二叉搜索树中的每个结点，其左子树的所有结点值都小于该结点值，右子树的所有结点值都大于该结点值。以下代码对给定的整数数组(假设数组中没有数值相等的元素)，构造一个对应的二叉搜索树，横线上应填写（ ）: node.val, max_val)

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def isValidBST(self, root: TreeNode) -> bool:
        def helper(node, min_val, max_val):
            if not node:
                return True
            ————————————————————————————————————————————————
                return False
            return helper(node.left, min_val, node.val) and helper(node.right,

return helper(root, float('-inf'), float('inf'))