Leetcode•Aug 27, 2025
Unique Binary Search Trees
Hazrat Ali
Leetcode
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
Solution
/**
*
* @param {number} n
* @return {number}
*/
const numTrees = n => {
if (n <= 0) {
return 0;
}
const dp = [1];
for (let i = 1; i <= n; i++) {
let count = 0;
for (let j = 1; j <= i; j++) {
count += dp[j - 1] * dp[i - j];
}
dp[i] = count;
}
return dp[n];
};