```
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
unordered_map<int,int> m;
for (int i = 0; i < nums.size(); ++i) {
if (m.find(target-nums[i]) != m.end())
return {m[target-nums[i]], i};
m[nums[i]] = i;
}
return {};
}
};
```