C# 有放回（重复）组合算法

static List<string> GetAllZuhe(List<string> list, int n)
        {
            if (n <= 1)
            {
                return list;
            }
            else
            {
                List<string> rl = new List<string>();
                foreach (string x in list)
                {
                    foreach (string y in GetAllZuhe(list, n - 1))
                    {
                        rl.Add(x + y);
                    }
                }
                return rl;
            }
        }
    }

 static void Main(string[] args)
        {
            List<string> list = new List<string>();
            list.Add("1");
            list.Add("2");
            list.Add("3");
            list.Add("4");
            List<string> allList=GetAllZuhe(list,3 );
            Console.WriteLine(allList.Count+ "\n");
            bool flag = true;
            foreach (string s in allList)
            {
                if (flag)
                    Console.Write(s+" ");
                else
                    Console.Write(s + "\n");
                flag = !flag;
            }
            Console.ReadLine();
        }