Cisco Intern - Software Engineer interview questions

A sawmill has a conveyor belt that transports wood out of the mill. The mill has to types of wood blocks (long - 30cm, short - 25cm), you are given two sensors which you can place on top of the conveyor belt which notifies your program every time their state is changed. You can set up the sensors at every position you want, at the end of the day your program should be able to return the number of short and long wood blocks processed during this day.