#98

Validate Binary Search Tree

medium· Treesruns: 0

Given the root of a binary tree, determine if it is a valid binary search tree. A valid BST is one where the left subtree of every node contains only values less than the node's value, the right subtree contains only values greater, and both subtrees are themselves BSTs.

wpm 0acc 100%time 0:000 / 472

class Solution:
    def isValidBST(self, root: TreeNode | None) -> bool:
        def valid(
            node: TreeNode | None, low: float, high: float
        ) -> bool:
            if not node:
                return True
            if not (low < node.val < high):
                return False
            return valid(node.left, low, node.val) and valid(
                node.right, node.val, high
            )

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

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