LeetCoder - 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 c[] = new int[n+1];
        c[0] = 1;
        c[1] = 1;
        for(int i=2;i<n+1;i++) {
            for(int j=0;j<i;j++) {
                c[i] += c[j] * c[i-j-1];
            }
        }
        return c[n];
    }
}