It's simple, unless you're given a specific broader context (like we have an enterprise customer data pruning system that needs to handle a broad range of corner cases) then you must not resort to overengineering this early in an interview.

This is a good example of being bad at writing code.

And an extra import. also, it sounds like they where looking specifically for knowledge of built-in operators.

You have a problem, so you try to solve it with a regex. You now have two problems.