算法-字符全排列

1 递归实现字符串的全排列

    protected void Page_Load(object sender, EventArgs e)
    {
        ArrayList strArray = new ArrayList() { "a", "b", "c" ,"d"};
        AllArrangement(strArray);
    }
    //全排列
    //递归实现 当前实现需要下一层返回支持
    private ArrayList AllArrangement(ArrayList strArray)
    {
        ArrayList a_Recursion = new ArrayList();//递归数组
        ArrayList a_print = new ArrayList();//显示数组
        //中止条件 有返回值 或者  无返回值
        if (strArray.Count == 2)
        {
            a_Recursion.Add(strArray[0].ToString() + strArray[1].ToString());
            a_Recursion.Add(strArray[1].ToString() + strArray[0].ToString());
            return a_Recursion;
        }
        //生成递归条件
        for (int i = 1; i < strArray.Count; i++)
        {
            a_Recursion.Add(strArray[i]);
        }
        a_Recursion = AllArrangement(a_Recursion);
        //交换并打印 利用返回的数组，与当前层结合，显示排列的字符串
        for (int i = 0; i < a_Recursion.Count; i++)// bc  cb
        {
            a_print.Add(strArray[0].ToString() + a_Recursion[i].ToString());
            lbl.Text += (++count).ToString()+strArray[0].ToString() + a_Recursion[i].ToString() + "&nbsp;";
            for (int j = 1; j < a_Recursion[i].ToString().Length+1; j++) //bc
            {
                lbl.Text += count.ToString() + a_Recursion[i].ToString().Insert(j, strArray[0].ToString()) + "&nbsp;";
                a_print.Add(a_Recursion[i].ToString().Insert(j, strArray[0].ToString()));
            }
            lbl.Text += "<br/>";
        }
        return a_print;
    }