验证二叉搜索树

class TreeNode:
    def __init__(____):
        self.val = val
        self.left = left
        self.right = right

def solve():
    def isValidBST(____):
        def validate(____):
            if not node:
                return True
            if node.val <= low or node.val >= high:
                return False
            return validate(____) and validate(____)
        return validate(root, float(____), float(____))
    root = TreeNode(____, TreeNode(____), TreeNode(____))
    print(isValidBST(____))