Solution Review: Find Symmetric Pairs in an Array

using System;
using System.Collections.Generic;
namespace chapter_9
{
    class challenge_3
    {
        // Function to find symmetric pairs
        static string findSymmetric(int [,]arr, int size)
        {
            // Create an empty hash table 
            HashSet<string> hash = new HashSet<string>(); ;
            string result = " ";
            // Traverse rows of given 2D array
            for (int i = 0; i < size; i++)
            {
                // Store values in current row
                string pair = "{" + (arr[i,0]).ToString() + ", " +
                  arr[i,1].ToString() + "}";
                // Store values in current row in reverse order
                string reverse = "{" + arr[i,1].ToString() + ", " +
                  arr[i,0].ToString() + "}";
                // Check if reverse pair of current pair is already present in the hash table
                if (hash.Contains(reverse))
                {
                    //Symmetric pair found
                    result += reverse + pair ;
                }
                // Insert pair in hash table
                hash.Add(pair);
            }
            return result;
        }
        static void Main(string[] args)
        {
            int [,] arr = {{1,2},{3,4},{5,9},{4,3},{9,5}};
            string symmetric = findSymmetric(arr, 5);
            Console.WriteLine(symmetric);
            return;
        }
    }
}