There is nothing that dictates that you use a stack when designing a FSM. I&#x27;m not going to argue that a BT wouldn&#x27;t be a good solution, I&#x27;m sure it can be used to make a reasonable one.<p>In any case, a well designed FSM would get you a long way. Since the input (pressed buttons) is finite, you can cover every single case and weight according to importance of floor and wait time.