for循环0,1,1,2,2可以组成多少个不重复的五位数？

今天想到了一个比较有意思的for循环题：0,1,1,2,2可以组成多少个不重复的五位数？

它主要是for循环多层嵌套外加if判断，代码如下：

 protected void Button1_Click(object sender, EventArgs e)
        {
            List<string> list = new List<string>();
            string[] ss = { "0","1","1","2","2" };
            string str = "";
            //万位
            for (int i = 1; i < 5; i++)
            {
                //千位
                for (int k = 0; k < 5; k++)
                {
                    if (i != k) 
                    {
                        //百位
                        for (int m = 0; m < 5; m++)
                        {
                            if (i != m & k != m) 
                            {
                                //十位
                                for (int n = 0; n < 5; n++)
                                {
                                    if (i != n & k != n & m != n) 
                                    {
                                        //个位
                                        for (int x = 0; x < 5; x++)
                                        {
                                            if (i != x & k != x & m != x & n != x) 
                                            {
                                                str = ss[i] + ss[k] + ss[m] + ss[n] + ss[x];
                                                //判断是否重复
                                                bool b = true;
                                                for (int y = 0; y < list.Count; y++)
                                                {
                                                    if (str == list[y])
                                                    {
                                                        b = false;
                                                    }
                                                }
                                                if (b == true)
                                                {
                                                   
                                                    list.Add(str);
                                                   
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }

                
            }
            Label2.Text = "结果是：" + list.Count.ToString();
        }