[addcn]

One unconventional tip for code challenges comes to mind. A candidate used it on me and it was worth a ton of points in my book.

Instead of just doing the challenge ask the interviewer what they want you to optimize for? Performance? Shortness? Readability? Maintainbility? Make it clear there are tradeoffs to each and that the tradeoffs you choose often matter more than the code itself.

As a plus you also get insights into what the company values.