排列组合算法怎样写,该如何解决

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！

[解决办法]
这叫做全排列。

C# code

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)        {            int[] pos = new int[len];            for (int i = 0; i < len; i++) pos[i] = i;            while (pos[0] < source.Length - len)            {                string str = "";                for (int i = 0; i < len; i++) str += source[pos[i]];                for (int i = len - 1; i >= 0; i--)                {                    if (pos[i] < source.Length - len + i)                    {                        pos[i]++;                        for (int j = i + 1; j <= len - 1; j++)                        {                            pos[j] = pos[i] + j - i;                        }                        break;                    }                    else                    {                        continue;                    }                }                yield return str;            }            yield return source.Substring(source.Length - len);        }    }}
[解决办法]
另外，写为Linq查询表达式也是一样的。因为Linq也会使用yield迭代器来延迟计算，所以不用担心Linq的效率问题。使用Linq看起来逻辑上更优雅：
C# code
using System;using System.Collections.Generic;using System.Linq;namespace ConsoleApplication1{    class Program    {        static void Main(string[] args)        {            排列组合("ABC", 0, 3).ToList().ForEach(x => { Console.WriteLine(x); });            Console.ReadKey();        }        private static IEnumerable<string> 排列组合(string source, int fr, int len)        {            if (len == 1)                return new List<string> { source.Substring(fr, 1) };            else                return from sub in 排列组合(source, fr + 1, len - 1)                       from i in Enumerable.Range(0, sub.Length + 1)                       let first = source.Substring(fr, 1)                       select sub.Insert(i, first);        }    }}