96. Unique Binary Search Trees

Given n, how many structurally unique BST’s (binary search trees) that store values 1 … n?

Example:

Input: 3 Output: 5 Explanation: 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

DP：

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