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47 lines
1.2 KiB
Plaintext
47 lines
1.2 KiB
Plaintext
---
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title: '98. Validate Binary Search Tree'
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description: Given the root of a binary tree, determine if it is a valid binary search tree (BST)
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sidebar:
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label: 'Validate Binary Search Tree'
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badge: 'Medium'
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---
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<Badge variant="accent">Binary Search Tree</Badge>
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### Example 1:
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- Input: `root = [2,1,3]`
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- Output: `true`
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### Example 2:
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- Input: `root = [5,1,4,null,null,3,6]`
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- Output: `false`
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- Explanation: The `root` node's value is `5` but its right child's value is `4`.
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### Constraints:
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- The number of nodes in the tree is in the range [1, 10^4].
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- `-2^31 <= Node.val <= 2^31 - 1`
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## Solution
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```py
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# Definition for a binary tree node.
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# class TreeNode:
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# def __init__(self, val=0, left=None, right=None):
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# self.val = val
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# self.left = left
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# self.right = right
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class Solution:
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def isValidBST(self, root: Optional[TreeNode]) -> bool:
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def valid(node, low, high):
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if not node:
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return True
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if not (low < node.val < high):
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return False
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return valid(node.left, low, node.val) and valid(node.right, node.val, high)
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return valid(root, float("-inf"), float("inf"))
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```
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