using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static int[][] PairFunction(int [] inputArray, int targetNumber)

    {

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

        var results2 = new Dictionary<int, int>();

        int count = 0;

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

            {

                if (indexDic.ContainsKey(targetNumber - inputArray[i]))

                {

                    results2.Add(inputArray[indexDic[targetNumber - inputArray[i]]] ,inputArray[i]);

                    count++;

                }

                indexDic.Add(inputArray[i], i);

            }

            int[][]results = new int[count][];

            for (int j = 0; j < results2.Count; j++)

            {

                 results[j] = new int[2] { results2.ElementAt(j).Key , results2.ElementAt(j).Value };

            }

        return results;

    }

    public static void Main()

    {

        int[] A = { 1,2,3,4,5,7 };

        int sum = 5;

        int[][] pairArray =  PairFunction(A, sum);

        string[] stringOuput = pairArray.Select(n => "[" + String.Join(",", n) + "]").ToArray();

        Console.WriteLine(String.Join(",", stringOuput));   

    }

}