[abalone]

I mostly agree with this, however if the job requires a C.S. degree or equivalent and you assume all qualified candidates have been exposed to this, then perhaps it can be a useful question for testing how well you can explain a solution.

Just look at how varied and complicated some of the explanations are for this out there. Some take mathematical approaches, others (me) try to boil it down to a few intuitive sentences... I can see it giving some insight into a candidate.

[marcus_chang]

Unless you're interviewing Dijkstra, it's a ridiculous question to ask. Anyone who's heard it before knows the answer instantly (I knew the answer before I even finished reading the description) and anyone unfamiliar with it will likely flail.

[abalone]

Nah, I wouldn't say everyone would flail but Dijkstra. There are simpler solutions to cycle detection.. maybe not as efficient as Floyd, but you could answer the question. For example you could start with something basic and unoptimized like keep a data structure of all the nodes you walk, and when you hit one that's in the structure then you've encountered a cycle. This is a fair approach to engineering solutions to novel problems -- don't panic, get something working, then optimize where necessary.

And if you already know the best practice, like I said, it's not just about whether you know the answer -- it's how simply you can explain it to a teammate and the theory behind why it works. That's also a useful skill to interview for, especially for more experienced candidates.

[mort96]

I’m not convinced anyone unfamiliar would likely fail. A pretty obvious solution is to just have a list of all nodes you’ve been to, and check if the current node is in that list. Not the most optimal solution, but one I’d imagine a lot of decent programmers would be able to come up with.

Not saying it’s a good interview question, just that most good programmers shoukd be able to come up with some form of answer if they understand linked lists.

[trhway]

>Unless you're interviewing Dijkstra, it's a ridiculous question to ask.

like many ridiculously looking interview questions, they are actually a filter. For this particular types of questions young people tend to quickly solve them. In 1987, in 9th grade, during one of the first computer classes, never before seeing or touching programming (previous years of school in a small town in USSR), I myself came up with Dijkstra algorithm in less than 10 minutes when we were assigned task of finding shortest path. I remember the teacher looking impressed :) These days i treat it more like a signal - if people asks such puzzles a lot then they either intentionally filtering or even don't understand that and seriously think it is important CS(cience).

[bpicolo]

> and you assume all qualified candidates have been exposed to this

The point is that that's an absurd thing to assume. It would almost never come up organically (and has only really come up in the context of awful interview question blogs). It's not a taught/talked about algorithm.

Rote memorization is also a poor metric for job performance.

[pjmlp]

My CS degree had a duration of 5 years, and I graduated during the 90's.

Excuse me if I don't recall a complete year of Algorithms and Data Structures lectures and evaluation projects done about 25 years ago.