Ask your peers. As an ex-prof, one of the most prominent sources of missed potential I see in undergrads is not working with their peers. Like serious 2-6 hours sessions of collaborative problem solving.

You're right, but it depends on your peers. If you're the only one motivated to do extra work, your peers are unlikely to want to spend hours on verifying the solution. Guess it shows the importance of good peers.

Yep, I hated that. Spending an hour on a problem and get a solution you can't verify. It very much affected my motivation on starting on the problem knowing that I wouldn't know if I was right or wrong.

When I was an undergraduate we had Schaum's Outline Series (do they still exist?). Every chapter came with a bunch of completely solved problems plus another bunch of unsolved problems with the answers. The optimal strategy was still to try and do the solved problems by yourself and then verifying your solution.