GigaCat

http://blog.youkuaiyun.com/fightforyourdream/article/details/14449133

http://blog.youkuaiyun.com/yutianzuijin/article/details/16850031

Implement strStr().Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.这道题有很多需要注意的小点：（1）You have to check if a String == null before

最初想到的简单暴力算法，超时了：public class Solution { public int divideHelper(int dividend, int divisor){ int result = 0; if(divisor == 0) return 0; else{ while(true){

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

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.AC代码，虽然有点复杂，但是一次通过了。public class Solution { public void setZeroes(int[][] matrix) {

Given two words (start and end), and a dictionary, find the length of shortest transformation sequence from start to end, such that:Only one letter can be changed at a timeEach intermediat

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."race a car" is not a

Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.)You have the following 3 operations permitted on a word:

Determine 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 integer to string, no

1Two Sum25arraysort    setTwo Pointers2Add Two Numbers34linked listTwo Pointers   

找了很久还是没有找到巧解的方法。下面是暴力算法的博客链接：http://blog.youkuaiyun.com/worldwindjp/article/details/18882849

Given an array of integers, every element appears three times except for one. Find that single one.Note:Your algorithm should have a linear runtime complexity. Could you implement it without usi

Given a binary tree, return the postorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [3,2,1].Note: Recursive solution is t

随笔自用http://oj.leetcode.com/problems/binary-tree-level-order-traversal-ii/

Given 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 the second node from the end, the

Given a set of non-overlapping intervals, insert a new interval into the intervals (merge if necessary).You may assume that the intervals were initially sorted according to their start times.E

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 without using ext

Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n).For example,S = "ADOBECODEBANC"T = "ABC"Minimum window is "BAN

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). Fin

Follow up for N-Queens problem.Now, instead outputting board configurations, return the total number of distinct solutions.本题主要是深度优先搜索：public class Solution { public int totalNQueens

Given a string containing only digits, restore it by returning all possible valid IP address combinations.For example:Given "25525511135",return ["255.255.11.135", "255.255.111.35"]. (Order

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.An example is the root-to-leaf path 1->2->3 which represents the number 123.Find the tota

There are two sorted arrays A and B 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)).我写的太不简洁了，也没有优化，不过AC了：public cla

Suppose a sorted array 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 to search. If found in the array retur

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] ha

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 {1,2,3,4}, reorder it to

Given a set of distinct integers, S, return all possible subsets.Note:Elements in a subset must be in non-descending order.The solution set must not contain duplicate subsets.For exa

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.OJ's undirected graph serialization:Nodes are labeled uniquely.We use # as a separator for ea

利用递归的算法，观察*的位置，这道题非常好。public class Solution { public boolean isMatch(String s, String p) { // Start typing your Java solution below // DO NOT write main() function if(s.l

http://blog.youkuaiyun.com/sbitswc/article/details/20110655

转自： http://blog.youkuaiyun.com/pickless/article/details/9040293选定一个位置，朝两边不断拓展，直到两边的字符不一样为止。这是最简单、最直观的想法，这个想法的时间复杂度是O(n2)。但是这不是最快速的算法，目前对于最长回文子串问题最快的解法的时间复杂度为O(n)。假设S=“gxgag

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 ca

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

Given a 2D board containing 'X' and 'O', capture all regions surrounded by 'X'.A region is captured by flipping all 'O's into 'X's in that surrounded region.For example,X X X XX O O X

Follow up for "Search in Rotated Sorted Array":What if duplicates are allowed?Would this affect the run-time complexity? How and why?Write a function to determine if a given target is in the

Given an array of strings, return all groups of strings that are anagrams.Note: All inputs will be in lower-case.这是我找到的最喜欢的解法。/* The idea is to use a hashmap to collect groups of anagr

Given a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtree of a node contains only nodes with keys less than the node's key.Th

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.首先，展示一个我看到的最吊，碉堡了的算法：import java.math

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