组合问题

将5个小球进行组合，每次取出4个，问一共有多少种取法，将每一种情况列出来。。。？

先将情况列出来。。。。

 

下面是代码：

private void button1_Click(object sender, EventArgs e)

        {

            ArrayList al = new ArrayList();

            string str = "abcde";

            int i = 0;

            int a = 0;

            int b = 0;

            int c = 0;

 

            for (i = 0; i < str.Length; i++)//第1个数取值

            {

                for (a = i + 1; a < str.Length; a++)//第2个数取值

                {

                    for (b = a + 1; b < str.Length; b++)//第3个数取值

                    {

                        for (c = b + 1; c < str.Length; c++)//第4个数取值

                        {

                            al.Add(str[i].ToString() + str[a].ToString() + str[b].ToString() + str[c].ToString());

                        }

                    }

                }

            }

        }