Yeah, I'm disagreeing with some approaches. For example, in real life the engineer usually knows the constraints of the problem, and can add them himself. More, asking clarifying questions regarding memory versus speed will quite often draw blanks from less-technical consumer. Some aspects of the problem seem artificial - do we need exactly two days visits to be loyal? Exactly two unique pages? What one's going to do tomorrow, when these requirements change? And that would affect the design chosen.

I feel that author filtered out lots of great candidates over this problem, which might be something to pause about. On the other hand, interviewing to get a good signal is indeed a tricky business, so I can sympathize.