leetcode 98. 验证二叉搜索树

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解题思路

判断每个节点的值是否在 (l, r) 范围内 （开区间）

代码

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# 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: TreeNode) -> bool:
        return self.solve(root)
    
    def solve(self, root, lower=-float('INF'), upper=float('INF')):
        if not root:
            return True
        
        if not (lower < root.val < upper):
            return False

        if not self.solve(root.left, lower, root.val):
            return False

        if not self.solve(root.right, root.val, upper):
            return False
        
        return True