排列组合算法怎样写
请问排列组合的算法怎样写？
比如有"A","B","C",排列组合成六种可能的结果:
"A","B","C" ; "A","C","B"
"B","A","C" ; "B","C","A"
"C","A","B" ; "C","B","A"
以后会有"A","B","C","D"
请问程序怎样写可以得出这些结果，谢谢！
------解决方案--------------------
这叫做全排列。

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;



namespace ConsoleApplication1

{

    class Program

    {

        static void Main(string[] args)

        {

            string s = "ABCD";

            List<string> list = new List<string>();

            foreach (var i in Combo(s, 4))

            {

                list = list.Union(Arrange(i)).ToList();

            }

            list.ForEach(x => Console.WriteLine(x));

        }





        static IEnumerable<string> Arrange(string source)

        {

            for (int i = 0; i < source.Length; i++)

            {

                if (source.Length == 1)

                {

                    yield return source;

                }

                else

                {

                    foreach (var x in Arrange(source.Substring(0, i) + source.Substring(i + 1)))

                    {

                        yield return source[i] + x;

                    }

                }

            }

        }



        static IEnumerable<string> Combo(string source, int len)

     &