Solution Review: Find Two Pairs in an Array with an Equal Sum

using System;
using System.Collections.Generic;
namespace chapter_9
{
    class challenge_5
    {
        static string findPair(int[] arr, int size)
        {
            string result = "";
            // Create HashMap with Key being sum and value being a pair i.e key = 3 , value = {1,2}
            // Traverse all possible pairs in given arr and store sums in map
            // If sum already exist then print out the two pairs.
            Dictionary<int, int[]> hMap = new Dictionary<int, int[]>();
            int sum;
            int[] prev_pair = null;
            for (int i = 0; i < size; ++i)
            {
                for (int j = i + 1; j < size; ++j)
                {
                    sum = arr[i] + arr[j]; //calculate sum
                    if (!hMap.ContainsKey(sum))
                    {
                        // If the sum is not present in Map then insert it along with pair
                        int[] temp_Arr = new int[2];
                        temp_Arr[0] = arr[i];
                        temp_Arr[1] = arr[j];
                        hMap[sum] = temp_Arr;
                    }
                    else
                    {
                        //Sum already present in Map
                        prev_pair = hMap[sum];
                        // Since array elements are distinct, we don't
                        // need to check if any element is common among pairs
                        result += "{" + prev_pair[0].ToString() + "," + prev_pair[1].ToString() + "}{" + arr[i].ToString() + "," + arr[j].ToString() + "}";
                        return result;
                    }
                }
            }//end of for
            return result;
        }
        static void Main(string[] args)
        {
            int[] arr = { 3, 4, 7, 1, 12, 9 };
            Console.WriteLine(findPair(arr, 6));
        }
    }
}