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Comment by dinedal | Hacker News Reader

I use the "Build me a system that controls elevators" as an interview task. It's saddening how many I've interviewed that can't even get me a naive case of all destination floors get shoved on a FIFO queue. If we even get to the discussion on optimizing I've usually already decided to recommend the candidate for hiring.

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This. I used to use it, too. We would start with trivial cases (one elevator, two stories), and gradually add more floors and elevator shafts. We never, ever got to the interesting algorithms. It took a surprisingly long for people to describe anything remotely like a working, naive algorithm.

(of course, the most simple algorithm doesn't even use a queue! It just moves the elevator up until it hits the top, and down until it hits the bottom, opening the doors wherever there's a call request)

it's interesting because I just got the elevator question for the first time a month or two ago and was still scratching my head trying to figure out where the decision point on that question is. i ended up spending about half the interview talking about different ways to optimize for minimal waiting time, but now it seems like that may have just been banter after we'd covered the FIFO queue.

I try to guide my candidates to produce a functional solution before premature optimization. Obviously once a candidate proves they can come up with at least the simplest case, it's good to get an idea how how they'd optimize it, but since it turns out only 1 out of every 10 candidates actually get that far, the fact that we're having that conversation is enough to push them above the competition.

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