com/problems/valid-palindrome/) | [C++](./C++/valid-palindrome.cpp) [Python](./Python/valid-palindrome.py) | _O(n)_ | _O(1)_ | Easy || 151| [Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string/) | [C++](./C++/reverse-words-in-a-string.cpp) [Python](./Python/reverse-words-in-a-string.py) | _O(n)_ | _O(1)_ | Medium || 161| [One Edit Distance](https://leetcode.com/problems/one-edit-distance/) | [C++](./C++/one-edit-distance.cpp) [Python](./Python/one-edit-distance.py) | _O(m + n)_ | _O(1)_ | Medium |馃摉 | 165| [Compare Version Numbers](https://leetcode.com/problems/compare-version-numbers/) | [C++](./C++/compare-version-numbers.cpp) [Python](./Python/compare-version-numbers.py) | _O(n)_ | _O(1)_ | Easy || 186| [Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/) |[C++](./C++/reverse-words-in-a-string-ii.cpp) [Python](./Python/reverse-words-in-a-string-ii.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | 214| [Shortest Palindrome](https://leetcode.com/problems/shortest-palindrome/) | [C++](./C++/shortest-palindrome.cpp) [Python](./Python/shortest-palindrome.py) | _O(n)_ | _O(n)_ | Hard || `KMP Algorithm` `Manacher's Algorithm` 242| [Valid Anagram](https://leetcode.com/problems/valid-anagram/)| [C++](./C++/valid-anagram.cpp) [Python](./Python/valid-anagram.py) | _O(n)_ | _O(1)_ | Easy | LintCode | 271| [Encode and Decode Strings](https://leetcode.com/problems/encode-and-decode-strings/) | [C++](./C++/encode-and-decode-strings.cpp) [Python](./Python/encode-and-decode-strings.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | 273| [Integer to English Words](https://leetcode.com/problems/integer-to-english-words/) | [C++](./C++/integer-to-english-words.cpp) [Python](./Python/integer-to-english-words.py) | _O(logn)_ | _O(1)_ | Hard | | 306| [Addictive Number](https://leetcode.com/problems/additive-number/) | [C++](./C++/additive-number.cpp) [Python](./Python/additive-number.py) | _O(n^3)_ | _O(n)_ | Medium | | 383| [Ransom Note](https://leetcode.com/problems/ransom-note/) | [C++](./C++/ransom-note.cpp) [Python](./Python/ransom-note.py) | _O(n)_ | _O(1)_ | Easy | EPI | 405| [Convert a Number to Hexadecimal](https://leetcode.com/problems/convert-a-number-to-hexadecimal/) | [C++](./C++/convert-a-number-to-hexadecimal.cpp) [Python](./Python/convert-a-number-to-hexadecimal.py) | _O(n)_ | _O(1)_ | Easy | | 408| [Valid Word Abbreviation](https://leetcode.com/problems/valid-word-abbreviation/) | [C++](./C++/valid-word-abbreviation.cpp) [Python](./Python/valid-word-abbreviation.py) | _O(n)_ | _O(1)_ | Easy | 馃摉 | 415| [Add Strings](https://leetcode.com/problems/add-strings/) | [C++](./C++/add-strings.cpp) [Python](./Python/add-strings.py) | _O(n)_ | _O(1)_ | Easy | | 420| [Strong Password Checker](https://leetcode.com/problems/strong-password-checker/) | [C++](./C++/strong-password-checker.cpp) [Python](./Python/strong-password-checker.py) | _O(n)_ | _O(1)_ | Hard | | 434| [Number of Segments in a String](https://leetcode.com/problems/number-of-segments-in-a-string/) | [C++](./C++/number-of-segments-in-a-string.cpp) [Python](./Python/number-of-segments-in-a-string.py) | _O(n)_ | _O(1)_ | Easy | | 459| [Repeated Substring Pattern](https://leetcode.com/problems/repeated-substring-pattern/) | [C++](./C++/repeated-substring-pattern.cpp) [Python](./Python/repeated-substring-pattern.py) | _O(n)_ | _O(n)_ | Easy || `KMP Algorithm` | 468| [Validate IP Address](https://leetcode.com/problems/validate-ip-address/) | [C++](./C++/validate-ip-address.cpp) [Python](./Python/validate-ip-address.py) | _O(1)_ | _O(1)_ | Medium | | ## Linked List | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 2| [Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [C++](./C++/add-two-numbers.cpp) [Python](./Python/add-two-numbers.py) | _O(n)_ | _O(1)_ | Medium || 21| [Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)| [C++](./C++/merge-two-sorted-lists.cpp) [Python](./Python/merge-two-sorted-lists.py) | _O(n)_ | _O(1)_ | Easy || 23| [Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/) | [C++](./C++/merge-k-sorted-lists.cpp) [Python](./Python/merge-k-sorted-lists.py) | _O(nlogk)_| _O(1)_| Hard | | Heap, Divide and Conquer 24| [Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)| [C++](./C++/swap-nodes-in-pairs.cpp) [Python](./Python/swap-nodes-in-pairs.py) | _O(n)_ | _O(1)_ | Easy || 25| [Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/)| [C++](./C++/reverse-nodes-in-k-group.cpp) [Python](./Python/reverse-nodes-in-k-group.py) | _O(n)_ | _O(1)_ | Hard || 61| [Rotate List](https://leetcode.com/problems/rotate-list/)| [C++](./C++/rotate-list.cpp) [Python](./Python/rotate-list.py) | _O(n)_ | _O(1)_ | Medium || 82| [Remove Duplicates from Sorted List II](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/)| [C++](./C++/remove-duplicates-from-sorted-list-ii.cpp) [Python](./Python/remove-duplicates-from-sorted-list-ii.py) | _O(n)_ | _O(1)_ | Medium || 