using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        int res = CountNumbersWithUniqueDigits(3);

        Console.WriteLine(res);

    }

      public static int CountNumbersWithUniqueDigits(int n) {               

        int cnt = 0;

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

        Combin(res, 0, n + 1, ref cnt);

        return cnt;

    }

​

    static void Combin(List<int> comb, int start, int n, ref int cnt)

    {       

        if (comb.Count == n - 1)

        {

            cnt++;

            Console.WriteLine(string.Join(" ", comb));

            return;

        }

​

        for(int i=start; i<=9; i++)

        {               

            if (comb.Contains(i) && i != 0)

                continue;           

            comb.Add(i);

            Combin(comb, start, n, ref cnt);

            comb.RemoveAt(comb.Count - 1);

        }

​

        return;   

    }

}