The test is composed of multiple levels that you have to solve in ascending order, in the language of your choice. Please try to do the simplest thing to solve the level you're currently working on, and not over engineer things. As the complexity increases after each level, you'll eventually need to re-use some code, refactor it and add layers of abstraction using OOP and/or functional programming.
What we're interested to see:
- Code that works :)
- Clean code
- Good levels of abstraction when needed
- Robust to errors (use exceptions and errors, think about corner cases)
- User oriented code (you have to make users happy)