oh, this made me feel dumb. Its so simple.

Same. I just wrote it in the order I thought it out though -- put the difficult part on the left, then filled in the simple part on the right. Would have changed it if I looked at it for more than a few seconds before submitting.

Honestly, I think it has to do with reading comprehension. I submitted this solution as well, yet for some reason I find the other one easier to read at a glance.

"set() method is used to convert any of the iterable to sequence of iterable elements with distinct elements, commonly called Set."
Meaning, a set is the same basic group of characters as the original, except it excludes duplicates and it is not in order.

Do you really need to ask? https://www.google.com/search?client=firefox-b-e&q=python+set

Ive seen people use the set() function for this. what does it do?

else here is unnecessary, either is double return, however the best practices in comparison to other answers anyway.