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validate-binary-search-tree.py
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validate-binary-search-tree.py
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# 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.
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
# here is the video explanation of this : https://www.youtube.com/watch?v=MILxfAbIhrE
class Solution(object):
def isValidBST(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
sys_max , sys_min = float("inf"), float("-inf")
return self.isBST(root,sys_min,sys_max)
def isBST(self, root , min,max):
if root is None :
return True
if min < root.val or root.val < max:
return False
else:
return self.isBST(root.left,min,root.val) and \
self.isBST(root.right,root.val,max)