c# 生成随机N位数字串（每位都不重复）

 /// <summary>
        /// 生成随机数字窜
        /// </summary>
        /// <param name="Digit">位数</param>
        /// <returns></returns>
        private string RandomNum(int Digit)
        {
            ArrayList MyArray = new ArrayList();
            Random random = new Random();
            string str = null;
            int Nums = Digit;
            while (Nums > 0)
            {
                int i = random.Next(1, 10);// 9>=a>=1
                if (!MyArray.Contains(i))
                {
                    if (MyArray.Count < 6)
                    {
                        MyArray.Add(i);
                    }
                    Nums -= 1;
                }
            }
            for (int j = 0; j <= MyArray.Count - 1; j++)
            {
                str += MyArray[j].ToString();
            }
            return str;
        }