using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        int[] test1Nums = {2,7,11,15};

        int test1Target = 9;

        PrintArray(TwoSum(test1Nums, test1Target));

        int[] test2Nums = {3,2,4};

        int test2Target = 6;

        PrintArray(TwoSum(test2Nums, test2Target));

        int[] test3Nums = {3,3};

        int test3Target = 6;    

        PrintArray(TwoSum(test3Nums, test3Target));

    }

    public static void PrintArray(int[] array)

    {

         Console.WriteLine("[{0}]", string.Join(", ", array));

    }

    public static int[] TwoSum(int[] nums, int target)

        {

            var numsDictionary = new Dictionary<int, int>();

​

            var complement = 0;

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

            {

                complement = target - nums[i];

                var index = 0;

                if (complement > 0 && numsDictionary.TryGetValue(complement, out index))

                {

                    return new int[] { index, i };

                }

​

                if (numsDictionary.ContainsKey(nums[i]) == false)

                {

                    numsDictionary.Add(nums[i], i);

                }

        }

​

        return null;

    }

}