题目描述：
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
相信当你看见这篇博客时，已经独立思考过，这里直接给出Accepted Code。部分代码来自网络，希望不会涉及版权问题。
Solution1:
vector<int> twoSum(vector<int> &numbers, int target) { vector<int> res(2); int len = numbers.size(); map<int,int> mp; for(int i = 0;i < len;++i) mp[numbers[i]] = i; map<int,int>::iterator it = mp.end(); int tmp; for(int i = 0;i < len;++i) { tmp = target - numbers[i]; it = mp.find(tmp); if(it != mp.end() && i != it->second) { res[0] = i+1; res[1] = mp[tmp]+1; break; } } return res; }
Solution2:
vector<int> twoSum(vector<int> &numbers, int target) { vector<int> res(2); int len = numbers.size(); map<int,int> mp; map<int,int>::iterator it = mp.end(); int tmp; for(int i = 0;i < len;++i) { tmp = target - numbers[i]; it = mp.find(tmp); if(it != mp.end()) { res[0] = mp[tmp]+1; res[1] = i+1; break; } mp[numbers[i]] = i; } return res; }
两段代码非常相似，仅部分细节不同。如有疑问，欢迎交流。
原文：http://www.cnblogs.com/gattaca/p/4122041.html