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 [] G = new int[n+1];
    G[0] = G[1] = 1;

    for(int i=2; i<=n; ++i) {
        for(int j=1; j<=i; ++j) {
            G[i] += G[j-1] * G[i-j];
        }
    }

    return G[n];
}
}