def rob(self, root: TreeNode) -> int:
if not root or root.val is None:
return 0
if getattr(root, "max_seen", False):
return root.max_seen
# rob the root
choice_1_value = root.val
if root.left and root.left.left:
choice_1_value += self.rob(root.left.left)
if root.left and root.left.right:
choice_1_value += self.rob(root.left.right)
if root.right and root.right.left:
choice_1_value += self.rob(root.right.left)
if root.right and root.right.right:
choice_1_value += self.rob(root.right.right)
# don't rob the root
choice_2_value = 0
if root.left:
choice_2_value += self.rob(root.left)
if root.right:
choice_2_value += self.rob(root.right)
maximum = max(choice_1_value, choice_2_value)
root.max_seen = maximum
return root.max_seen
