kazi1@的部落格

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

Assume a 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.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def validate(self, root, minval, maxval):
        if root == None:
            return True
        if minval >= root.val or root.val >= maxval:
            return False
        return self.validate(root.left, minval, root.val) and self.validate(root.right, root.val, maxval)

    def isValidBST(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root is None:
            return True
        return self.validate(root, -sys.maxint-1, sys.maxint)