using System;

using System.Collections.Generic;

public class Program

{

    static List<List<int>> CombinationSum(List<int> arr, int sum)

    {

        List<List<int>> ans = new List<List<int>>();

        List<int> temp = new List<int>();

        HashSet<int> hs = new HashSet<int>(arr);

        arr.Clear();

        arr.AddRange(hs);

        arr.Sort();

        //

        FindNumbers(ans, arr, sum, 0, temp);

        return ans;

    }

    static void FindNumbers(List<List<int>> ans, List<int> arr, int sum, int index, List<int> temp)

    {

        if(sum == 0)

        {

            ans.Add(new List<int>(temp));

            return;

        }

        for(int i = index; i < arr.Count; i++)

        {

            if(sum - arr[i]  >= 0)

            {

                temp.Add(arr[i]);

                FindNumbers(ans, arr, sum - arr[i], i, temp);

                temp.Remove(arr[i]);

            }

        }

    }

    public static void Main()

    {

        List<int> arr = new List<int>();

        arr.Add(2);

        arr.Add(4);

        arr.Add(6);

        arr.Add(8);

        int sum = 8;

        List<List<int>> ans = CombinationSum(arr, sum);

        if(ans.Count == 0)

        {

            Console.WriteLine("Empty Result!");

            return;

        }

        for(int i = 0; i < ans.Count; i++)

        {

            Console.Write("( ");

            for(int j = 0; j < ans[i].Count; j++)

            {

                Console.Write(ans[i][j]+ " " ); 

            }

            Console.Write(") ");

        }

    }

}

​