[leetcode]Two Sum
来源:互联网 发布:网店客服知多少ppt 编辑:程序博客网 时间:2024/06/06 21:03
问题描述:
Given an array of integers, find two numbers such that they add up to a specific target number.
The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have exactly one solution.
Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2
基本思路:
O(n2) runtime, O(1) space – Brute force:
The brute force approach is simple. Loop through each element x and find if there is another value that equals to target – x. As finding another value requires looping through the rest of array, its runtime complexity isO(n2).
O(n) runtime, O(n) space – Hash table:
We could reduce the runtime complexity of looking up a value toO(1) using a hash map that maps a value to its index.
代码:
vector<int> twoSum(vector<int> &numbers, int target) { //consider the same num; vector<int> result; map<int,int> num_pos; map<int,int>::iterator iter; for(int i = 0; i < numbers.size(); i++){ int diff = target - numbers[i]; iter = num_pos.find(diff); if(iter != num_pos.end()){ result.push_back(iter->second); result.push_back(i+1); break; } num_pos.insert(make_pair(numbers[i],i+1)); } return result; }
- 【Leetcode】Two Sum (Sum)
- LeetCode: Two Sum
- LeetCode: Two Sum
- [Leetcode] Two Sum
- LeetCode : Two Sum
- Leetcode: Two Sum
- leetcode 46: Two Sum
- [LeetCode] Two Sum
- LeetCode 1 - Two Sum
- Leetcode : Two Sum
- 【leetcode】Two Sum
- [LeetCode]Two Sum
- leetcode Two Sum
- [Leetcode] Two Sum
- [leetcode] Two Sum
- LeetCode - Two Sum
- leetcode之Two Sum
- LeetCode | Two Sum
- 最短路径算法——Dijkstra,Bellman-Ford,Floyd-Warshall,Johnson
- 2015校招经典算法笔试题
- smb
- 【DP】 POJ 1160 Post Office
- 【Axure教程】动态面板制作弹出框效果
- [leetcode]Two Sum
- 【Axure教程】动态面板制作弹出框效果
- JSP中的include指令和include动作
- 面试!!切记!!切记!!
- BZOJ 1861 ZJOI2006 Book 书架 Splay
- C#三层实例——未能找到元数据文件”xxx.dll”(实战篇1)
- input<typr=text>的size属性和maxlength属性
- 如何巧妙、有效地使用Google搜索--Google搜索技巧
- hdu 1698