Sum of two numbers

subject ： Given an array of integers nums And an integer target value target, Please find... In the array And is the target value target the Two Integers , And return their array subscripts .

You can assume that each input corresponds to only one answer . however , The same element in the array cannot be repeated in the answer .

You can return the answers in any order .

Test cases ：
Input ：nums = [2,7,11,15], target = 9
Output ：[0,1]
explain ： because nums[0] + nums[1] == 9 , return [0, 1] .

class Solution {
    
public:
    vector<int> twoSum(vector<int>& nums, int target) {
    
      std::unordered_map <int,int> map;
        for(int i = 0; i < nums.size(); i++) {
    
            auto iter = map.find(target - nums[i]);
            if(iter != map.end()) {
    
                return {
    iter->second, i};
            }
            map.insert(pair<int, int>(nums[i], i));
        }
        return {
    };
    }
};