LeetCode-in-All

96. Unique Binary Search Trees

Medium

Given an integer n, return the number of structurally unique BST’s (binary search trees) which has exactly n nodes of unique values from 1 to n.

Example 1:

Input: n = 3

Output: 5

Example 2:

Input: n = 1

Output: 1

Constraints:

Solution

class Solution {
    fun numTrees(n: Int): Int {
        var result: Long = 1
        for (i in 0 until n) {
            result *= 2L * n - i
            result /= (i + 1).toLong()
        }
        result /= (n + 1).toLong()
        return result.toInt()
    }
}