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原创 [leetcode] Combination Sum IV

思路：记忆化搜索，定义函数查找以index开始，值为target的个数，顺便对nums排序减少不必要的搜索。代码如下：class Solution {public: int combinationSum4(vector& nums, int target) { int result = 0; if(nums.empty() || target ==

2016-07-26 01:34:19 399

原创 [leetcode] Single Number III

同Single Number，异或后按照得到的结果中bit位为1的将数组分为两组，结果必然各存在于这两组中，分别异或得到结果。代码如下：vector singleNumber(vector& nums) { int tmp = 0; vector result(2, 0); for(auto num : nums) { t

2016-03-21 15:01:48 298

原创 [leetcode] Word Pattern

注意一一对应即可：class Solution {public: bool wordPattern(string pattern, string str) { int i = -1, pos = 0; unordered_map mp; unordered_set st; while(++i < pattern.leng

2016-03-19 00:15:05 358

原创 [leetcode] Self Crossing

class Solution {public: bool isSelfCrossing(vector& x) { /*solution 1: only in three cases when cross /* i-2 case 1 : i-1┌─┐ └─┼─

2016-03-18 15:13:38 300

原创 [leetcode] Invert Binary Tree

和最近比较火的一条Twitter相关，题目本身其实并不难...递归和非递归代码如下：/*if(!root) return root; TreeNode* lf = root->left; root->left = invertTree(root->right); root->right = invertTree(lf);

2015-06-14 15:18:48 396

原创 [leetcode] Maximal Square

动态规划，dp[i][j]代表以i,j为右下角的正方形的最长边长。代码如下：int maximalSquare(vector>& matrix) { int result = 0; if(matrix.empty()) return result; const int n = matrix.size();

2015-06-03 16:40:36 1182

原创 [leetcode] Combination Sum III

简单题，和前面两个类似。代码如下：class Solution {public: vector> combinationSum3(int k, int n) { vector > result; vector num; dfs(k, n, result, num, 1); return result; }pri

2015-06-03 15:49:24 1101

原创 [leetcode] House Robber II

和I类似，II变成了环形，即首尾只能取一个。调用两次即可。代码如下：int rob(vector& nums) { if(nums.empty()) return 0; if(nums.size() == 1) return nums[0]; int val = *prev(nums.end());

2015-05-23 18:40:53 308

原创 [leetcode] Add and Search Word - Data structure design

字典树，代码如下：class TrieNode {public: // Initialize your data structure here. TrieNode() { for(int i = 0; i < 26; ++i) next[i] = NULL; end = false; } void ins

2015-05-23 17:46:31 424

原创 [leetcode] Word Search

dfs，代码如下：class Solution {public: bool exist(vector > &board, string word) { const int row = board.size(); const int column = board[0].size(); vector > visited(row, vecto

2015-05-23 17:28:29 351

原创 [leetcode] Word Search II

直接用word search暴力果断超时，根据提示可对words先构建字典树，然后dfs。代码如下：class TrieNode {public: // Initialize your data structure here. TrieNode() { for(int i = 0; i < 26; ++i) next[i] = NULL

2015-05-23 17:27:48 780

原创 [leetcode] Course Schedule II

和Course Schedule类似，记录下结果即可。代码如下：vector findOrder(int numCourses, vector>& prerequisites) { vector result; vector into(numCourses, 0); for(int i = 0; i < prerequisites.size();

2015-05-15 14:41:10 289

原创 [leetcode] Implement Trie (Prefix Tree)

实现字典树基本功能，包括查找key和前缀。代码如下：class TrieNode {public: // Initialize your data structure here. TrieNode() { for(int i = 0; i < 26; ++i) next[i] = NULL; end = false;

2015-05-08 13:59:16 268

原创 [leetcode] Reverse Linked List

链表简单题，遍历头插法即可。代码如下：ListNode* reverseList(ListNode* head) { if(!head) return head; ListNode dummy(-1); dummy.next = head; ListNode *cur = head; Lis

2015-05-07 14:56:48 293

原创 [leetcode] Course Schedule

图算法，判断有向图是否存在回路。拓扑排序即可，代码如下：bool canFinish(int numCourses, vector>& prerequisites) { vector into(numCourses, 0); for(int i = 0; i < prerequisites.size(); ++i) into[prereq

2015-05-07 14:52:21 700

原创 [leetcode] Isomorphic Strings

简单题，map记录下即可~代码如下：bool isIsomorphic(string s, string t) { if(s.length() != t.length()) return false; unordered_map mp1; unordered_map mp2; for(int i = 0;

2015-04-30 15:29:48 425

原创 [leetcode] Happy Number

简单题，模拟并记录即可~代码如下：bool isHappy(int n) { unordered_set appear; while(n != 1){ appear.insert(n); int tmp = n; n = 0; while(tmp){

