Validate Binary Search Tree in Binary Tree

bytedance Given a binary tree, determine if it is a valid binary search tree (BST). A valid BST is defined as follows: For every node in the tree, all node values in its left subtree are less than the node's value, and all node values in its right subtree are greater than the node's value. The binary tree node definition is as follows: class TreeNode: def __init__(self, val=0, left=None, right=None): self.val = val self.left = left self.right = right Input-Output Example Input: root = [2,1,3] Output: True Input: root = [5,1,4,null,null,3,6] Output: False Please implement an algorithm to achieve this functionality. Example Input root = [2,1,3]