I agree, but how is applying pre-learned algorithms significantly better than using pre-build libraries? Both is about using an existing solution, instead of coming up with it on your own. The real approach would be to ask candidates to solve a problem that doesn't easily fit into any popular category, so that they have to come up with an original approach - but that is first hard to come up with, and 2nd it would require investing extra time on both sides, which usually neither candidates nor interviewer can afford.
Yes, that's a good point, and in our interviews we do try to take a slightly less well-known problem, at least one that doesn't have a dozen well-known named algorithms.
Still, even using a pre-learned algorithm demonstrates some level of confort with algorithms in general, and can be used as a stepping stone during the interview to shift the problem slightly to see how they adapt the algorithm.
For example, if a candidate is clearly taking their time and essentially working out the algorithm themselves, and succeeding, that demonstrates the skill and we can move to other problems. If the candidate just breezes through and finishes in 2 minutes, then we can change the problem ad-hoc to try to get them off the beaten track a bit (say, if they wrote quicksort, maybe ask about making it stable, or sorting even numbers differently from odd numbers, off the top of my head).
