two Sum Given an array of integers, return indices of the two numbers such that they add up to a specific targ…

Given a string S and a string T, count the number of distinct subsequences of T in&nb…

7. Reverse Integer 题目简介：翻转一个数字的数字部分的字符，即负数的“-”位置不变，只翻转数字部分。当翻转后的数字溢出时（超过32有符号整数的范围），返回0。 解题思路：将数字转成字符串，利用字符串的翻…

实现一个将字符串进行指定行数的转换的函数: 将字符串 “PAYPALISHIRING” 以Z字形排列成给定的行数：（下面这样的形状） 之后按逐行顺序依次排列：”PAHNAPLSIIGYIR” P A H N A P L …

Given a string s and a dictionary of words dict, determine if s can be segmented into…

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of…

**题目：**Merge Two Sorted Lists Merge two sorted linked lists and return it as a new list. The new list should b…

**题目：**Valid Parentheses Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determ…

一. 题目描述 Given a string which contains only lowercase letters, remove duplicate letters so that every letter ap…

一. 题目描述 The thief has found himself a new place for his thievery again. There is only one entrance to this are…

题目： Merge two sorted linked lists and return it as a new list. The new list should be made by splicing togethe…

最长有效括号 1. 题目描述： 给定一个只包含 '(' 和 ')' 的字符串，找出最长的包含有效括号的子串的长度。 示例1： 输入: "(()" 输出: 2 解释: 最长有效括号子串为 "()" 示例…