递归计算Ackermenn函数

https://pintia.cn/problem-sets/12/problems/355

 1 int Ack(int m, int n)
 2 {
 3     int ret;
 4 
 5     if (m == 0)
 6     {
 7         ret = n + 1;
 8     }
 9     else if (n == 0 && m > 0)
10     {
11         ret = Ack(m - 1, 1);
12     }
13     else if (m > 0 && n > 0)
14     {
15         ret = Ack(m - 1, Ack(m, n - 1));
16     }
17 
18     return ret;
19 }