m个数字任选n个数组进行组合

using System;
using System.Collections;

namespace ConsoleApplication1
{
class Program
{
static ArrayList result = new ArrayList();
static string m="123456789";
static int n = 4;
static void Main(string[] args)
{
char[] s = m.ToCharArray();
string tmp = "";

for (int i = 0; i < s.Length; i++)
{
tmp = s[i].ToString();
int j = i + 1;

display(s, j, tmp);
}

for (int i = 0; i < result.Count; i++)
Console.WriteLine(result[i].ToString());

Console.ReadLine();
}

static void display(char[] s, int j, string ret)
{
for (; j < s.Length; j++)
{
string tmp = ret + s[j].ToString();
if (tmp.Length == n)
{
result.Add(tmp);
}

display(s, j + 1, tmp);

}
}

}
}