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Given an array of integers, find two numbers such that they add up to a specific target number.The function twoSum should return indices of the two numbers such that they add up to the target, where

Reverse digits of an integer.Example1: x = 123, return 321Example2: x = -123, return -321click to show spoilers.Tags: Math【思路】唯一需要注意的是正负号和边界（MAX_VALUE和MIN_VALUE）的判断【上码】public cla

这个题目leetcode上提示用动态规划，但是那样要O(n^2)。我自己想出了一个O(n)的算法，并提交通过。【题目】Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.For "((

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 NA P L S I I

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 the possible input case

我看了几个人气比较高的博客，他们这个算法都没做到O(n^2)，所以提前将我的解法贴出来分享，供大家参考（前面略过的题目近期都会补上的）。【题目】：Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all uniqu

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a link

【分析】该问题的最优解可以从局部的最优解导出，且计算过程中存在大量重复计算，显然是要用动态规划了。用二维布尔数组mem[][]记录每个子串是否为回文，mem[i][j]表示第i个字符到第j个字符间的子串是否为回文。初始化：当i>=j时mem[i][j] =true, i=j时就一个字符必定为回文，ii+1的情况一样处理。过程：若S[i] == S[j]则mem[i][j] = me

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)).Tags: Divide and Conquer, A

前段时间做了一些leetcode。现在有个想法：用java做leetcode并坚持下去。于是开此专题，以便记录、分享和讨论。