[2022 Day 14] In Review (Regolith Reservoir)

The distress signal lead to a waterfall, and as the trope goes, there's a large hidden cave behind it. Following the signal into the cave, we find ourselves threatened by falling sand. And we have a sand physics simulation to go along with the water simulation from 2018 (Reservoir Research).

The general idea is similar... sand is falling down from a point at (500,0) like before. There are a bunch of walls that going to form obstacles to redirect the flow. The format of the input this time is different, in that the lines cover chains of walls, and it's up to us to spot which way the walls go,

As for the simulation, it's actually a bit simpler. Sand falls straight down, then diagonally to the sides, and eventually when it comes to rest, the sand piles back up. The description was very suggestive of a stack to me so that's the first solution I did... push the locations to fall down, and when things are blocked, fill and pop back up. For part 1 you need to know where go below the max Y coordinate, and for part 2 you put a floor there and run it again... it was one of the faster part 2s in this year (and I didn't gain that many positions for it, so it looks like many people were similarly well positioned for part 2). Of course, that's just the stack version of the recursive approach, so I followed up with the actual recursive version later that day. Which would be the first solution in 2022 that required turning off deep recursion warnings in Perl (it spawns about 200 of them). The recursive version is actually a little bit faster. It's certainly a lot simpler than the mutually recursive functions I did for the water in 2018.