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原创 Leetcode解题报告：279. Perfect Squares

题意：Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.For example, given n = 12, return 3 because 12 = 4 + 4 + 4; gi

2017-01-07 20:10:25 354

原创算法概论习题：8.14NP-完全问题的证明

8.14问题描述：证明如下问题是NP-完全的：给定一个无向图G（V，E）和整数k，求G的一个规模为K的团以及一个规模为K的独立集，假设二者都是存在的。（1）可以将3SAT问题归约到求无向图G的规模为K的团。考虑一个有K个子句的3SAT实例，每个字句包含不超过3个文字。可以构造一个无向图G，每个属于3SAT公式中的文字对应G中的一个节点。在3SAT公式中属于一个子句的结点在图G

2016-12-24 01:53:07 1335

原创 leetcode解题报告：62. Unique Paths

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

2016-11-27 21:38:48 336

原创 Leetcode解题报告：207. Course Schedule

题目：There are a total of n courses you have to take, labeled from 0 to n - 1.Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expr

2016-11-26 23:47:38 489

原创 leetcode解题报告：392. Is Subsequence

题目：Given a string s and a string t, check if s is subsequence of t.You may assume that there is only lower case English letters in both s and t. t is potentially a very long (length ~= 500,0

2016-11-23 15:48:35 282

原创 leetcode解题报告:53. Maximum Subarray

题意：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]

2016-11-22 00:41:10 302

原创 leetcode解题报告：45. Jump Game II

题意：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.Your

2016-11-14 21:06:11 315

原创 Leetcode解题报告：406. Queue Reconstruction by Height

题意：Suppose you have a random list of people standing in a queue. Each person is described by a pair of integers (h, k), where h is the height of the person and k is the number of people in fro

2016-11-14 19:45:37 467

原创 leetcode解题报告:213. House Robber II

题意：After robbing those houses on that street, the thief has found himself a new place for his thievery so that he will not get too much attention. This time, all houses at this place are arranged

2016-10-31 16:01:20 250

原创 leetcode解题报告：338. Counting Bits

Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1's in their binary representation and return them as an array.Example:For num =

2016-10-22 19:00:23 550

原创 leetcode解题报告：56. Merge Intervals

题意：Given a collection of intervals, merge all overlapping intervals.For example,Given [1,3],[2,6],[8,10],[15,18],return [1,6],[8,10],[15,18].难度：Hard解题思路：需要把有重复区间的所有区间合并成1个，不与其他区间重复

2016-10-10 17:42:41 242

原创 leetcode解题报告：238. Product of Array Except Self

题意：Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements ofnums except nums[i].Solve it without division

2016-10-06 01:58:28 252

原创 leetcode解题报告：75. Sort Colors

题意：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 intege

2016-10-04 23:52:06 278

原创 Leetcode解题报告：94. Binary Tree Inorder Traversal

题意：Given a binary tree, return the inorder traversal of its nodes' values.难度：Medium解题思路：简单的中序遍历问题，当根节点存在左子树的时候，先遍历左子树，当返回到跟结点的时候，把根节点值加入答案数组，再遍历右子树（如果存在的话）。时间复杂度O（n），如果当前结点没有左右子树，当前值也要加入答案数组。/

2016-10-04 00:52:37 293

原创 leetcode解题报告：135. Candy

题意：There are N children standing in a line. Each child is assigned a rating value.You are giving candies to these children subjected to the following requirements:Each child must have at least

2016-10-02 19:10:31 474

原创 Leetcode解题报告：73. Set Matrix Zeroes

题意：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

2016-10-02 15:43:34 308

原创 Leetcode解题报告：48. Rotate Image

题意：You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).难度:Medium解题思路一：顺时针旋转90°，其实就是第i列倒序变成第 i行，很容易想到先把原矩阵复制到一个temp矩阵中，然后再遍历一次，把temp中的列按倒序

2016-10-01 14:46:31 235

原创 leetcode解题报告:104. Maximum Depth of Binary Tree

题意：Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.难度：Easy解题思路：这是一道简单的深

2016-09-28 00:50:15 379

原创 leetcode解题报告：129. Sum Root to Leaf Numbers

题意：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 t

2016-09-25 15:00:58 307

原创 Leetcode解题报告：Search Insert Position

题目大意：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 a

2016-09-21 00:01:51 266

原创 Leetcode解题报告：4. Median of Two Sorted Arrays

题意：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)).难度：Hard解题

2016-09-20 01:48:28 503

原创 Leetcode解题报告：74. Search a 2D Matrix

题目大意：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 inte

2016-09-14 11:45:52 249

原创 Leetcode解题报告：268. Missing Number

题意：Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.For example,Given nums = [0, 1, 3] return 2.Note:Your algori

2016-09-14 11:01:56 303

原创 Leetcode解题报告:215. Kth Largest Element in an Array

题目大意：Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.For example,Given [3,2,1,5,6,4] and k = 2,

2016-09-14 00:24:10 296

原创 leetcode解题报告：240. Search a 2D Matrix II

题目大意：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 in ascending from left to right.I

2016-09-12 19:25:51 533

原创 Leetcode解题报告:169. Majority Element

题意：Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.You may assume that the array is non-empty and the majority e

2016-09-11 00:48:31 210

原创 Leetcode题解：127. Word Ladder

Given two words (beginWord and endWord), and a dictionary's word list, find the length ofshortest transformation sequence from beginWordto endWord, such that:Only one letter can be changed at a

2016-09-07 02:12:44 338

原创 Leetcode题解：55. Jump Game

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 i

2016-09-06 21:58:30 241

原创 leetcode题解：Number of Islands

题号200题意：Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically.

2016-09-06 14:16:43 404

原创 Leetcode题解：First Unique Character in a String

题目：Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.难度：Easy解题思路：比较容易想到的方法是用哈希表，先遍历一遍字符串，因为只有26个小写字母，开一个大小为26的数组a，对每一个扫到的字母，a[s[i]-

2016-09-06 01:17:40 291

原创 Leetcode题解：Longest Substring Without Repeating Characters

问题描述：Given a string, find the length of the longest substring without repeating characters.Examples:Given "abcabcbb", the answer is "abc", which the length is 3.Given "bbbbb", the

2016-09-06 00:57:08 479

原创 Leetcode题解：Pow(x, n)

题目描述：Implement pow(x, n). 难度 Medium解题思路：利用分治法（Divide and Conquer）,对n进行划分，如果n为偶数，那么可以先求出x^(n/2) ,得到结果后对其求平方，即可得到x^n=x^(n/2) * x^(n/2). 如果n为奇数，则x^n=x^((n-1)/2)*x^((n-1)/2)*x. 这样一来一个规

2016-09-05 22:53:25 498

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