We all learn at different speeds and many times the speed we learn at is proportional to the time we spend. If your life is busy and you only get a little bit of time to spend on this, the natural result is that it'll take longer to learn. That's natural and there's nothing wrong with that. I do applaud your willingness to hang in there and continue; I'm sure that determination will get you where you want eventually.

As to your problem, looking at and understanding classic problems is a decent way to learn. Many of us wouldn't solve it that way, but that's because we're probably trying to solve a business problem and not teach ourselves something. We'll grab the first thing that works and use it.

As I'm lazy, I'd probably just use the hash and do:

@arr = ( ...as defined in the problem... );
%h = map { $_ => undef } @arr;
print join(" , ",keys(%h)), "\n"';
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There's probably even a way to do that in 1 line, but again, I'm lazy. :)

Besides all the other good advice you've been given, I'll add 1 more I didn't see (my apologies to anyone if I overlooked this in your post).

I believe someone did say they keep snippets of code, which we all do, but I'll advise you to go further. I actually keep a notebook of code examples and explanations from PerlMonks/blogs/web-searches/books/etc for reference, not to mention little things I've found on my own over time that are helpful. I put it in an electronic notebook for easy searching and organization (I use OneNote, but use whatever works for you). It's grown over the years and has become a helpful companion along the way -- a trusty toolbox of tips and tricks and reminders.

Good luck in your journey, and sign up and join us here too. :)