#include <iostream>
#include <vector>
#include <unordered_map>
using namespace std;

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

int main() {
 
 Solution s;
 vector<int> nums = {2, 7, 11, 15};
 int target = 9;
 vector<int> res = s.twoSum(nums, target);
 for (int i = 0; i < res.size(); i++) {
 cout << res[i] << " ";
 }
 
 return 0;
}