[DigitalSea]

No offence to Twitter, but this is a seriously bad way of hiring developers. What are you trying to recruit mathematics scholars as developers? When will companies like Twitter learn not all great developers are math geniuses? I didn't even get a college education to get where I am, I failed maths in school as well, but I can code, so what does that mean? I think it means nothing in the greater scheme of things. By the sounds of it the author got a better position in the end, I'd rather be working at Amazon who are solving much better problems than Twitter ever will likely solve anyway.

If a company (no matter how great they were) tried asking me these kinds of questions, I would immediately stop the interview and thank them for the opportunity.

[bloometal]

I have no idea why a bunch of people here keep saying these questions are good for recruiting 'mathematics scholars'. Fact: I am a mathematics graduate student and I would not be able to solve this problem. I hope there isn't a notion that people studying mathematics spend all their time solving Project Euler type questions.

In fact I would be thrilled if they are recruiting for math people. They are not. I have been in the job market for a while now and recruiters literally stop listening when they don't hear "CS" in the first sentence.

[onion2k]

"this is a seriously bad way of hiring developers"

We can't reasonably assume that Twitter uses this sort of question in all their developer interviews. We don't have enough data for that. Perhaps this guy was going for a role where solving problems quickly and under pressure was a key requirement. If that were the case, this is pretty much a perfect interview question.

[smsm42]

I have hard time imagining what position, at least if we're talking about software engineering, would require solving abstract toy problems in a timeframe of less than an hour without a chance to ever go back and improve your solution. I'd say it's "did you see this problem before" kind of question. Which means Twitter probably lost a capable and smart hire because he couldn't quickly give a perfect answer to useless puzzle (unless of course he was hired to repair the roof in Twitter's office and solving this puzzle is required for Twitter to survive the rainy season). Hardly a "perfect" way.

[etler]

Twitter interview puzzle creator?

[smsm42]

You can take months to create puzzles, there's no pressure here.

[stefan_kendall]

The problem is that this is a bread and butter ACM problem. Anyone who has competed will know the solution. And biasing for ACM competitors is awful.

[codenut]

What made you say that twitter is trying to recruit math genius? The author's solution involves calculus while the intended solution is only a loop and some if statements. I actually like interview problems like that. It requires critical thinking which shows how the candidates think and it is also almost impossible to google.

[raverbashing]

Well, you may want to hire math scholars. I think it's important to have some in your team.

But it's also important to focus on other aspects as well.