I think it's stupid to assume that a decision regarding time complexity would never come up at their job. Where I work right now, and especially in Google (not where I work right now), it is important that one understands time and space complexity issues well. The data sizes are huge and optimization skills are highly valued.

Sure I can teach constant vs. linear time. But what incentive or reason do I have to spend time teaching these fundamental concepts when I can just hire an engineer who demonstrates the understanding of basic CS at the interview time itself?

Given two candidates with all things equal except that one demonstrates the understanding of CS fundamentals and other does not, why would I want to hire the second person and spend our time teaching him those concepts?

>why would I want to hire the second person and ...

Someone commented on here recently that they would take motivated candidates over knowledgeable candidates. That's one reason. I can easily think of at least two others.

There are balance points here that vary according to all sorts of things.

I said, "Given two candidates with all things equal except ..."

I mean if there are two candidates who are equally motivated and are more or less equal in all things except that one is strong at CS fundamentals and another isn't, is there a good reason to reject the candidate who is good at CS fundamentals.

In many hiring decisions, I am faced with a similar choice, and I go for the person who is good at CS fundamentals. If two candidates are good in all other ways, then the understanding of CS fundamentals becomes a tie breaker. I see no rationale for selecting the guy who does not demonstrate his strength in CS fundamentals.

I don't really agree ... doing thing A well usually means understanding B, C and D which underpin A. It's actually quite useful to ask people about B, C and D because if you only ask them to do A you don't know if they are doing A the right way because they really know what they are talking about or if they are just cargo culting something they pretend to understand but have no deep knowledge of.

With most people, it is impossible to gauge how good they are just by observing what they do in half a day on the job. Thus, any interview process must necessarily be somewhat artificial in trying to gain insight into a candidate's abilities in the span of a half a day.

A real life task might be implementing a much more complex library over several days or weeks. Asking the person to implement a simple function like shuffle is the closest you can get in the span of an hour.