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原创算法概论8.15 最大公共子图

题目：证明如下问题是NP-完全的：输入：两个图G1 = （V1，E1），G2 = （V2，E2）；预算b。输出：两个节点集合V1‘⊆V1，V2’⊆V2，将它们移除后，将在两图中分别留下至少b个结点，且图的剩余部分完全相同。解答：我们已知求给定图的最大独立集问题是NP完全问题，由此可以将最大独立集问题归约到此问题。假设给定的G1 = （V，E），G2 =

2017-01-13 21:59:52 2509

原创 376. Wiggle Subsequence 类别：动态规划难度：medium

题目：A sequence of numbers is called a wiggle sequence if the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be e

2017-01-08 22:24:10 297

原创 279. Perfect Squares 类别：medium 难度：medium

题目：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;

2017-01-08 22:21:34 291

原创 64. Minimum Path Sum 类别：动态规划难度：medium

题目：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.思路：转移方程：dp[i][j] = min(grid[m -

2017-01-08 22:19:40 242

原创 416. Partition Equal Subset Sum 类别：动态规划难度：medium

题目：Given a non-empty array containing only positive integers, find if the array can be partitioned into two subsets such that the sum of elements in both subsets is equal.Note:Each of

2017-01-08 22:17:56 840

原创 198. House Robber 类别：动态规划难度：easy

题目：You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjac

2017-01-08 22:15:00 246

原创 70. Climbing Stairs 类别：动态规划难度：easy

题目：You 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?思路：类似斐波那契序列。

2017-01-08 22:12:56 240

原创 62. Unique Paths 类别：动态规划难度：medium

题目：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 r

2017-01-08 22:11:13 251

原创 343. Integer Break 类别：动态规划难度：medium

题目：Given a positive integer n, break it into the sum of at least two positive integers and maximize the product of those integers. Return the maximum product you can get.For example, given n

2017-01-08 22:08:49 311

原创 357. Count Numbers with Unique Digits 类别：动态规划难度：medium

题目：Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x n.Example:Given n = 2, return 91. (The answer should be the total numbers in the range of 0 ≤ x [11,

2017-01-08 22:06:14 245

原创 442. Find All Duplicates in an Array 难度：medium

题目：Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.Find all the elements that appear twice in this array.Could you do it w

2017-01-08 21:34:23 224

原创 463. Island Perimeter 难度：easy

题目：You are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water. Grid cells are connected horizontally/vertically (not diagonally). The grid is co

2017-01-08 21:09:27 193

原创 448. Find All Numbers Disappeared in an Array 难度：easy

题目：Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.Find all the elements of [1, n] inclusive that do not appear in this a

2017-01-08 21:04:03 171

原创 419. Battleships in a Board 难度：medium

题目：Given an 2D board, count how many different battleships are in it. The battleships are represented with 'X's, empty slots are represented with '.'s. You may assume the following rules:Y

2017-01-08 20:58:52 168

原创 461. Hamming Distance 难度：easy

题目：The Hamming distance between two integers is the number of positions at which the corresponding bits are different.Given two integers x and y, calculate the Hamming distance.Note:

2017-01-08 20:53:45 168

原创 118. Pascal's Triangle 难度：easy

题目：Given numRows, generate the first numRows of Pascal's triangle.For example, given numRows = 5,Return[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]思路：每一层的第i个位置，等于

2017-01-07 12:44:24 182

原创 75. Sort Colors 难度：medium

题目：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

2017-01-07 12:41:46 198

原创 66. Plus One 难度：easy

题目：Given a non-negative integer represented as a non-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.

