Numbers - formula for scheduling a timetable - Help needed!

Hello,

Any help on this would be much appreciated, It has melted my brain all day.

For the course I am studying, there is a weekly timetable made of 20 individual classes, each on 4 times a week. I would like to know how to make a spreadsheet so I can manually input all these classes and have it return a non conflicting pattern. By that I mean that I want a personal timetable that will let me visit each class at least once a week.

As I mentioned, any help would be really appreciated! Thanks!