# 排列组合算法怎样写,该如何解决

www.MyException.Cn  网友分享于：2013-04-21  浏览：137次

"A","B","C" ; "A","C","B"
"B","A","C" ; "B","C","A"
"C","A","B" ; "C","B","A"

------解决方案--------------------

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);
}
}
}
------解决方案--------------------

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); });
}

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);
}
}
}```