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
#include <stdio.h>
int numTrees(int n) {
long result = 1;
for (int i = 0; i < n; i++) {
result *= (2L * n - i);
result /= (i + 1);
}
result /= (n + 1);
return (int) result;
}