I think this is a reasonable question, probably better for students who still remember their O's and Tries but reasonable enough for the intermediate quality solution -- an engineer who cannot even solve the simpler version probably cannot write algorithms at all.

That said, from the article this article links to, I find this puzzling:

> The candidate’s performance on the problem isn’t binary. The worst candidates don’t even manage to implement the fizzbuzz solution in 45 minutes. The best implement a memoized solution in 10 minutes, allowing you to make the problem even more interesting, e.g., asking how they would handle a dictionary too large to fit in main memory. Most candidates perform somewhere in the middle.

Two things I worry about: if the interview isn't "binary", how do you decide whether the candidate passed? Is doing just the simpler version fine as long as you ask for low pay? Or are you still failed? Or does it depend on whether other candidates did better, which is another way of saying you failed? It seems to me it's still binary.

And the other thing is: if the candidate did great in 10', please don't ask additional questions. The candidate is a "hire". Don't make it "interesting", an interview is not the place to shake things up to make it "interesting". Understand that for most people, interviewing is a stressful situation. For "interesting" times they have their friends and Netflix.