LeetCode Q96: 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:
Different from Unique Binary Search Trees II problem, in this problem, there is no need to know exact information contained in each node. All we need to know is for a given number of nodes, how many different unique BST can be generated. The solution is very similar to Fibonacci sequence problem.