def rotate_right(self, old_root: BinaryTreeNode):
new_root = old_root.left
# 1.change upper relationships.
if old_root.is_root():
self.set_root(new_root)
else:
old_root.parent.set_child(new_root)
# 2.change old_root's left
old_root.set_left(new_root.right)
# 3.change new_root's right
new_root.set_right(old_root)
# 4.update two node's size
old_root.update_size()
new_root.update_size()
# 5.change balance factor
old_root.balance_factor = old_root.balance_factor - 1 - max(0, new_root.balance_factor)
new_root.balance_factor = new_root.balance_factor + 1 + max(0, old_root.balance_factor)
