Yeah, those kind of questions are silly and don’t reflect problems that happen in real life.
My advice when you get a question similar to this is to have a pen and paper at hand. Draw a few easy examples and find a solve those systematically by hand. From there you go to harder and harder examples and adapt your system for those examples. Try to find examples where your system fails.
Once you’re confident you’ve found all corner cases you can start to write down the algorithm.