using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        int[] arr = { 3, 4, 7, 1, 12, 9 };

        FindEqualSums(arr);

    }

    public static void FindEqualSums(int[] arr)

    {

       Dictionary<int, int[]> kvps = new Dictionary<int, int[]>();

       string result = "";

       int sum;

       int[] pair = null;

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

       {

           for(int j = i + 1; j < arr.Length; ++j)

           {

               sum = arr[i] + arr[j];

               if (!kvps.ContainsKey(sum))

               {

                   int[] tArr = new int[2];

                   tArr[0] = arr[i];

                   tArr[1] = arr[j];

                   kvps[sum] = tArr;

               }

               else

               {

                   //sum exists

                   pair = kvps[sum];

                  result += "{" + pair[0].ToString() + "," + pair[1].ToString() + "}{" + arr[i].ToString() + "," + arr[j].ToString() + "}";

                  Console.WriteLine(result);

                  return;

               }

           }

       }

    }

}