[dpark]

> Not sure why employers care about developers being able to write utility functions from scratch, when that is not (typically) the job developers are hired for.

Because of the reasons you listed in your next paragraph:

> poor naming, unfamiliarity with their language's data structures, etc. Those are issues that will come up. Especially naming.

No one actually wants a candidate to write "flatten". They want the candidate to demonstrate that they can work through a small problem and write something sane and functional. Utility functions tend to be small and reasonable to put together in about an hour.

With that said, I think this is a mediocre question because no one would create this list of lists-or-ints in Java. If presented well, the problem might be decent. If presented poorly, a lot of junior candidates would likely fail even if they're good candidates.