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原创 Exact 4SAT问题是NP完全的证明

课后习题8.8，证明4SAT是NP完全的总体思路是将3SAT问题归约到4SAT问题，这样就可以证明EXACT 4SAT是NP完全的。对于一个3SAT问题实例中的子句，可以通过如下方式转换为EXACT 4SAT如果存在重复的文字，我们可以只保留其中一个，如x∨y∨y∨y x \vee y \vee y \vee y变为x∨y x \vee y如果子句中同时存在xx和¬x\lnot x这两种

2017-07-04 23:46:58 460

原创 Leetcode题解 - 337. House Robber III

The thief has found himself a new place for his thievery again. There is only one entrance to this area, called the “root.” Besides the root, each house has one and only one parent house. After a tour,

2017-07-04 22:40:58 195

原创 Leetcode题解 - 565. Array Nesting

A zero-indexed array A consisting of N different integers is given. The array contains all integers in the range [0, N - 1]. Sets S[K] for 0 <= K < N are defined as follows: S[K] = { A[K], A[

2017-07-04 22:12:17 245

原创 Leetcode题解 - 3. Longest Substring Without Repeating Characters

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 answer is “b”, with the le

2017-07-04 22:00:55 195

原创 Leetcode题解 - 452. Minimum Number of Arrows to Burst Balloons

There are a number of spherical balloons spread in two-dimensional space. For each balloon, provided input is the start and end coordinates of the horizontal diameter. Since it’s horizontal, y-coordina

2017-07-04 21:03:54 164

原创 Leetcode题解 - 322. Coin Change

You are given coins of different denominations and a total amount of money amount. Write a function to compute the fewest number of coins that you need to make up that amount. If that amount of money c

2017-07-04 20:09:07 212

原创 Leetcode题解 - 200. Number of Islands

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. You may assume

2017-06-16 14:38:21 253

原创 Leetcode题解 - 61. Rotate List

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. 链接先遍历一次链表找到链表长度，根据要

2017-06-04 21:43:53 160

原创 Leetcode题解 - 20. Valid Parentheses

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 valid

2017-06-04 21:39:13 189

原创 Leetcode题解 - 150. Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation. Valid operators are +, -, *, /. Each operand may be an integer or another expression. Some examples: [“2”,

2017-05-22 11:13:45 270

原创 Leetcode题解 - 554. Brick Wall

here is a brick wall in front of you. The wall is rectangular and has several rows of bricks. The bricks have the same height but different width. You want to draw a vertical line from the top to the b

2017-05-15 11:27:28 377

原创 Leetcode题解 - 14. Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings. 链接给定的字符串存在一个数组中，将第一个字符串作为参考，把后续的字符串依次与strs[0]进行比较即可，双重循环即可完成。class Solution {public:string longestCommonPrefix(

2017-05-08 10:20:02 185

原创 Leetcode题解 - 151. Reverse Words in a String

Given an input string, reverse the string word by word. For example, Given s = “the sky is blue”, return “blue is sky the”. Update (2015-02-12): For C programmers: Try to solve it in-pla

2017-05-03 10:19:33 268

原创 Leetcode题解 - 22. Generate Parentheses

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: [ “((()))”, “(()())”,

2017-04-21 14:09:53 256

原创 Leetcode题解 - 89. Gray Code

The 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 sequence of g

2017-04-14 15:32:21 292

转载 Leetcode题解 - 4. Median of Two Sorted Arrays

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)). Example 1: nu

2017-04-10 11:33:29 282

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

2017-03-31 15:11:53 241

原创 Leetcode题解 - 445. Add Two Numbers II

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it

2017-03-31 15:02:47 233

原创 Leetcode题解 - 208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods. Note: You may assume that all inputs are consist of lowercase letters a-z. 戳我Trie即字典树或者前缀树，如给出字符串”abc”,”ab”,”bd”,”dda”，根据该字符串序列构建一棵

2017-03-31 14:32:41 278

原创 Leetcode题解 - 387. First Unique Character in a String

Given a string, find the first non-repeating character in it and return it’s index. If it doesn’t exist, return -1. Examples: s = “leetcode” return 0. s = “loveleetcode”, return 2.

2017-03-24 14:02:56 190

原创 Leetcode题解 - 56. Merge Intervals

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]. 链接把交叉的区间进行合并，比较简单的方法就是先把给定的区间按照左边元素的大小进行排序，然后两两相邻

2017-03-24 13:48:00 415

原创 Leetcode题解 - 495. Teemo Attacking

In LLP world, there is a hero called Teemo and his attacking can make his enemy Ashe be in poisoned condition. Now, given the Teemo’s attacking ascending time series towards Ashe and the poisoning time

2017-03-24 13:42:23 465

原创 Leetcode题解 - 139. Word Break

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words. You may assum

2017-03-21 17:44:22 269

原创 Leetcode题解 - 215. Kth Largest Element in an Array

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, return 5

2017-03-11 20:31:56 229

原创 Leetcode题解 - 53. Maximum Subarray

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]

2017-03-07 12:50:01 262

原创 Leetcode题解 - 461. Hamming Distance

描述见链接其实本质上很简单就是一个位运算的题目，将两个数按位异或之后统计二进制结果中的数字1的个数就行，代码如下:class Solution {public: int hammingDistance(int x, int y) { int z=x^y; int count=0; while((z!=0)){ if(z%2==1)

2017-02-25 17:55:42 177

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