Gray CodeThe gray code is a binary numeral system where two successive values differ in only one bit.Given a non-negative integer n representing the total number of bits in the code, print the s

Climbing StairsYou are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?Note: Given n

Sqrt(x)Implement int sqrt(int x).Compute and return the square root of x.解题思路：这道题我的思路就是二分法查找结果了，这个比较简单就不多说。public class Solution { public int mySqrt(int x) { long longx = x

Text JustificationGiven an array of words and a length L, format the text such that each line has exactly L characters and is fully (left and right) justified.You should pack your words in a g

Add BinaryGiven two binary strings, return their sum (also a binary string).For example,a = "11"b = "1"Return "100".解题思路：这道题就是两个二进制数相加，记得加上进位的值就好了。public class Solution {

Plus OneGiven a non-negative integer represented as anon-empty array of digits, plus one to the integer.You may assume the integer do not contain any leading zero, except the number 0 itself.

Minimum Path SumGiven a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.Note: You can only move eithe

Unique Paths IIFollow up for "Unique Paths":Now consider if some obstacles are added to the grids. How many unique paths would there be?An obstacle and empty space is marked as 1 and 0 respe

Unique PathsA robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).The robot can only move either down or right at any point in time. The robot is trying

Rotate ListGiven a list, rotate the list to the right by k places, where k is non-negative.For example:Given 1->2->3->4->5->NULL and k = 2,return 4->5->1->2->3->NULL.解题思路：这个题我觉得要分成两种

Palindrome NumberDetermine whether an integer is a palindrome. Do this without extra space.Some hints:Could negative integers be palindromes? (ie, -1)If you are thinking of converting the in

Group AnagramsGiven an array of strings, group anagrams together.For example, given: ["eat", "tea", "tan", "ate", "nat", "bat"],Return:[ ["ate", "eat","tea"], ["nat","tan"], ["bat"]

Rotate Image You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).Follow up:Could you do this in-place?解题思路：题意要求说用原有的空间。所以主要是搞懂那个旋转的顺序就好了

Reverse IntegerReverse digits of an integer.Example1: x = 123, return 321Example2: x = -123, return -321Note:The input is assumed to be a 32-bit signed integer. Your function should retu

Jump Game IIGiven an array of non-negative integers, you are initially positioned at the first index of the array.Each element in the array represents your maximum jump length at that position.

Set Matrix ZeroesGiven a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.click to show follow up.Follow up:Did you use extra space?A straight forward s

Permutation SequenceThe 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

Largest Rectangle in HistogramGiven n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram.Abov

Word SearchGiven a 2D board 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

SubsetsGiven a set of distinct integers, nums, return all possible subsets.Note: The solution set must not contain duplicate subsets.For example,If nums = [1,2,3], a solution is:[ [3],

CombinationsGiven two integers n and k, return all possible combinations of k numbers out of 1 ... n.For example,If n = 4 and k = 2, a solution is:[ [2,4], [3,4], [2,3], [1,2], [1,

Remove Duplicates from Sorted Array IIFollow up for "Remove Duplicates":What if duplicates are allowed at most twice?For example,Given sorted array nums = [1,1,1,2,2,3],Your function s

Partition ListGiven a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.You should preserve the original relative order of the

Merge Sorted ArrayGiven two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.Note:You may assume that nums1 has enough space (size that is greater or equal to

Sort ColorsGiven an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.Here, we will use

Search a 2D MatrixWrite an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:Integers in each row are sorted from left to right.The fir

Pow(x, n) Implement pow(x, n).解题思路：一开始的想法就是简单的一个一个乘...果断TLE了。后面想了以下，应该得用递归的方式，每次都是平方这样来乘，计算复杂度也会降到log2(n)。然后又有一个问题就是n取 -2^32次方的时候，不能直接用n = -n。所以我用一个index来存储n的符号，这样在下一次递归，n = n/2的时候乘以index就

N-QueensThe n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.Given an integer n, return all distinct solutions to the n-queens

Maximum SubarrayFind the contiguous subarray within an array (containing at least one number) which has the largest sum.For example, given the array [-2,1,-3,4,-1,2,1,-5,4],the contiguous

Jump GameGiven an array of non-negative integers, you are initially positioned at the first index of the array.Each element in the array represents your maximum jump length at that position.

Spiral MatrixGiven a matrix of m x n elements (m rows,n columns), return all elements of the matrix in spiral order.For example,Given the following matrix:[ [ 1, 2, 3 ], [ 4, 5, 6 ],

Multiply StringsGiven two non-negative integers num1 andnum2 represented as strings, return the product of num1 andnum2.Note:The length of both num1 and num2 is Both num1 and num2 cont

Trapping Rain WaterGiven 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

Valid ParenthesesGiven a string containing just the characters'(',')', '{', '}', '[' and']', determine if the input string is valid.The brackets must close in the correct order,"()" and"()[]

Remove Nth Node From End of ListGiven a linked list, remove the nth node from the end of list and return its head.For example, Given linked list: 1->2->3->4->5, and n = 2. After removing

Letter Combinations of a Phone NumberGiven a digit string, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone butto

3Sum ClosestGiven an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input wo

3sumGiven 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 set must not con

Longest Common PrefixWrite a function to find the longest common prefix string amongst an array of strings.解题思路：大概就是先拿第一个作为前缀去匹配第二个，更新前缀，不断循环下去直到结束。有一个点就是，可以先比较前缀跟要匹配的String的长度大小，如果前缀长度大于要

Container With Most WaterGiven n non-negative integers a1, a2, ..., an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at