求入棧順序爲1234……N的序列的全部可能的出棧序列

---

class Program
{
    private static void Fun(int x, int n, Stack<int> stack, List<int> outList,ref int count)
    {
        if (outList.Count == n)
        {
            count++;
            Console.WriteLine(string.Join(',', outList));
        }

        if (x <= n)
        {
            stack.Push(x);
            Fun(x + 1, n, stack, outList, ref count);
            stack.Pop();
        }

        if(stack.Count > 0)
        {
            var temp = stack.Peek();

            stack.Pop();
            outList.Add(temp);

            Fun(x, n, stack, outList, ref count);

            stack.Push(temp);
            outList.RemoveAt(outList.Count - 1);
        }
    }

    static void Main(string[] args)
    {
        int n;
        string nStr;
        while (true)
        {
            while (true)
            {
                Console.WriteLine("輸入一個正整數：");
                nStr = Console.ReadLine();
                if (int.TryParse(nStr, out n))
                {
                    break;
                }
            }

            var stack = new Stack<int>();
            var outList = new List<int>();
            int count = 0;
            Fun(1, n, stack, outList, ref count);
            Console.WriteLine($"總計{count}種出棧方式。");
        }
    }
}