using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

public class Program
{
    static void Main()
    {
       var result =  Combinations(new List<string> { "1", "2", "3", "4", "5" }, 5);

       foreach (var combination in result)
       {
           Console.WriteLine(combination);
       }
    }

    static IEnumerable<string> Combinations(List<string> characters, int length)
    {
        for (int i = 0; i < characters.Count; i++)
        {
            // ако листът има 1 елемент, алгоритъмът го връща
            if (length == 1)
                yield return characters[i];
            // генерира всички комбинации, без повторения
            else
                foreach (string next in Combinations(characters.GetRange(i + 1, characters.Count - (i + 1)), length - 1))
                {
                    yield return characters[i] + next;
                }
        }
    }
}