/*

//

// The implementation as below is bit tricky. but not difficult to understand

//

// 1) Traverse the array one by one

// 2) just put the `target - num[i]`(not `num[i]`) into the map

// so, when we checking the next num[i], if we found it is exisited in the map.

// which means we found the second one.

//

vector<int> twoSum(vector<int> &numbers, int target) {

unordered_map<int, int> m;

vector<int> result;

for(int i=0; i<numbers.size(); i++){

// not found the second one

if (m.find(numbers[i])==m.end() ) {

// store the first one poisition into the second one's key

m[target - numbers[i]] = i;

}else {

// found the second one

result.push_back(m[numbers[i]]+1);

result.push_back(i+1);

break;

}

}

return result;

}