LeetCode 98 - 验证二叉搜索树

class Solution:
    def isValidBST(self, root: Optional[TreeNode]) -> bool:
        values = []
        if not root:
            return False
        def isValidBSTimpl(root: Optional[TreeNode]):
            nonlocal values
            if not root:
                return
            isValidBSTimpl(root.left)
            values.append(root.val)
            isValidBSTimpl(root.right)
        isValidBSTimpl(root)
        return all(values[i] < values[i + 1] for i in range(len(values) - 1))