using System;

using System.Linq;

using System.Collections.Generic;

/**

"Given an array of numbers. Print all the pairs (2) of numbers in the array if the sum of those numbers is also present in the array. 

​

Input

int a[] = {10, 5, 2, 7, 7, 49}

Output  (5,2)

​

**/

public class Program

{

    public static void Main()

    {

        var n = new int[] { 1, 2, 3, 4, 15, 8, 7 };

        var tuplePairs = n.Zip(n.Skip(1).Concat(new[] { 0 }), Tuple.Create).SkipLast(1).Where(x => n.Contains(x.Item1+x.Item2));

        foreach(var pairs in tuplePairs)

        {

           Console.WriteLine($"({pairs.Item1},{pairs.Item2}).");

        }

    }

}

​