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easy程度题 The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N

medium程度题 题目: Given an input string, reverse the string word by word. For example, Given s = "the sky is blue", return "blue is sky the". 难度在于给定字符串中空格连续出现的次数不限定 如Given s = "   I   lov

medium题 题目: Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand. (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2). You are given a target value

hard程度题 题目: There are two sorted arrays nums1 and nums2 of size m and n respectively. Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Exam

hard程度题 题目: 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 elements se

Hard程度题 题目: Given a linked list, reverse the nodes of a linked list k at a time and return its modified list. k is a positive integer and is less than or equal to the length of the linked lis

easy程度题 题目： Given a linked list, determine if it has a cycle in it. Follow up: Can you solve it without using extra space? 可以建立一个set集合，每次访问一个新节点，如果集合中没有则将节点放入set, 如果有则说明存在环。不占用额外空间，想不出来

medium程度题 题目: Given a singly linked list L: L0→L1→…→Ln-1→Ln, reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→… You must do this in-place without altering the nodes' values. For example, Given {1,2,

easy程度题 题目: Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example, "A man, a plan, a canal: Panama" is a palindrome. "rac

easy程度题 题目： Implement strStr(). Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. 字符串匹配，暴力匹配复杂度O(M * N) AC解: class Solution { public

medium程度题 题目: Implement atoi to convert a string to an integer. Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are t

题目： 思路： 以k为根节点的树，左子树为【1，…，K - 1】，右子树为【K + 1，…，N】，定义f(n)为【1，…，n】能产生不同的二叉搜索树的个数，则以K为根节点能产生f(k - 1) * f(n - k)种不同的树。显然f(0) = f(1) = 1。 f(2) = f(0) * f(1) + f(1) * f(0) f(3) = f(0) * f(2) + f(1) * f(1)

Morris二叉树遍历算法 时间复杂度O（N），空间复杂度O（1） 这种方法借鉴了线索化二叉树的思想，但是不占用空间中序遍历方法如下： 如果当前节点的左孩子为空，则输出当前节点并将其右孩子作为当前节点。 如果当前节点的左孩子不为空，在当前节点的左子树中找到当前节点在中序遍历下的前驱节点。a) 如果前驱节点的右孩子为空，将它的右孩子设置为当前节点。当前节点更新为当前节点的左孩子。b) 如果前驱节点

easy程度题Q:Given two binary trees, write a function to check if they are equal or not.Two binary trees are considered equal if they are structurally identical and the nodes have the same value. 判断两个二叉树是否

Q:Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree [1,2,2,3,4,4,3] is symmetric:1 / \ 2 2 / \ / \ 3 4 4 3But the

Compare two version numbers version1 and version2. If version1 > version2 return 1, if version1 < version2 return -1, otherwise return 0.

easy题 题目： Reverse bits of a given 32 bits unsigned integer. For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in bin

1.题目 Given a string s and a non-empty string p, find all the start indices of p's anagrams in s. Strings consists of lowercase English letters only and the length of both strings s and p will not

从已排好序的数组中去除重复的

Given a non-empty array of integers, return the third maximum number in this array. If it does not exist, return the maximum number. The time complexity must be in O(n). Example 1: Input: [3, 2,

先说第一种题 题目: Given an array of integers, every element appears twice except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it

medium程度题 题目: There are N gas stations along a circular route, where the amount of gas at station i is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel

medium程度 题目： Reverse a linked list from position m to n. Do it in-place and in one-pass. For example: Given 1->2->3->4->5->NULL, m = 2 and n = 4, return 1->4->3->2->5->NULL. Note: Giv

题目: Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules. The Sudoku board could be partially filled, where empty cells are filled with the character '.'. A partia

Easy程度题: 题目: Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input would have exactly one solution, and you

medium程度题 题目: Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. Note: The solution

medium程度题 题目: Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers. If such arrangement is not possible, it must rearrange it as

medium程度题 题目: The set [1,2,3,…,n] contains a total of n! unique permutations. By listing and labeling all of the permutations in order, We get the following sequence (ie, for n = 3): "1

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. For example,  Given [0,1,0,2,1,0,1,3,2,1,2,1]

Reverse digits of an integer. Example1: x = 123, return 321 Example2: x = -123, return -321 click to show spoilers. Have you thought about this? Here are some good questions to ask before c

判断一个整数是否是回文数

题目： 难度： hard思路： O（n）复杂度下感觉要用哈希表，使用两个指针，指向进行的首尾，当发现有包含T字符串的序列时，移动首指针，缩小氛围，大体思路是这样，但是具体细节和代码实现写不出来-，-。 再读懂了其他解答的情况下实现了代码AC解：class Solution { public: string minWindow(string s, string t) { //