I have personally been annoyed when I cannot find solution to hard problem. I used to think that "looking up" for an answer is not being honest. That stance may not help. After trying, I think, a student (like me), could benefit by looking up the answers for hard problems, and try to emulate it.
Found this in the words a professor giving advise to his students.
Students join forces on the problem sets, and some students benefit more than others from these weekly collective efforts. The most brilliant students will invariably work out all the problems and let other students copy, and I pretend to be annoyed when I learn that this has happened. But I know that by making the effort to understand the solution of a truly difficult problem discovered by one of their peers, students learn more than they would by working out some less demanding exercise.