2015-04-22 11:01:31 290

原创 [leetcode] Bitwise AND of Numbers Range

简单题，当m和n不相等时，即区间内必存在奇偶数，故低位AND后取0，故结果为m和n从高位开始取相等的那些位得到的值。代码如下：int rangeBitwiseAnd(int m, int n) { int p = 0; while(m != n && m != 0){ ++p; m >>= 1;

2015-04-20 21:47:14 342

原创 [leetcode] Number of Islands

BFS或DFS，利用grid数组来标记是否访问。代码如下：int numIslands(vector> &grid) { if(grid.empty()) return 0; const int m = grid.size(); const int n = grid[0].size(); int dir[4

2015-04-14 16:56:34 305

原创 [leetcode] Binary Tree Right Side View

dfs，记录已经访问到的层数即可。代码如下：vector rightSideView(TreeNode *root) { vector result; int curLevel = 0, level = -1; dfs(result, curLevel, level, root); return result; }

2015-04-07 22:09:32 371

原创 [leetcode] House Robber

简单题，代码如下：int rob(vector &num) { if(num.empty()) return 0; int pre = 0, cur = num[0]; int result = cur; for(int i = 1; i < num.size(); ++i){ re

2015-04-07 22:07:30 258

原创砝码分块全称重问题

问题描述：一个M重的砝码，最少分成N块，使得所有1-M重的物品都可以用这N块砝码称出。分析：1、很容易想到二进制的方法，即每一块可以取也可以不取，即0和1，分类即1+2+4+...+2^(N-2)+X=M。证明：由二进制可知1-(2^(N-1)-1)都可以称出，设现在需要称出2^(N-1)-1+Y的重量(Y可由前N-1个砝码中去除重量和为X-Y的砝码，加上第N个砝码后重量为

2015-03-03 10:36:01 500

原创 [leetcode] Department Top Three Salaries

简单连接统计~~select d.Name as Department,ee.Name as Emplyee,ee.Salary as Salaryfrom Department d,( select * from Employee e where (select count(distinct Salary) from Employee where

2015-01-26 17:36:54 1162

原创 [leetcode] Consecutive Numbers

用用户变量记录出现次数即可~select distinct NUM from( select NUM, @count := if(@prevNum = NUM, @count + 1, 1) as cnt, @prevNum := NUM from Logs, (select @prevNum := NULL) pn, (select @count := 0) ct o

2015-01-22 16:28:04 1562

原创 [leetcode] Largest Number

bool cmp(const int &a, const int &b){ string sa = to_string(a); string sb = to_string(b); return sa + sb > sb + sa;}class Solution {public: string largestNumber(vector &num) {

2015-01-21 13:11:34 362

原创 [leetcode] Dungeon Game

动态规划，代码如下：int calculateMinimumHP(vector > &dungeon) { const int m = dungeon.size(); const int n = dungeon[0].size(); int dp[m][n]; dp[m - 1][n - 1] = getMin(1 - dun

2015-01-09 15:21:54 633

原创 [leetcode] Fraction to Recurring Decimal

细节题，余数出现相同时即循环节。代码如下：string fractionToDecimal(int numerator, int denominator) { int flag = 1; long long lnum = numerator, lden = denominator; if(numerator < 0){ lnum =

2014-12-19 09:27:04 350

原创 [leetcode] Compare Version Numbers

细节题，代码如下：int compareVersion(string version1, string version2) { int index1 = 0, index2 = 0; while(index1 < version1.length() || index2 < version2.length()){ int temp1, te

2014-12-17 09:56:15 404

原创 [leetcode] Merge Intervals

细节题，代码如下： bool comp(const Interval &a, const Interval &b){ if(a.start == b.start) return a.end < b.end; return a.start < b.start;}class Solution {public: vector me

2014-11-13 13:51:45 306

原创 [leetcode] Insert Interval

细节题，代码如下：

2014-11-13 13:42:46 284

原创最近点对问题

编程之美，最近点对问题（二维）。代码如下：

2014-10-16 14:58:58 421

转载 Pattern Searching using a Trie of all Suffixes

以下是构造banana\0的后缀树：

2014-09-04 16:41:25 361

转载树状数组

树状数组是对一个数组改变某个元素和求和比较实用的数据结构。两中操作都是O(logn)。在解题过程中，我们有时需要维护一个数组的前缀和S[i]=A[1]+A[2]+...+A[i]。但是不难发现，如果我们修改了任意一个A[i],S[i]、S[i+1]...S[n]都会发生变化。可以说，每次修改A[i]后，调整前缀和S[]在最坏情况下会需

2014-07-16 10:55:37 260

原创 [leetcode] Longest Valid Parentheses

用栈，并改变匹配的括号在s中的位置的值为‘0’。最后统计连续0的geshu

2014-07-04 17:34:37 308

原创 [leetcode] Minimum Window Substring

代码如下：class Solution {public: string minWindow(string S, string T) { unordered_map count; unordered_map found; int index = 0, minLen = INT_MAX; int num = 0;

2014-07-04 16:42:25 468