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Given 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 the integers 0, 1,

Write 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 first integer of each row is

Given 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 solution using O(mn) space

Given an absolute path for a file (Unix-style), simplify it.For example, path = “/home/”, => “/home” path = “/a/./b/../../c/”, => “/c” click to show corner cases.Corner Cases: Did you consider the

Implement int sqrt(int x).Compute and return the square root of x.我采用的是二分法。每次折中求平方，如果大了就把中值赋给大的，如果小了就把中值赋给小的。public int mySqrt(int x) { long start = 1, end = x; while (start + 1 < end)

Given 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 either down or right at any

Follow 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 respectively in the grid.For ex

A 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 to reach the botto

Given 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.我是利用双指针吧，就可以在一次遍历的情况下找到要断开的位置即倒数第几个位置，然后插到头上

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."123"2."132"3."213"4."231"5

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.For example, Given n = 3,You should return the following matrix:[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5

Given 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.Determine if you are

Given 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 ], [ 7, 8, 9 ]]You should

Find 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 subarray [4,-1,2,1] has the

Implement pow(x, n).其实这个题递归和非递归应该都不难实现，就是边界值的问题。public double myPow(double x, int n) { if (n == 0) return 1.0; double res = 1.0; if (n < 0) { if (x >= 1.

Given an array of strings, group anagrams together.For example, given: [“eat”, “tea”, “tan”, “ate”, “nat”, “bat”], Return:[ ["ate", "eat","tea"], ["nat","tan"], ["bat"]]Note: All inputs will

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?本地使得二维矩阵，旋转90角度。通过实际数据分析，通过两个步骤的元素交换可实现目标：按照主对角线，将对称元素交换 按照列，将对

Given a collection of numbers that might contain duplicates, return all possible unique permutations.For example, [1,1,2] have the following unique permutations:[ [1,1,2], [1,2,1], [2,1,1]][Le

Given a collection of distinct numbers, return all possible permutations.For example, [1,2,3] have the following permutations:[ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1]][Leet

Given two numbers represented as strings, return multiplication of the numbers as a string.Note: The numbers can be arbitrarily large and are non-negative. Converting the input string to integer is N

Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.Each number in C may only be used once in the combination.No

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.The same repeated number may be chosen from C unlimited number of t

Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.You may assume no duplicates in the array.Here

Given a sorted array of integers, find the starting and ending position of a given target value.Your algorithm’s runtime complexity must be in the order of O(log n).If the target is not found in the ar

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 the lowest possible orde

Divide two integers without using multiplication, division and mod operator.If it is overflow, return MAX_INT.以前我记得做过乘法变加法吧，这个有点像除法变减法，用位运算，二进制嘛，左移一位相当于乘以二。一个有趣的是 Math.abs(-2147483648) 结果还是 -2147483648

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is:[ "((()))", "(()())", "(())()", "()(())", "(

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 unique quadruplets in the array which gives the sum of target.Note: The solution set mu

Given a digit string, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone buttons) is given below.Input:Digit string "23"O

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 set must not contain duplic

[LeetCode]–13. Roman to Integer可以在上面的链接看一下罗马数字的排列规律。然后利用规律，构建数组，把基本的构建数放在数组里面，然后依次判断加进去就行。public class Solution { public String intToRoman(int num) { String[][] roman = { {

Given 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 (i, ai) and (i, 0). Find two lin

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.我用的是中心扩展法 因为回文字符串是以中心轴对称的，

Given two non-negative numbers num1 and num2 represented as string, return the sum of num1 and num2.Note:The length of both num1 and num2 is < 5100. Both num1 and num2 contains only digits 0-9. Both

Write a program that outputs the string representation of numbers from 1 to n.But for multiples of three it should output “Fizz” instead of the number and for the multiples of five output “Buzz”. For n

Given a string which consists of lowercase or uppercase letters, find the length of the longest palindromes that can be built with those letters.This is case sensitive, for example “Aa” is not consider

Given an integer, write an algorithm to convert it to hexadecimal. For negative integer, two’s complement method is used.Note:All letters in hexadecimal (a-f) must be in lowercase. The hexadecimal str

Find the sum of all left leaves in a given binary tree.Example: 3 / \ 9 20 / \ 15 7There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.我们递归

A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).Each LED represents a zero or one, with the least significant bit on the

Find the nth digit of the infinite integer sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, …Note: n is positive and will fit within the range of a 32-bit signed integer (n < 231).Example 1:Input: 3Out