Unique Binary Search Trees 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

Solution: dp.
http://fisherlei.blogspot.com/2013/03/leetcode-unique-binary-search-trees.html

class Solution {
public:
    int numTrees(int n) {
        vector<int> dp(n+1, 0);
        dp[0] = 1;
        dp[1] = 1;
        for(int i = 2; i <= n; i++) {
            for(int j = 0; j < i; j++) {
                dp[i] += dp[j] * dp[i-j-1];
            }
        }
        return dp[n];
    }
};