LeetCode-Unique Binary Search Trees

同上一道返回bst树的题目的思路，

求数目的话更加简单；

 1 class Solution {
 2 public:
 3     int numTrees(int n) {
 4         // Start typing your C/C++ solution below
 5         // DO NOT write int main() function
 6         if (n <= 0) {
 7             return 0;
 8         }
 9         int count = 0;
10         getNum(count, 1, n + 1);
11         return count;
12     }
13     void getNum(int &count, int l, int r) {
14         if (l == r) {
15             count = 1;
16             return;
17         }
18         for (int i = l; i < r; ++i) {
19             int left = 0;
20             getNum(left, l, i);
21             int right = 0;
22             getNum(right, i + 1, r);
23             count += left * right;
24         }
25     }
26 };

 

posted @ 2013-09-09 22:54  Exio  阅读(182)  评论(0)  编辑  收藏  举报