Context switch in our multithreaded process, back to 2021 from 2019.
So, it's Saturday, December 18th. Can't really remember what I was up to, but an old friend phoned and he was up for a catch-up and some beer. This was around 8pm. I was dubious as from where he lives, he wouldn't get here until 10pm, but my arm was twisted.
He turned up around 9:30pm which was a surprise because he's never early, and not a surprise because he, err, doesn't exactly hang around when driving.
We started on the beers and indulged in some drunken rallying.
I think around 5am while it was his turn to race around the Norwegian countryside, I remembered AoC would have unlocked for that day. Perfect opportunity to get in quick and score a higher position on the leaderboard.
No chance, this one was a humdinger. Welcome to 2021.19.
Reading through the puzzle (even with my beer and rally addled brain), I thought how interesting this one was. Between turns on the driving rig I found myself pondering the possible solutions.
The AoC description covers the puzzle in detail obviously, but the short version is:
- You have a bunch of scanners in the ocean.
- These scanners report back to you a list of beacons they can detect within their sensor range.
- The scanners report back the beacon locations relative to the scanner's own position.
- The scanner doesn't know which way it is facing (a bit like me that evening to be honest.)
That last point means you could have two scanners, in the exact same location, detecting exactly the same beacons, but reporting back two entirely different sets of coordinates.
What followed was a mixture of drinking, rallying and me and my mate using the right hand rule a lot.
Then we passed out.
