> > Take "determine if a linked list has a cycle in it." The solution people are supposed to come up with, "Tortoise and Hare", was AFAICT published in a heavil

> > Take "determine if a linked list has a cycle in it." The solution people are supposed to come up with, "Tortoise and Hare", was AFAICT published in a heavily-cited 1967 research paper. You're asking a candidate to reinvent CS research in 30 minutes! > Well, multi-threading was a decade long research, if not more. Do you then expect folks interviewing for Android Development, say, not know about critical sections, race conditions, mutual exclusion, re-entrant locks et al because these were ironed out over decades and decades of research? Guess not. You have a point, but the other concepts you mentioned are useful in real-world development. Determining whether a linked list has a cycle in it is not. At most, you could say that similar algorithms are occasionally useful in cryptography[1], where you're looking for cycles in repeated application of a mathematical function. But for an actual linked list in memory, you usually know in advance whether it's supposed to be circular. I guess it could be used as a debugging aid in case the invariant is violated, but in practice you're more likely to end up with invalid pointers, or (for doubly linked lists) mismatched previous/next pointers, or any number of other messy conditions, than with an otherwise valid list that happens to have a cycle. [1] https://en.wikipedia.org/wiki/Cycle_detection#Applications https://en.wikipedia.org/wiki/Cycle_detection#Applications