Is it correct to ask to solve an NP-complete problem on a job interview? [closed]

Answer 1

I prefer asking them to prove that P != NP or P == NP. Someday a candidate will answer it, I'll steal their answer and be famous!

On a more serious note, though, I think it's completely fair. Most NP complete problems are easy to solve, they just run very slowly. Unless the job requires them to know a lot about complexity theory, though, all they need to demonstrate is that they understand the solution will be slow. Bonus points if they know it's non-polynomial time, gold star if they know it's NP complete.

Answer 2

Completely legitimate to me. If you are Computer Science professional there are good chances that you can either argument informally why the problem seems to be hard, or (even better) provide a sketch of reduction from a known NP-hard problem.

Many real world problems eventually turn out to be NP-hard, and stackoverflow also has now and then questions about the complexity of a problem which turns out to be a difficult one (NP-hard, for instance). It is an important part of a CS professionals toolbox to be able to recognize and to argue for problems which are known to be difficult to solve.

Answer 3

That is evil!

If the interviewer asks an NP-complete question in an interviewer the only response they can reasonably expect is that the interviewee respond with a proof that the problem is NP-complete. In a low-stress environment like a university homework question, this usually takes a bright student 2-3 or more hours to prove. The proof itself can take several pages to write out completely, perhaps several hours of work itself. In a high-stress environment like an interview you can expect that the interviewee may not even recognize that this is np-complete.

The only reasonable alternative is that the interviewee produce an approximation algorithm; however, in this case the interviewer should make it explicitly clear that they are fine with approximations.

Even so, most approximations only come with an order of 2 of the correct answer.

I guess there is 1 more alternative: the interviewee suggests that a search-type algorithm maybe the most suitable (take for example the integer-domain optimization problem which is NP-complete, most approximation algorithms use a branch and bound search spin on the simplex algorithm to produce decent results.)

Answer 4

There's a category of interview questions that are illegal in some countries, usually pertaining to personal details that are none of the employer's business. That aside, any question is fair game if the interviewer feels it'll help get an idea of the interviewee's capabilities!

If you're hiring for a position that calls for a thinker rather than just a code monkey, it may be useful to throw this kind of problem at the applicant. Who cares if a problem is "well known" to be NP? If the guy is good he'll come to that understanding in analyzing the problem. That may well be the result the interviewer wants to see, or the applicant can go on to do some more pre-analysis and describe how he'd brute-force the problem, or what optimizations he can think to apply to make it more manageable.

Answer 5

It's sort of mean to ask nigh-impossible questions without informing the interviewee of it, but in observed problem solving, the question is often asked so that you may demonstrate critical thinking skills, how you approach problem solving, and how you handle pressure or failure.

I've been asked interview questions I couldn't solve, and I don't think I've ever "failed" an interview because of it.

Answer 6

If such a question was given before an interview(to be answered at an interview) I would say it's ok.. but to just solve such a difficult problem as that on the spot is definitely not going to be done well by any programmer, and if the programmer does do it well that just means they can act on the spot(which isn't always the best thing for programming as designing things needs to take time and check every possible flaw) or that they have seen a similar problem before.

Edit: Or possibly discussion about the problem would be good, like say laying down a plan of action whether or not you completely solve it.. and discussing how feasible and if there is a fast(but difficult) way to do it and such. I would not say that the interviewee should have to write down over 50 lines of C code in an interview to solve it though