using System;

using System.Collections.Generic;

public class Program

{

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

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

​

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

            if (hash.TryGetValue(target - nums[i], out int index)) 

                return new int[]{index, i};

            else 

                hash.TryAdd(nums[i], i);

​

        return Array.Empty<int>();

    }

    public static void Main()

    {

        int[] numbers = new int[] {1,1,1,1,1,4,1,1,1,1,1,7,1,1,1,1,1};

        int[] result = TwoSum(numbers, 11);

        Console.WriteLine(string.Join(", ", result));

    }

}