[LC] 98. Validate Binary Search Tree

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

Assume a BST is defined as follows:

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

Example 1:

Example 2:

# Definition for a binary tree node. # class TreeNode: #     def __init__(self, x): #         self.val = x #         self.left = None #         self.right = None  class Solution:     def isValidBST(self, root: TreeNode) -> bool:         import sys         right_bound = sys.maxsize         left_bound = -sys.maxsize - 1         return self.helper(root, left_bound, right_bound)              def helper(self, root, left_bound, right_bound):         if root is None:             return True         if root.val <= left_bound or root.val >= right_bound:             return False         return self.helper(root.left, left_bound, root.val) and self.helper(root.right, root.val, right_bound)                  

来源：博客园

作者：xuan_abc

链接：https://www.cnblogs.com/xuanlu/p/11683776.html