Unique Binary Search Trees.md

Given n, how many structurally unique BST's (binary search trees) that store values 1 ... n?

Example:

Input: 3 Output: 5 Explanation: Given n = 3, there are a total of 5 unique BST's:

1 3 3 2 1 \ / / / \
3 2 1 1 3 2 / / \
2 1 2 3 My code:

class Solution:
    def numTrees(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n==0:
            return 0
        self.matrix=[[-1 for m in range(n)] for m in range(n)]
        count=self.Set_node(1,n)
        return int(count)
    def Set_node(self,start,end):
        if start>end:
            return 1
        
        if self.matrix[start-1][end-1]!=-1:
            return self.matrix[start-1][end-1]
        all_trees=0
        for i in range(start,end+1):
            left_trees=self.Set_node(start,i-1)
            right_trees=self.Set_node(i+1,end)
            all_trees+=left_trees*right_trees
        self.matrix[start-1][end-1]=all_trees
        return all_trees

Solution: https://leetcode.com/problems/unique-binary-search-trees/