using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("GetTargetSum: [1,2,3,9] sum = 8: " + String.Join(",", GetTargetSum(new int[4] { 1,2,3,9 }, 8)));

        Console.WriteLine("GetTargetSum: [1,2,4,4] sum = 9: " + String.Join(",", GetTargetSum(new int[4] { 1,2,4,4 }, 9)));

    }

    public static int[] GetTargetSum(int[] nums, int sum)

    {

        Dictionary<int, int> complements = new Dictionary<int, int>();

        int[] result = new int[2];

        for (int i = 0; i < nums.Length; i++)

        {

            int currentComplement = sum - nums[i];

            if (complements.ContainsKey(nums[i]))

            {

                result[0] = nums[complements[nums[i]]];

                result[1] = nums[i];

                break;

            }

            else if (complements.ContainsKey(currentComplement))

            {

                complements.Add(currentComplement, i);

            }

        }

        return result;

    }

}