83| [Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list/)| [C++](./C++/remove-duplicates-from-sorted-list.cpp) [Python](./Python/remove-duplicates-from-sorted-list.py) | _O(n)_ | _O(1)_ | Easy || 92| [Reverse Linked List II](https://leetcode.com/problems/reverse-linked-list-ii/)| [C++](./C++/reverse-linked-list-ii.cpp) [Python](./Python/reverse-linked-list-ii.py) | _O(n)_ | _O(1)_ | Medium || 138| [Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer/) | [C++](./C++/copy-list-with-random-pointer.cpp) [Python](./Python/copy-list-with-random-pointer.py) | _O(n)_ | _O(1)_ | Hard || 160| [Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists/)| [C++](./C++/intersection-of-two-linked-lists.cpp) [Python](./Python/intersection-of-two-linked-lists.py) | _O(m + n)_ | _O(1)_ | Easy || 203| [Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/)| [C++](./C++/remove-linked-list-elements.cpp) [Python](./Python/remove-linked-list-elements.py) | _O(n)_ | _O(1)_ | Easy || 206| [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)| [C++](./C++/reverse-linked-list.cpp) [Python](./Python/reverse-linked-list.py) | _O(n)_ | _O(1)_ | Easy || 234| [Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/)| [C++](./C++/palindrome-linked-list.cpp) [Python](./Python/palindrome-linked-list.py) | _O(n)_ | _O(1)_ | Easy || 237| [Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list/)| [C++](./C++/delete-node-in-a-linked-list.cpp) [Python](./Python/delete-node-in-a-linked-list.py) | _O(1)_ | _O(1)_ | Easy | LintCode | 328| [Odd Even Linked List](https://leetcode.com/problems/odd-even-linked-list/)| [C++](./C++/odd-even-linked-list.cpp) [Python](./Python/odd-even-linked-list.py) | _O(n)_ | _O(1)_ | Medium | | 369| [Plus One Linked List](https://leetcode.com/problems/plus-one-linked-list/)| [C++](./C++/plus-one-linked-list.cpp) [Python](./Python/plus-one-linked-list.py) | _O(n)_ | _O(1)_ | Medium | 馃摉 | Two Pointers | 445| [Add Two Numbers II](https://leetcode.com/problems/add-two-numbers-ii/)| [C++](./C++/add-two-numbers-ii.cpp) [Python](./Python/add-two-numbers-ii.py) | _O(m + n)_ | _O(m + n)_ | Medium ||| ## Stack | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 20| [Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| [C++](./C++/valid-parentheses.cpp) [Python](./Python/valid-parentheses.py) | _O(n)_ | _O(n)_ | Easy || 32| [Longest Valid Parentheses](https://leetcode.com/problems/longest-valid-parentheses/)| [C++](./C++/longest-valid-parentheses.cpp) [Python](./Python/longest-valid-parentheses.py) | _O(n)_ | _O(1)_ | Hard || 71| [Simplify Path](https://leetcode.com/problems/simplify-path/)| [C++](./C++/simplify-path.cpp) [Python](./Python/simplify-path.py) | _O(n)_ | _O(n)_ | Medium || 84| [Largest Rectangle in Histogram](https://leetcode.com/problems/largest-rectangle-in-histogram/) | [C++](./C++/largest-rectangle-in-histogram.cpp) [Python](./Python/largest-rectangle-in-histogram.py) | _O(n)_ | _O(n)_ | Hard || Ascending Stack, DP 85| [Maximal Rectangle](https://leetcode.com/problems/maximal-rectangle/)| [C++](./C++/maximal-rectangle.cpp) [Python](./Python/maximal-rectangle.py)| _O(m * n)_ | _O(n)_ | Hard | EPI | Ascending Stack 101| [Symmetric Tree](https://leetcode.com/problems/symmetric-tree/)| [C++](./C++/symmetric-tree.cpp) [Python](./Python/symmetric-tree.py) | _O(n)_ | _O(h)_ | Easy || 150| [Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/)| [C++](./C++/evaluate-reverse-polish-notation.cpp) [Python](./Python/evaluate-reverse-polish-notation.py)| _O(n)_| _O(n)_| Medium || 155| [Min Stack](https://leetcode.com/problems/min-stack/) | [C++](./C++/min-stack.cpp) [Python](./Python/min-stack.py) | _O(n)_ | _O(1)_ | Easy || 173| [Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/) | [C++](./C++/binary-search-tree-iterator.cpp) [Python](./Python/binary-search-tree-iterator.py) | _O(1)_| _O(h)_| Medium || 224| [Basic Calculator](https://leetcode.com/problems/basic-calculator/) | [C++](./C++/basic-calculator.cpp) [Python](./Python/basic-calculator.py) | _O(n)_| _O(n)_| Hard || 227| [Basic Calculator II](https://leetcode.com/problems/basic-calculator-ii/) | [C++](./C++/basic-calculator-ii.cpp) [Python](./Python/basic-calculator-ii.py) | _O(n)_| _O(n)_| Medium || 232| [Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/) | [C++](./C++/implement-queue-using-stacks.cpp) [Python](./Python/implement-queue-using-stacks.py) | _O(1), amortized_| _O(n)_| Easy | EPI, LintCode | 255| [Verify Preorder Sequence in Binary Search Tree](https://leetcode.com/problems/verify-preorder-sequence-in-binary-search-tree/) | [C++](./C++/verify-preorder-sequence-in-binary-search-tree.cpp) [Python](./Python/verify-preorder-sequence-in-binary-search-tree.py) | _O(n)_| _O(1)_| Medium |馃摉|| 272| [Closest Binary Search Tree Value II](https://leetcode.com/problems/closest-binary-search-tree-value-ii/) | [C++](./C++/closest-binary-search-tree-value-ii.cpp) [Python](./Python/closest-binary-search-tree-value-ii.py) | _O(h + k)_| _O(h)_| Hard |馃摉|| 331| [Verify Preorder Serialization