[throwawaymath]

I'm fairly certain I know which company you're talking about - I'd recommend you redact the specific question they asked, because I'm aware that they do check online (including HN) for interview questions that were asked. You have plausible deniability as long as you don't name the company, but given the NDA they throw at you it's probably better to be safe than sorry :)

That being said - sorry to hear that was your experience. That shouldn't have happened, but it does.