Ah haha I hate that question
It should be banned everywhere, oh well.
I once saw a physicist (not even a coder) give a really cool answer to it though, I wish I could remember it.
Guy Steele gave an incredibly interesting guest talk[1] at google about four different ways to solve this exact problem, and the fact that it's an interesting enough topic for an hour long google talk should probably be a clue that you shouldn't be expected to invent the best solution on the whiteboard in 40 minutes.
+/((⌽⌈\⌽a)⌊⌈\a)-a
I want to screen people for the skills that they will really need in their daily lives, so that's where I draw my pool of questions from. For example, processing data in the most simple ways (sorting, searching, extracting) quickly reveals if the candidates have actually _done_ what they claim they did. You'd be surprised how many Oxford PhDs struggle to write done a pipeline for extracting a simple word frequency list.
Now you might say "Maybe they're Windows people, or prefer Python." and my response is "I don't mind what tools you use - but you need to demonstrate that you can solve easy/common tasks on the spot, without wasting have a calendar day to re-invent the wheel."
Curious that he gave that talk about parallelism in the end of 2015, and talked about how we'll engineer more systems to enable parallelism.
First question at the end was actually whether we can get this into existing languages because new languages are "notoriously hard to get accepted."
I'm currently learning Rust and now I'm wondering how the iterator map() and other "accumulation style" functions are implemented and whether there's a way to make these parallel, since the map() call treats things independently and a sum() could be done in the proposed tree style way.
Guess I have a piece of code to look up in the standard library :)