Unique binary search trees

class Solution:
    def numTrees(self, n: int) -> int:
        dp = [0] * (n + 1)
        dp[0] = 1
        dp[1] = 1
        for i in range(2, n + 1):
            for j in range(i):
                dp[i] += dp[j] * dp[i - j - 1]
        # print(dp)
        return dp[n]

Unique Binary Search Trees

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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