LeetCode-in-Dart
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
class Solution {
int numTrees(int n) {
int result = 1;
for (int i = 0; i < n; i++) {
result = result * (2 * n - i) ~/ (i + 1);
}
result ~/= (n + 1);
return result;
}
}