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98.ValidateBinarySearchTree(2nd).py
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98.ValidateBinarySearchTree(2nd).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.
Example:
5
/ \
1 4
/ \
3 6
Input: [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.
"""
#Difficulty: Medium
#75 / 75 test cases passed.
#Runtime: 60 ms
#Memory Usage: 16.1 MB
#Runtime: 60 ms, faster than 23.93% of Python3 online submissions for Validate Binary Search Tree.
#Memory Usage: 16.1 MB, less than 74.97% of Python3 online submissions for Validate Binary Search Tree.
class Solution:
def isValidBST(self, root: TreeNode) -> bool:
order = []
self.validator(root, order)
for i in range(1, len(order)):
if order[i-1] >= order[i]:
return False
return True
def validator(self, root, order):
if not root:
return 0
self.validator(root.left, order)
order.append(root.val)
self.validator(root.right, order)