of a Binary Tree](https://leetcode.com/problems/verify-preorder-serialization-of-a-binary-tree/) | [C++](./C++/verify-preorder-serialization-of-a-binary-tree.cpp) [Python](./Python/verify-preorder-serialization-of-a-binary-tree.py) | _O(n)_| _O(1)_| Medium ||| 341| [Flatten Nested List Iterator](https://leetcode.com/problems/flatten-nested-list-iterator/)| [C++](./C++/flatten-nested-list-iterator.cpp) [Python](./Python/flatten-nested-list-iterator.py) | _O(n)_ | _O(h)_ | Medium |馃摉| Iterator | 385| [Mini Parser](https://leetcode.com/problems/mini-parser/)| [C++](./C++/mini-parser.cpp) [Python](./Python/mini-parser.py) | _O(n)_ | _O(h)_ | Medium ||| 394| [Decode String](https://leetcode.com/problems/decode-string/)| [C++](./C++/decode-string.cpp) [Python](./Python/decode-string.py) | _O(n)_ | _O(h)_ | Medium ||| 439| [Ternary Expression Parser](https://leetcode.com/problems/ternary-expression-parser/) | [C++](./C++/ternary-expression-parser.cpp) [Python](./Python/ternary-expression-parser.py) | _O(n)_ | _O(1)_ | Medium |馃摉| 456| [132 Pattern](https://leetcode.com/problems/132-pattern/) | [C++](./C++/132-pattern.cpp) [Python](./Python/132-pattern.py) | _O(n)_ | _O(n)_ | Medium || ## Queue | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 239| [Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum/)| [C++](./C++/sliding-window-maximum.cpp) [Python](./Python/sliding-window-maximum.py) | _O(n)_ | _O(k)_ | Hard | EPI, LintCode | 281| [Zigzag Iterator](https://leetcode.com/problems/zigzag-iterator/)| [C++](./C++/zigzag-iterator.cpp) [Python](./Python/zigzag-iterator.py) | _O(n)_ | _O(k)_ | Medium |馃摉|| 346| [Moving Average from Data Stream](https://leetcode.com/problems/moving-average-from-data-stream/)| [C++](./C++/moving-average-from-data-stream.cpp) [Python](./Python/moving-average-from-data-stream.py) | _O(1)_ | _O(w)_ | Easy |馃摉|| ## Heap | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 264| [Ugly Number II](https://leetcode.com/problems/ugly-number-ii/) | [C++](./C++/ugly-number-ii.cpp) [Python](./Python/ugly-number-ii.py) | _O(n)_ | _O(1)_ | Medium | CTCI, LintCode | BST, Heap | 295| [Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/) | [C++](./C++/find-median-from-data-stream.cpp) [Python](./Python/find-median-from-data-stream.py) | _O(nlogn)_ | _O(n)_ | Hard | EPI, LintCode | BST, Heap | 313| [Super Ugly Number](https://leetcode.com/problems/super-ugly-number/) | [C++](./C++/super-ugly-number.cpp) [Python](./Python/super-ugly-number.py) | _O(n * k)_ | _O(n + k)_ | Medium || BST, Heap | 358| [Rearrange String k Distance Apart](https://leetcode.com/problems/rearrange-string-k-distance-apart/)| [C++](./C++/rearrange-string-k-distance-apart.cpp) [Python](./Python/rearrange-string-k-distance-apart.py) | _O(n)_ | _O(n)_ | Hard |馃摉| Greedy, Heap | 373 | [Find K Pairs with Smallest Sums](https://leetcode.com/problems/find-k-pairs-with-smallest-sums/) | [C++](./C++/find-k-pairs-with-smallest-sums.cpp) [Python](./Python/find-k-pairs-with-smallest-sums.py) | _O(k * log(min(n, m, k)))_ | _O(min(n, m, k))_ | Medium ||| 378 | [Kth Smallest Element in a Sorted Matrix](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/) | [C++](./C++/kth-smallest-element-in-a-sorted-matrix.cpp) [Python](./Python/kth-smallest-element-in-a-sorted-matrix.py) | _O(k * log(min(n, m, k)))_ | _O(min(n, m, k))_ | Medium | LintCode || 407 | [Trapping Rain Water II](https://leetcode.com/problems/trapping-rain-water-ii/) | [C++](./C++/trapping-rain-water-ii.cpp) [Python](./Python/trapping-rain-water-ii.py) | _O(m * n * (logm + logn))_ | _O(m * n)_ | Hard | LintCode || ## Tree | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 94 | [Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/) | [C++](./C++/binary-tree-inorder-traversal.cpp) [Python](./Python/binary-tree-inorder-traversal.py) | _O(n)_| _O(1)_| Medium || `Morris Traversal` | 99 | [Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree/) | [C++](./C++/recover-binary-search-tree.cpp) [Python](./Python/recover-binary-search-tree.py) | _O(n)_| _O(1)_| Hard || `Morris Traversal` 144 | [Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/) | [C++](./C++/binary-tree-preorder-traversal.cpp) [Python](./Python/binary-tree-preorder-traversal.py) | _O(n)_| _O(1)_| Medium || `Morris Traversal` 145 | [Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal/) | [C++](./C++/binary-tree-postorder-traversal.cpp) [Python](./Python/binary-tree-postorder-traversal.py) | _O(n)_| _O(1)_| Hard || `Morris Traversal` 208 | [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/) | [C++](./C++/implement-trie-prefix-tree.cpp) [Python](./Python/implement-trie-prefix-tree.py) | _O(n)_ | _O(1)_ | Medium || Trie 211 | [Add and Search Word - Data structure design](https://leetcode.com/problems/add-and-search-word-data-structure-design/) | [C++](./C++/add-and-search-word-data-structure-design.cpp) [Python](./Python/add-and-search-word-data-structure-design.py) | _O(min(n, h))_ | _O(min(n, h))_ | Medium || Trie, DFS 226| [Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/) | [C++](./C++/invert-binary-tree.cpp) [Python](./Python/invert-binary-tree.py) | _O(n)_ | _O(h)_, _O(w)_ | Easy || 297 | [Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) | [C++](./C++/serialize-and-deserialize-binary-tree.cpp) [Python](./Python/serialize-and-deserialize-binary-tree.py) | _O(n)_ | _O(h)_ | Hard | LintCode | DFS 307 | [Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/) | [C++](./C++/range-sum-query-mutable.cpp) [Python](./Python/range-sum-query-mutable.py) | ctor: _O(n)_, update: _O(logn)_, query: _O(logn)_ | _O(n)_ | Medium | LintCode | DFS, Segment Tree, BIT 308 | [Range Sum Query 2D - Mutable](https://leetcode.com/problems/range-sum-query-2d-mutable/) | [C++](./C++/range-sum-query-2d-mutable.cpp) [Python](./Python/range-sum-query-2d-mutable.py) | ctor: _O(m * n)_, update: _O(logm + logn)_, query: _O(logm + logn)_ | _O(m * n)_ | Hard | 馃摉 | DFS, Segment Tree, BIT 315|[Count of Smaller Numbers After Self](https://leetcode.com/problems/count-of-smaller-numbers-after-self/)| [C++](./C++/count-of-smaller-numbers-after-self.cpp) [Python](./Python/count-of-smaller-numbers-after-self.py)| _O(nlogn)_ | _O(n)_ | Hard | LintCode | BST, BIT, Divide and Conquer | ## Hash Table | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 1| [Two Sum](https://leetcode.com/problems/two-sum/) | [C++](./C++/two-sum.cpp) [Python](./Python/two-sum.py) | _O(n)_ | _O(n)_ | Easy || 3| [Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [C++](./C++/longest-substring-without-repeating-characters.cpp) [Python](./Python/longest-substring-without-repeating-characters.py) | _O(n)_ | _O(1)_ | Medium || 30| [Substring with Concatenation of All Words](https://leetcode.com/problems/substring-with-concatenation-of-all-words/) | [C++](./C++/substring-with-concatenation-of-all-words.cpp) [Python](./Python/substring-with-concatenation-of-all-words.py) | _O(m * n * k)_ | _O(n * k)_ | Hard || 36| [Valid Sudoku](https://leetcode.com/problems/valid-sudoku/) | [C++](./C++/valid-sudoku.cpp) [Python](./Python/valid-sudoku.py) | _O(9^2)_ | _O(9)_ | Easy || 49| [Group Anagrams](https://leetcode.com/problems/anagrams/) | [C++](./C++/anagrams.cpp) [Python](./Python/anagrams.py) | _O(n * glogg)_ | _O(n)_ | Medium || 76| [Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/) | [C++](./C++/minimum-window-substring.cpp) [Python](./Python/minimum-window-substring.py) | _O(n)_ | _O(k)_ | Hard || 149| [Max Points on a Line](https://leetcode.com/problems/max-points-on-a-line/) | [C++](./C++/max-points-on-a-line.cpp) [Python](./Python/max-points-on-a-line.py) | _O(n^2)_ | _O(n)_ | Hard || 159| [Longest Substring with At Most Two Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/)| [C++](./C++/longest-substring-with-at-most-two-distinct-characters.cpp) [Python](./Python/longest-substring-with-at-most-two-distinct-characters.py) | _O(n)_ | _O(1)_ | Hard |馃摉| 170| [Two Sum III - Data structure design](https://leetcode.com/problems/two-sum-iii-data-structure-design/) | [C++](./C++/two-sum-iii-data-structure-design.cpp) [Python](./Python/two-sum-iii-data-structure-design.py) | _O(n)_ | _O(n)_ | Easy | 馃摉 | 187| [Repeated DNA Sequences](https://leetcode.com/problems/repeated-dna-sequences/) | [Python](./Python/repeated-dna-sequences.py) | _O(n)_ | _O(n)_ | Medium || 202| [Happy Number](https://leetcode.com/problems/happy-number/) | [C++](./C++/happy-number.cpp) [Python](./Python/happy-number.py) | _O(k)_ | _O(k)_ | Easy || 204| [Count Primes](https://leetcode.com/problems/count-primes/) | [C++](./C++/count-primes.cpp) [Python](./Python/count-primes.py) | _O(n)_ | _O(n)_ | Easy || 205| [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/) | [C++](./C++/isomorphic-strings.cpp) [Python](./Python/isomorphic-strings.py) | _O(n)_ | _O(1)_ | Easy || 217| [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/) | [C++](./C++/contains-duplicate.cpp) [Python](./Python/contains-duplicate.py) | _O(n)_ | _O(n)_ | Easy || 219| [Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/) | [C++](./C++/contains-duplicate-ii.cpp) [Python](./Python/contains-duplicate-ii.py) | _O(n)_ | _O(n)_ | Easy || 244| [Shortest Word Distance II](https://leetcode.com/problems/shortest-word-distance-ii/) | [C++](./C++/shortest-word-distance-ii.cpp) [Python](./Python/shortest-word-distance-ii.py) | ctor: _O(n)_, lookup: _O(a + b)_ | _O(n)_ | Medium |馃摉|| 246| [Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/) | [C++](./C++/strobogrammatic-number.cpp) [Python](./Python/strobogrammatic-number.py) | _O(n)_ | _O(1)_ | Easy |馃摉|| 249| [Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/) | [C++](./C++/group-shifted-strings.cpp) [Python](./Python/group-shifted-strings.py) | _O(nlogn)_ | _O(n)_ | Easy |馃摉|| 266| [Palindrome Permutation](https://leetcode.com/problems/palindrome-permutation/) | [C++](./C++/palindrome-permutation.cpp) [Python](./Python/palindrome-permutation.py) | _O(n)_ | _O(1)_ | Easy |馃摉|| 288| [Unique Word Abbreviation](https://leetcode.com/problems/unique-word-abbreviation/) | [C++](./C++/unique-word-abbreviation.cpp) [Python](./Python/unique-word-abbreviation.py) | ctor: _O(n)_, lookup: _O(1)_ | _O(k)_ | Easy |馃摉|| 290| [Word Pattern](https://leetcode.com/problems/word-pattern/) | [C++](./C++/word-pattern.cpp) [Python](./Python/word-pattern.py) | _O(n)_ | _O(c)_ | Easy | variant of [Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/) || 299| [Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/) | [C++](./C++/bulls-and-cows.cpp) [Python](./Python/bulls-and-cows.py) | _O(n)_ | _O(1)_ | Easy ||| 305| [Number of Islands II](https://leetcode.com/problems/number-of-islands-ii/) | [C++](./C++/number-of-islands-ii.cpp) [Python](./Python/number-of-islands-ii.py) | _O(k)_ | _O(k)_| Hard | LintCode, 馃摉 | Union Find 314| [Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/) | [C++](./C++/binary-tree-vertical-order-traversal.cpp) [Python](./Python/binary-tree-vertical-order-traversal.py) | _O(n)_ | _O(n)_| Medium | 馃摉 | BFS 323| [Number of Connected Components in an Undirected Graph](https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/) | [C++](./C++/number-of-connected-components-in-an-undirected-graph.cpp) [Python](./Python/number-of-connected-components-in-an-undirected-graph.py) | _O(n)_ | _O(n)_| Medium | 馃摉 | Union Find 325| [Maximum Size Subarray Sum Equals k](https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/) | [C++](./C++/maximum-size-subarray-sum-equals-k.cpp) [Python](./Python/maximum-size-subarray-sum-equals-k.py) | _O(n)_ | _O(n)_| Medium | 馃摉 | 336| [Palindrome Pairs](https://leetcode.com/problems/palindrome-pairs/) | [C++](./C++/palindrome-pairs.cpp) [Python](./Python/palindrome-pairs.py) | _O(n * k^2)_ | _O(n * k)_ | Hard | | | 340| [Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/)| [C++](./C++/longest-substring-with-at-most-k-distinct-characters.cpp) [Python](./Python/longest-substring-with-at-most-k-distinct-characters.py) | _O(n)_ | _O(1)_ | Hard |馃摉| 356| [Line Reflection](https://leetcode.com/problems/line-reflection/) | [C++](./C++/line-reflection.cpp) [Python](./Python/line-reflection.py) | _O(n)_| _O(n)_| Medium |馃摉| Hash, Two Pointers | 387| [First Unique Character in a String](https://leetcode.com/problems/first-unique-character-in-a-string/) | [C++](./C++/first-unique-character-in-a-string.cpp) [Python](./Python/first-unique-character-in-a-string.py) | _O(n)_| _O(n)_| Easy ||| 388| [Longest Absolute File Path](https://leetcode.com/problems/longest-absolute-file-path/) | [C++](./C++/longest-absolute-file-path.cpp) [Python](./Python/longest-absolute-file-path.py) | _O(n)_| _O(d)_| Medium || Stack | 409| [Longest Palindrome](https://leetcode.com/problems/longest-palindrome/) | [C++](./C++/longest-palindrome.cpp) [Python](./Python/longest-palindrome.py) | _O(n)_| _O(1)_| Easy ||| 424| [Longest Repeating Character Replacement](https://leetcode.com/problems/longest-repeating-character-replacement/) | [C++](./C++/longest-repeating-character-replacement.cpp) [Python](./Python/longest-repeating-character-replacement.py) | _O(n)_| _O(1)_| Medium ||| 438| [Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/) | [C++](./C++/find-all-anagrams-in-a-string.cpp) [Python](./Python/find-all-anagrams-in-a-string.py) | _O(n)_ | _O(1)_ | Easy || 447| [Number of Boomerangs](https://leetcode.com/problems/number-of-boomerangs/) | [C++](./C++/number-of-boomerangs.cpp) [Python](./Python/number-of-boomerangs.py) | _O(n^2)_ | _O(n)_ | Easy || 454| [4Sum II](https://leetcode.com/problems/4sum-ii/) | [C++](./C++/4sum-ii.cpp) [Python](./Python/4sum-ii.py) | _O(n^2)_ | _O(n^2)_ | Medium || 473| [Matchsticks to Square](https://leetcode.com/problems/matchsticks-to-square/) | [C++](./C++/matchsticks-to-square.cpp) [Python](./Python/matchsticks-to-square.py) | _O(n * s * 2^n)_ | _O(n * (2^n + s))_ | Medium || ## Data Structure | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 146| [LRU Cache](https://leetcode.com/problems/lru-cache/) | [C++](./C++/lru-cache.cpp) [Python](./Python/lru-cache.py) | _O(1)_ | _O(k)_ | Hard || 225| [Implement Stack using Queues](https://leetcode.com/problems/implement-stack-using-queues/) | [C++](./C++/implement-stack-using-queues.cpp) [Python](./Python/implement-stack-using-queues.py) | push: _O(n)_, pop: _O(1)_, top: _O(1)_ | _O(n)_ | Easy || ## Math | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 7| [Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [C++](./C++/reverse-integer.cpp) [Python](./Python/reverse-integer.py) | _O(1)_ | _O(1)_ | Easy || 9| [Palindrome Number](https://leetcode.com/problems/palindrome-number/) | [C++](./C++/palindrome-number.cpp) [Python](./Python/palindrome-number.py) | _O(1)_ | _O(1)_ | Easy || 12| [Integer to Roman](https://leetcode.com/problems/integer-to-roman/) | [C++](./C++/integer-to-roman.cpp) [Python](./Python/integer-to-roman.py) | _O(n)_ | _O(1)_ | Medium || 13| [Roman to Integer](https://leetcode.com/problems/roman-to-integer/) | [C++](./C++/roman-to-integer.cpp) [Python](./Python/roman-to-integer.py) | _O(n)_ | _O(1)_ | Easy || 29| [Divide Two Integers](https://leetcode.com/problems/divide-two-integers/) | [C++](./C++/divide-two-integers.cpp) [Python](./Python/divide-two-integers.py) | _O(1)_ | _O(1)_ | Medium || 50| [Pow(x, n)](https://leetcode.com/problems/powx-n/) | [C++](./C++/powx-n.cpp) [Python](./Python/powx-n.py) | _O(1)_ | _O(1)_ | Medium || 60| [Permutation Sequence](https://leetcode.com/problems/permutation-sequence/) | [C++](./C++/permutation-sequence.cpp) [Python](./Python/permutation-sequence.py) | _O(n^2)_ | _O(n)_ | Medium || `Cantor Ordering` 65| [Valid Number](https://leetcode.com/problems/valid-number/) | [C++](./C++/valid-number.cpp) [Python](./Python/valid-number.py) | _O(n)_ | _O(1)_ | Hard || `Automata` 89| [Gray Code](https://leetcode.com/problems/gray-code/) | [C++](./C++/gray-code.cpp) [Python](./Python/gray-code.py) | _O(2^n)_ | _O(1)_ | Medium || 166| [Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal/) | [C++](./C++/fraction-to-recurring-decimal.cpp) [Python](./Python/fraction-to-recurring-decimal.py) | _O(logn)_ | _O(1)_ | Medium || 168| [Excel Sheet Column Title](https://leetcode.com/problems/excel-sheet-column-title/) | [C++](./C++/excel-sheet-column-title.cpp) [Python](./Python/excel-sheet-column-title.py) | _O(logn)_ | _O(1)_ | Easy || 171| [Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number/) | [C++](./C++/excel-sheet-column-number.cpp) [Python](./Python/excel-sheet-column-number.py) | _O(n)_ | _O(1)_ | Easy || 172| [Factorial Trailing Zeroes](https://leetcode.com/problems/factorial-trailing-zeroes/) | [C++](./C++/factorial-trailing-zeroes.cpp) [Python](./Python/factorial-trailing-zeroes.py) | _O(1)_ | _O(1)_ | Easy || 223| [Rectangle Area](https://leetcode.com/problems/rectangle-area/) | [C++](./C++/rectangle-area.cpp) [Python](./Python/rectangle-area.py) | _O(1)_ | _O(1)_ | Easy || 233| [Number of Digit One](https://leetcode.com/problems/number-of-digit-one/) | [C++](./C++/number-of-digit-one.cpp) [Python](./Python/number-of-digit-one.py) | _O(1)_ | _O(1)_ | Hard | CTCI, LintCode| 248| [Strobogrammatic Number III](https://leetcode.com/problems/strobogrammatic-number-iii/) | [C++](./C++/strobogrammatic-number-iii.cpp) [Python](./Python/strobogrammatic-number-iii.py) | _O(5^(n/2))_ | _O(n)_ | Hard |馃摉|| 258| [Add Digits](https://leetcode.com/problems/add-digits/) | [C++](./C++/add-digits.cpp) [Python](./Python/add-digits.py) | _O(1)_ | _O(1)_ | Easy ||| 263| [Ugly Number](https://leetcode.com/problems/ugly-number/) | [C++](./C++/ugly-number.cpp) [Python](./Python/ugly-number.py) | _O(1)_ | _O(1)_ | Easy ||| 292| [Nim Game](https://leetcode.com/problems/nim-game/) | [C++](./C++/nim-game.cpp) [Python](./Python/nim-game.py) | _O(1)_ | _O(1)_ | Easy | LintCode || 319 | [Bulb Switcher](https://leetcode.com/problems/bulb-switcher/) | [C++](./C++/bulb-switcher.cpp) [Python](./Python/bulb-switcher.py) | _O(1)_ | _O(1)_ | Medium ||| 326 | [Power of Three](https://leetcode.com/problems/power-of-three/) | [C++](./C++/power-of-three.cpp) [Python](./Python/power-of-three.py) | _O(1)_ | _O(1)_ | Easy ||| 335 | [Self Crossing](https://leetcode.com/problems/self-crossing/) | [C++](./C++/self-crossing.cpp) [Python](./Python/self-crossing.py) | _O(n)_ | _O(1)_ | Hard ||| 338 | [Counting Bits](https://leetcode.com/problems/counting-bits/) | [C++](./C++/counting-bits.cpp) [Python](./Python/counting-bits.py) | _O(n)_ | _O(n)_ | Medium ||| 343 | [Integer Break](https://leetcode.com/problems/integer-break/) | [C++](./C++/integer-break.cpp) [Python](./Python/integer-break.py) | _O(logn)_ | _O(1)_ | Medium || Tricky, DP | 365 | [Water and Jug Problem](https://leetcode.com/problems/water-and-jug-problem/) | [C++](./C++/water-and-jug-problem.cpp) [Python](./Python/water-and-jug-problem.py) | _O(logn)_ | _O(1)_ | Medium || Euclidean Algorithm | 372 | [Super Pow](https://leetcode.com/problems/super-pow/) | [C++](./C++/super-pow.cpp) [Python](./Python/super-pow.py) | _O(n)_ | _O(1)_ | Medium ||| 382 | [Linked List Random Node](https://leetcode.com/problems/linked-list-random-node/) | [C++](./C++/linked-list-random-node.cpp) [Python](./Python/linked-list-random-node.py) | _O(n)_ | _O(1)_ | Medium || `Reservoir Sampling` | 386 | [Lexicographical Numbers](https://leetcode.com/problems/lexicographical-numbers/) | [C++](./C++/lexicographical-numbers.cpp) [Python](./Python/lexicographical-numbers.py) | _O(n)_ | _O(1)_ | Medium ||| 390 | [Elimination Game](https://leetcode.com/problems/elimination-game/) | [C++](./C++/elimination-game.cpp) [Python](./Python/elimination-game.py) | _O(logn)_ | _O(1)_ | Medium || 391 | [Perfect Rectangle](https://leetcode.com/problems/perfect-rectangle/) | [C++](./C++/perfect-rectangle.cpp) [Python](./Python/perfect-rectangle.py) | _O(n)_ | _O(n)_ | Hard | | 398 | [Random Pick