using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        List<int> numbers = new List<int>(){1,2,3,4,5};

        List<int> possibleCombination = GetCombination(numbers, new List<int>(), 0);

        Console.Write(string.Join(", ", possibleCombination.Distinct().OrderBy(itm => itm)));

    }

    static List<int> GetCombination(List<int> list, List<int> combinations, int sumNum, bool addNumberToResult = false)

    {

        if (list.Count == 0) {

            return combinations;

        }

        int tmp;

        for (int i = 0; i <= list.Count - 1; i++) {

            tmp = sumNum + list[i];

            if(addNumberToResult){

                combinations.Add(tmp);

            }

            List<int> tmp_list = new List<int>(list);

            tmp_list.RemoveAt(i);

            GetCombination(tmp_list,combinations,tmp, true);

        }

        return combinations;

    }

}