【LeetCode】96 - Unique Binary Search Trees

 1 class Solution {
 2 public:
 3     int numTrees(int n) {
 4         if(n == 0)
 5             return 1;
 6         else if(n == 1)
 7             return 1;
 8         else
 9         {
10             int count = 0;
11             for(int i = 0; i <= (n-1)/2; i ++)
12             {
13                 if(i < n-1-i)
14                     count += 2*numTrees(i)*numTrees(n-1-i);
15                 else
16                     count += numTrees(i)*numTrees(n-1-i);
17             }
18             return count;
19         }
20     }
21 };