One of the interview questions I've used in the past is "reverse a linked list".
Indeed, you (almost) never need to reverse linked lists in practice - but you often need to chase references of one kind or another (database, pointers, etc.) and do some manipulations on them that would result in a different list. If you have 20 data points, it doesn't matter what you do, but if you have 100M or 10B points, it makes a great deal of difference whether you do O(n), O(n log n) or O(n^2) or O(n!).
I think this is a good question, because it is an abstract version of the kind of problems that any non trivial code has to address. It is easy to describe, and easy to solve if you know what you are doing. I don't use it anymore because it's too common to be useful.
And yet, through the years I've gotten the feedback[0] that it is "far detached from real work", "tests how good I did in school rather than how good I am" and various other comments -- and almost always from candidates who did poorly; I've never gotten this feedback from anyone I would consider competent.
[0] I try to get feedback through whoever referred the candidate, whether it's the friend-of-acquaintance, or the recruiter. I don't, in general, trust direct feedback from someone I turned down (or hired, for that matter).
Indeed, you (almost) never need to reverse linked lists in practice - but you often need to chase references of one kind or another (database, pointers, etc.) and do some manipulations on them that would result in a different list. If you have 20 data points, it doesn't matter what you do, but if you have 100M or 10B points, it makes a great deal of difference whether you do O(n), O(n log n) or O(n^2) or O(n!).
I think this is a good question, because it is an abstract version of the kind of problems that any non trivial code has to address. It is easy to describe, and easy to solve if you know what you are doing. I don't use it anymore because it's too common to be useful.
And yet, through the years I've gotten the feedback[0] that it is "far detached from real work", "tests how good I did in school rather than how good I am" and various other comments -- and almost always from candidates who did poorly; I've never gotten this feedback from anyone I would consider competent.
[0] I try to get feedback through whoever referred the candidate, whether it's the friend-of-acquaintance, or the recruiter. I don't, in general, trust direct feedback from someone I turned down (or hired, for that matter).