1. 题目

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

Example:

Because nums[0] + nums[1] = 2 + 7 = 9,

2. 思路

建立hashmap，去查找余数是否存在。

3. 代码

class Solution {public:    vector
    
      twoSum(vector
     
      & nums, int target) {        vector
      
        res;        _map.clear();        int size = nums.size();        for (int i = 0; i < size; i++) {            int cur = nums[i];            int need = target - cur;            auto f = _map.find(need);            if (f != _map.end()) {                                res.push_back(f->second + 1);                res.push_back(i + 1);                return res;            }            _map[cur] = i;        }        return res;    }private:    unordered_map
       
         _map;};