Was that 3-4 mins from first starting to read it to finishing a solution? If so then great, but personally I would've taken 10-15 minutes because I'd be carefully reading it first and wondering why it sounds so simple.

I think it took me 9-10 mins in total, including testing on the provided inputs. I think I could have done it in a few mins faster 15 years ago when I competed (never made it to the Finals though). Also typically: one of the team members would immediately start coding up the first problem while others are working on the next problems, with the assumption that the first one is quite simple.