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

namespace PermAndComb
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = "abcd";
            Permutation(s);
            Console.ReadKey();

        }

        public static void Permutation(string s)
        {
            int len = s.Length;
            char [] inStr  = s.ToCharArray();
            StringBuilder outStr = new StringBuilder();
            bool[] used = new bool[len];

            doPermute(inStr, outStr,used, len, 0);

        }

        public static void doPermute(char[] instr, StringBuilder outStr,bool [] used, int len, int level)
        {
            if (level == len)
            {
                Console.WriteLine(outStr.ToString());
                return;
            }

            for (int i = 0; i < len; i++)
            {
                if (used[i]) continue;
                outStr.Append(instr[i]);
                used[i] = true;
                doPermute(instr, outStr, used, len, level + 1);
                used[i] = false;
                outStr.Length = outStr.Length - 1;

            }

        }
    }
}

string str = "abcd";

Func<int, int> factorial = n =>
    Enumerable.Range(1, n)
    .Aggregate((i, j) => i * j);
Func<int, int[]> tofactoradic = n =>
    Enumerable.Range(1, n)
    .Reverse()
    .Select(i => { var m = n; n /= i; return m % i; })
    .ToArray();
Func<int[], string, string> Apply = (f, s) => {
    var chars = s.ToList();
    var result = "";
    for (int i = 0; i < s.Length; i++) {
        result += chars[f[i]];
        chars.RemoveAt(f[i]);
    }
    return result;
};

int max = factorial(str.Length);
for (int i = 0; i < max; i++ ) {
    var f = tofactoradic(i);
    Console.WriteLine(Apply(f, str));
}