text: class Solution {
  public:
    vector<int> twoSum(vector<int> &nums, int target) {
      // number -> index in array
      unordered_map<int, int> numberMap; // hash table in c++
  
      for (int i = 0; i < nums.size(); i++) {
        if (numberMap.count(target - nums[i])) {
          return {numberMap[target - nums[i]], i};
        }
        numberMap[nums[i]] = i;
      }
  
      return {};
    }
  };
  