Validate Binary Search Tree - Leetcode 98 - Python

 98. Validate Binary Search Tree

Given the root of a binary tree, determine if it is a valid binary search tree (BST).

A valid BST is defined as follows:

The left subtree of a node contains only nodes with keys less than the node's key.

The right subtree of a node contains only nodes with keys greater than the node's key.

Both the left and right subtrees must also be binary search trees.

class Solution:

    def isValidBST(self, root: Optional[TreeNode]) -> bool:

        def valid(node, left, right):

            if not node:

                return True

            if not (node.val < right and node.val > left):

                return False

            

            return (valid(node.left, left, node.val) and valid(node.right, node.val, right))

        

        return valid(root, float("-inf"), float("inf"))

Explaination :