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

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