Unique Binary Search Trees

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:

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