递归求Fabonacci数列

https://pintia.cn/problem-sets/12/problems/356

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