Index](https://leetcode.com/problems/random-pick-index/) | [C++](./C++/random-pick-index.cpp) [Python](./Python/random-pick-index.py) | _O(n)_ | _O(1)_ | Medium || `Reservoir Sampling` | 400 | [Nth Digit](https://leetcode.com/problems/nth-digit/) | [C++](./C++/nth-digit.cpp) [Python](./Python/nth-digit.py) | _O(logn)_ | _O(1)_ | Easy ||| 413 | [Arithmetic Slices](https://leetcode.com/problems/arithmetic-slices/) | [C++](./C++/arithmetic-slices.cpp) [Python](./Python/arithmetic-slices.py) | _O(n)_ | _O(1)_ | Medium ||| 423 | [Reconstruct Original Digits from English](https://leetcode.com/problems/reconstruct-original-digits-from-english/) | [C++](./C++/reconstruct-original-digits-from-english.cpp) [Python](./Python/reconstruct-original-digits-from-english.py) | _O(n)_ | _O(1)_ | Medium | [GCJ2016 - Round 1B](https://code.google.com/codejam/contest/11254486/dashboard#s=p0)|| 441 | [Arranging Coins](https://leetcode.com/problems/arranging-coins/) | [C++](./C++/arranging-coins.cpp) [Python](./Python/arranging-coins.py) | _O(nlogn)_ | _O(1)_ | Easy || Binary Search| 453 | [Minimum Moves to Equal Array Elements](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/) | [C++](./C++/minimum-number-of-arrows-to-burst-balloons.cpp) [Python](./Python/minimum-number-of-arrows-to-burst-balloons.py) | _O(n)_ | _O(1)_ | Easy ||| 458 | [Poor Pigs](https://leetcode.com/problems/poor-pigs/) | [C++](./C++/poor-pigs.cpp) [Python](./Python/poor-pigs.py) | _O(n)_ | _O(1)_ | Easy ||| 469 | [Convex Polygon](https://leetcode.com/problems/convex-polygon/) | [C++](./C++/convex-polygon.cpp) [Python](./Python/convex-polygon.py) | _O(n)_ | _O(1)_ | Medium |馃摉|| ## Sort | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 56| [Merge Intervals](https://leetcode.com/problems/merge-intervals/)| [C++](./C++/merge-intervals.cpp) [Python](./Python/merge-intervals.py) | _O(nlogn)_ | _O(1)_ | Hard || 57| [Insert Interval](https://leetcode.com/problems/insert-interval/)| [C++](./C++/insert-interval.cpp) [Python](./Python/insert-interval.py) | _O(n)_ | _O(1)_ | Hard || 75| [Sort Colors](https://leetcode.com/problems/sort-colors/) | [C++](./C++/sort-colors.cpp) [Python](./Python/sort-colors.py) | _O(n)_ | _O(1)_ | Medium || Tri Partition 88| [Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array/)| [C++](./C++/merge-sorted-array.cpp) [Python](./Python/merge-sorted-array.py) | _O(n)_ | _O(1)_ | Easy || 147| [Insertion Sort List](https://leetcode.com/problems/insertion-sort-list/)|[C++](./C++/insertion-sort-list.cpp) [Python](./Python/insertion-sort-list.py) | _O(n^2)_ | _O(1)_ | Medium || 148| [Sort List](https://leetcode.com/problems/sort-list/) | [C++](./C++/sort-list.cpp) [Python](./Python/sort-list.py) | _O(nlogn)_ | _O(logn)_ | Medium || 164| [Maximum Gap](https://leetcode.com/problems/maximum-gap/) | [C++](./C++/maximum-gap.cpp) [Python](./Python/maximum-gap.py)| _O(n)_ | _O(n)_ | Hard || Tricky 179| [Largest Number](https://leetcode.com/problems/largest-number/) | [C++](./C++/largest-number.cpp) [Python](./Python/largest-number.py) | _O(nlogn)_ | _O(1)_ | Medium || 218| [The Skyline Problem](https://leetcode.com/problems/the-skyline-problem/) | [C++](./C++/the-skyline-problem.cpp) [Python](./Python/the-skyline-problem.py) | _O(nlogn)_ | _O(n)_ | Hard || Sort, BST| 252| [Meeting Rooms](https://leetcode.com/problems/meeting-rooms/) | [C++](./C++/meeting-rooms.cpp) [Python](./Python/meeting-rooms.py) | _O(nlogn)_ | _O(n)_ | Easy |馃摉| | 253| [Meeting Rooms II](https://leetcode.com/problems/meeting-rooms-ii/) | [C++](./C++/meeting-rooms-ii.cpp) [Python](./Python/meeting-rooms-ii.py) | _O(nlogn)_ | _O(n)_ | Medium |馃摉| | 274| [H-Index](https://leetcode.com/problems/h-index/) | [C++](./C++/h-index.cpp) [Python](./Python/h-index.py) | _O(n)_ | _O(n)_ | Medium || Counting Sort | 280| [Wiggle Sort](https://leetcode.com/problems/wiggle-sort/) | [C++](./C++/wiggle-sort.cpp) [Python](./Python/wiggle-sort.py) | _O(n)_ | _O(1)_ | Medium |馃摉| | 324| [Wiggle Sort II](https://leetcode.com/problems/wiggle-sort-ii/) | [C++](./C++/wiggle-sort-ii.cpp) [Python](./Python/wiggle-sort-ii.py) | _O(n)_ on average | _O(1)_ | Medium | variant of [Sort Colors](https://leetcode.com/problems/sort-colors/) | Tri Partition | 347| [Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/) | [C++](./C++/top-k-frequent-elements.cpp) [Python](./Python/top-k-frequent-elements.py) | _O(n)_ on average | _O(n)_ | Medium | | Quick Select, Heap | 406| [Queue Reconstruction by Height](https://leetcode.com/problems/queue-reconstruction-by-height/) | [C++](./C++/queue-reconstruction-by-height.cpp) [Python](./Python/queue-reconstruction-by-height.py) | _O(n * sqrt(n))_ | _O(n)_ | Medium | | | 451| [Sort Characters By Frequency](https://leetcode.com/problems/sort-characters-by-frequency/) | [C++](./C++/sort-characters-by-frequency.cpp) [Python](./Python/sort-characters-by-frequency.py) | _O(n)_ | _O(n)_ | Medium | | | ## Two Pointers | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 