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:
1 <= n <= 19
Solution
object Solution {
def numTrees(n: Int): Int = {
var result: Long = 1L
for (i <- 0 until n) {
result *= 2L * n - i
result /= i + 1
}
result /= (n + 1)
result.toInt
}
}