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 class Solution { public int numTrees(int n) { int countUniqueTrees[] = new int[n + 1]; countUniqueTrees[0] = 1; countUniqueTrees[1] = 1; for (int i = 2; i <= n; i++) { for (int j = 1; j <= i; j++) { countUniqueTrees[i] = countUniqueTrees[i] + (countUniqueTrees[i - j] * countUniqueTrees[j - 1]); } } return countUniqueTrees[n]; } } Try it on Leetcode The idea behind solving this problem is , for all possible values of i, consider i as root, such that 1....i-1 will com