19| [Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)| [C++](./C++/remove-nth-node-from-end-of-list.cpp) [Python](./Python/remove-nth-node-from-end-of-list.py) | _O(n)_ | _O(1)_ | Easy || 86| [Partition List](https://leetcode.com/problems/partition-list/)| [C++](./C++/partition-list.cpp) [Python](./Python/partition-list.py) | _O(n)_ | _O(1)_ | Medium || 141| [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/)| [C++](./C++/linked-list-cycle.cpp) [Python](./Python/linked-list-cycle.py) | _O(n)_ | _O(1)_ | Easy || 142| [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/)| [C++](./C++/linked-list-cycle-ii.cpp) [Python](./Python/linked-list-cycle-ii.py) | _O(n)_ | _O(1)_ | Medium || 143| [Reorder List](https://leetcode.com/problems/reorder-list/)| [C++](./C++/reorder-list.cpp) [Python](./Python/reorder-list.py) | _O(n)_ | _O(1)_ | Medium || 167| [Two Sum II - Input array is sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/) | [C++](./C++/two-sum-ii-input-array-is-sorted.cpp) [Python](./Python/two-sum-ii-input-array-is-sorted.py) | _O(n)_ | _O(1)_ | Medium | | 259 | [3Sum Smaller](https://leetcode.com/problems/3sum-smaller/) | [C++](./C++/3sum-smaller.cpp) [Python](./Python/3sum-smaller.py) | _O(n^2)_ | _O(1)_ | Medium | 馃摉, LintCode | 283 | [Move Zeroes](https://leetcode.com/problems/move-zeroes/) | [C++](./C++/move-zeroes.cpp) [Python](./Python/move-zeroes.py) | _O(n)_ | _O(1)_ | Easy | | 287| [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)| [C++](./C++/find-the-duplicate-number.cpp) [Python](./Python/find-the-duplicate-number.py) | _O(n)_ | _O(1)_ | Hard | | Binary Search, Two Pointers | 344| [Reverse String](https://leetcode.com/problems/reverse-string/) | [C++](./C++/reverse-string.cpp) [Python](./Python/reverse-string.py) | _O(n)_ | _O(1)_ | Easy | | 345| [Reverse Vowels of a String](https://leetcode.com/problems/reverse-vowels-of-a-string/) | [C++](./C++/reverse-vowels-of-a-string.cpp) [Python](./Python/reverse-vowels-of-a-string.py) | _O(n)_ | _O(1)_ | Easy | | 349| [Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/) | [C++](./C++/intersection-of-two-arrays.cpp) [Python](./Python/intersection-of-two-arrays.py) | _O(m + n)_ | _O(min(m, n))_ | Easy | EPI | Hash, Binary Search 350| [Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/) | [C++](./C++/intersection-of-two-arrays-ii.cpp) [Python](./Python/intersection-of-two-arrays-ii.py) | _O(m + n)_ | _O(1)_ | Easy | EPI | Hash, Binary Search 360| [Sort Transformed Array](https://leetcode.com/problems/sort-transformed-array/) | [C++](./C++/sort-transformed-array.cpp) [Python](./Python/sort-transformed-array.py) | _O(n)_ | _O(1)_ | Medium |馃摉| 457| [Circular Array Loop](https://leetcode.com/problems/circular-array-loop/) | [C++](./C++/circular-array-loop.cpp) [Python](./Python/circular-array-loop.py) | _O(n)_ | _O(1)_ | Medium || ## Recursion | # | Title | Solution | Time | Space | Difficulty | Tag | Note| |-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----| 95| [Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii/) | [C++](./C++/unique-binary-search-trees-ii.cpp) [Python](./Python/unique-binary-search-trees-ii.py) | _O(4^n / n^(3/2)_ | _O(4^n / n^(3/2)_ | Medium || 98| [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)|[C++](./C++/validate-binary-search-tree.cpp) [Python](./Python/validate-binary-search-tree.py)| _O(n)_ | _O(1)_ | Medium || 100| [Same Tree](https://leetcode.com/problems/same-tree/) |[C+](./C++/same-tree.cpp) [Python](./Python/same-tree.py) | _O(n)_ | _O(h)_ | Easy || 104| [Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/)| [C++](./C++/maximum-depth-of-binary-tree.cpp) [Python](./Python/maximum-depth-of-binary-tree.py)| _O(n)_ | _O(h)_ | Easy || 105| [Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) | [C++](./C++/construct-binary-tree-from-preorder-and-inorder-traversal.cpp) [Python](./Python/construct-binary-tree-from-preorder-and-inorder-traversal.py) | _O(n)_ | _O(n)_ | Medium || 106| [Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/) | [C++](./C++/construct-binary-tree-from-inorder-and-postorder-traversal.cpp) [Python](./Python/construct-binary-tree-from-inorder-and-postorder-traversal.py) | _O(n)_ | _O(n)_ | Medium || 108| [Convert Sorted Array to Binary Search Tree](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/) | [C++](./C++/convert-sorted-array-to-binary-search-tree.cpp) [Python](./Python/convert-sorted-array-to-binary-search-tree.py) | _O(n)_ | _O(logn)_ | Medium || 109| [Convert Sorted List to Binary Search Tree](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/) | [C++](./C++/convert-sorted-list-to-binary-search-tree.cpp) [Python](./Python/convert-sorted-list-to-binary-search-tree.py) | _O(n)_ | _O(logn)_ | Medium || 110| [Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/) | [Python](./Python/balanced-binary-tree.py) | _O(n)_| _O(h)_ | Easy || 111| [Minimum Depth of Binary Tr
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