[Leetcode] Unique BST I

Given n, how many structurally unique BST's (binary search trees) that store values 1...n?

For example,
Given n = 3, there are a total of 5 unique BST's.

   1         3     3      2      1    \       /     /      / \      \     3     2     1      1   3      2    /     /       \                 \   2     1         2                 3

class Solution {public:    int numTrees(int n) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(n==1) return 1;        if(n==0) return 1;        int count = 0;        int equal = 0;                for(int i=0;i<n;i++)        {            count += numTrees(i) * numTrees(n-i-1); //太懒，用了递归。用DP写应该更好一些。        }                return count;            }};