#98

Validate Binary Search Tree

expert · 1065 · lc medium +32 · verified · 35.4% accepted · 18,287 likes · top 13%

Description

Determine whether the binary tree rooted at root is a valid BST. A valid BST requires every node's left subtree to hold only keys strictly less than that node's key, its right subtree to hold only keys strictly greater, and both subtrees to be valid BSTs.

Example 1:

Input: root = [2,1,3]

Output: true

Example 2:

Input: root = [5,1,4,null,null,3,6]

Output: false

Explanation: The root node's value is 5 but its right child's value is 4.

Code

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isValidBST(self, root: Optional[TreeNode]) -> bool:

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isValidBST(self, root: Optional[TreeNode]) -> bool: