I got the first part done in under an hour.
The second part took me a lot longer (it is late in the evening on Day 8 as I write this).
I’ve been busy and haven’t had the same block of time to concentrate on it as I did for part 1. But also, I need to find sounder, less-fiddly less-haphazard tools for managing & updating many little pieces of associated state in Racket.
About the only good thing about this day’s puzzles was that I finally grokked what the let loop form does and is good for. In a nutshell: let loop lets you do for/fold without actually “iterating over” anything (i.e., no for-clause, just accumulators).
Solutions: day07.rkt