两数之和

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int, int> heap;
        for (int i = 0; i < nums.size(); i++) {
            int r = target - nums[i];
            if (heap.count(r))
                return {heap[r], i};
            heap[nums[i]] = i;
        }
        return {};
    }
};