import java.util.Arrays;
import java.util.HashMap;

class Solution {
    public static void main(String[] args) {
      int[] test1 = {2, 7, 11, 15}; int target1 = 9;
      int[] test2 = {3, 2, 4}; int target2 = 6;
      int[] test3 = {3, 3}; int target3 = 6;


      System.out.println("twoSum( " + Arrays.toString(test1) + ", " + target1 + " ): " + Arrays.toString(twoSum(test1, target1)));
      System.out.println("twoSum( " + Arrays.toString(test2) + ", " + target2 + " ): " + Arrays.toString(twoSum(test2, target2)));
      System.out.println("twoSum( " + Arrays.toString(test3) + ", " + target3 + " ): " + Arrays.toString(twoSum(test3, target3)));

    }

    static int[] twoSum(int[] nums, int target) {
        int[] res = new int[2];

        HashMap<Integer, Integer> d = new HashMap<>();

        for (int i = 0; i < nums.length; i++) {
          var remainderIdx = d.get(target - nums[i]);
          if (remainderIdx != null) {
            res[0] = i;
            res[1] = remainderIdx;
            return res;
          } else {
            d.put(nums[i], i);
          }
        }
        
        return res;
    }
}