static string[] str = new string[] { "A1", "A2", "A3", "A4", "A5", "A7", "B1", "B3", "B5", "B6", "B7", "B8" };
        static List<string> strs = new List<string>();
        static void Main(string[] args)
        {
            Console.WriteLine("输入一个数...");
            string ss = Console.ReadLine();
            DoWork("", 0, int.Parse(ss));
            foreach (string s in strs)
            {
                Console.WriteLine(s);
            }
            Console.ReadLine();
        }

        static void DoWork(string r,int i,int t)
        {
            if (r.Length / 2 >= t)
            {
                strs.Add(r);
                return;
            }
            for (; i < str.Length;)
            {
                DoWork(r + str[i], ++i, t);
            }
        }