2017-01-07 12:32:09 225

原创 27. Remove Element 难度：easy

题目：Given an array and a value, remove all instances of that value in place and return the new length.Do not allocate extra space for another array, you must do this in place with constant me

2017-01-07 12:01:07 154

原创 367. Valid Perfect Square 难度：medium

题目：Given a positive integer num, write a function which returns True if num is a perfect square else False.Note: Do not use any built-in library function such as sqrt.Example 1:Input:

2017-01-07 11:47:57 176

原创 334. Increasing Triplet Subsequence 难度：medium

题目：Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.Formally the function should:Return true if there exists i, j, k such that

2017-01-07 11:38:07 158

原创 77. Combinations 难度：medium

题目：Given 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], [1,3],

2017-01-07 10:47:16 266

原创 235. Lowest Common Ancestor of a Binary Search Tree 难度：easy

题目：Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.According to the definition of LCA on Wikipedia: “The lowest common ancestor is def

2017-01-06 21:51:10 242

原创 263. Ugly Number 难度：easy

题目：Write a program to check whether a given number is an ugly number.Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not

2017-01-06 21:35:41 206

原创 191. Number of 1 Bits 难度：easy

题目：Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).For example, the 32-bit integer ’11' has binary representati

2017-01-06 21:31:12 192

原创 153. Find Minimum in Rotated Sorted Array

题目：Suppose an array sorted in ascending order 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).Find the minimum element.思路：用二分法

2017-01-06 21:26:24 161

原创 199. Binary Tree Right Side View 难度：medium

题目：Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.For example:Given the following binary tree

2017-01-06 21:17:13 186

原创 202. Happy Number 难度：easy

题目：Write an algorithm to determine if a number is "happy".A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of th

2017-01-06 20:14:12 193

原创 386. Lexicographical Numbers 难度：medium

题目：Given an integer n, return 1 - n in lexicographical order.For example, given 13, return: [1,10,11,12,13,2,3,4,5,6,7,8,9].思路：优先将数字乘10；如果数字末位＜9，考虑将数字加1。程序：class Solution {p

2017-01-06 20:02:20 221

原创 394. Decode String 难度：medium

题目：Given an encoded string, return it's decoded string.The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times. Note

2017-01-04 20:37:02 220

原创 137. Single Number II 难度：medium

题目：Given an array of integers, every element appears three times except for one. Find that single one.思路：那么对这32位中的每一位做相同的处理，也就是说，逐位把所有的输入加起来，并且看看第i位的和除以3的余数，这个余数就是single numer在第i位的取值。这样就

2017-01-04 19:41:13 150

原创 337. House Robber III 难度：medium

题目：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. Aft

2017-01-04 19:30:13 354

原创 230. Kth Smallest Element in a BST 难度：medium

题目：Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.Note: You may assume k is always valid, 1 ≤ k ≤ BST's total elements.思路：

2017-01-01 23:31:00 171

原创 318. Maximum Product of Word Lengths 难度：easy

题目：Given a string array words, find the maximum value of length(word[i]) * length(word[j]) where the two words do not share common letters. You may assume that each word will contain only lowe

2017-01-01 20:57:01 199

原创 447. Number of Boomerangs 难度：easy

题目：Given n points in the plane that are all pairwise distinct, a "boomerang" is a tuple of points (i, j, k) such that the distance between i andj equals the distance between i and k (the o

2017-01-01 20:21:36 156

原创 454. 4Sum II 难度：medium

题目：Given four lists A, B, C, D of integer values, compute how many tuples (i, j, k, l) there are such that A[i] + B[j] + C[k] + D[l] is zero.To make problem a bit easier, all A, B, C, D ha

2017-01-01 20:02:00 210

原创 378. Kth Smallest Element in a Sorted Matrix 难度：medium

题目：Given a n x n matrix where each of the rows and columns are sorted in ascending order, find the kth smallest element in the matrix.Note that it is the kth smallest element in the sorted o

2017-01-01 18:14:28 233

原创 477. Total Hamming Distance 难度：medium

题目：The Hamming distance between two integers is the number of positions at which the corresponding bits are different.Now your job is to find the total Hamming distance between all pairs o

2017-01-01 17:55:42 195

原创 268. Missing Number 难度：medium

题目：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.思路：等差数列求和，再逐个减去数

2016-12-30 22:25:28 168

原创 350. Intersection of Two Arrays II 难度：easy

题目：Given two arrays, write a function to compute their intersection.Example:Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2].Note:Each element in the result should app

2016-12-30 22:19:59 152

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