code: def isVaild_helper(self, root, minVal, maxVal):
      if root is None:
          return True
      if root.val >= maxVal or root.val <= minVal:
          return False
      return self.isVaild_helper(
          root.left, minVal, root.val
      ) and self.isVaild_helper(root.right, root.val, maxVal)
  
imports: import sys
label_desc: Use image node_id 2 for calling the Solution obj's underlying member method code with example usage: obj.isVaild_helper(root, minVal, maxVal) and returns: unknown, True, False