从0到n的排列的一种求法

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从0到n的排列的一种求法（效率低，急需改进）

用到了split和backgroundWorker。textbox用来接收输入，lixtbox输出。button开始计算。

private void button1_Click(object sender, EventArgs e)
        {
            int needtocal = int.Parse(textBox1.Text);
            backgroundWorker1.RunWorkerAsync(needtocal);

}

        //计算
        public string CalPermutation(int n)
        {
            string result = "";
            if (n < 0) return "";
            if (n == 0)
            {
                result = "0";
            }
            else if (n == 1)
            {
                result = "01,10";
            }
            else
            {

                string last = CalPermutation(n - 1);
                string delimStr = ",";
                char[] delimiter = delimStr.ToCharArray();
                string[] split = null;
                split = last.Split(delimiter);
                foreach (string s in split)
                {
                    for (int i = 0; i < n + 1; i++)
                    {
                        if (result != "")
                            result += ",";
                        result += s.Insert(i, n.ToString());

                    }
                }
            }
            return result;
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker worker = sender as BackgroundWorker;
            e.Result = CalPermutation((int)e.Argument);
        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            // First, handle the case where an exception was thrown.
            if (e.Error != null)
            {
                MessageBox.Show(e.Error.Message);
            }
            else
            {
                // handle the case where the operation
                // succeeded.
                string delimStr = ",";
                char[] delimiter = delimStr.ToCharArray();
                string[] split = null;
                split = e.Result.ToString().Split(delimiter);
                foreach (string ss in split)
                {
                    listBox1.Items.Add(ss);

               }
            }
        }