This is my attempt to solve all the Advent of Code 2021 problems in pure nix.
I wasn't trying to make efficient solutions, just efficient enough to complete and get me a successful answer. This was primarily to just play around with nix, not to code golf or do anything fancy.
In general, nix eval '.#dayX' (where 'X' is the number of the day, padded to length 2, such as
nix eval '.#day03') will display the answer to a given day.
This one is the first one where the performance is bad. Really bad.
Bad enough that you need to run it specially:
$ ulimit -s unlimited
$ nix eval '.#day05.part1'
$ nix eval '.#day05.part2'
Running the parts separately helps, and removing the stack size limit is needed for part 2.
On my computer, it takes around 4 minutes to complete. It takes more than 15GiB of memory as well.
I may come back to this one to optimize the solution further since having to increase the stack size seems far from ideal.
This is the first part where the answer needs specific formatting.
Using --raw or --json | jq '.' -r will provide correct formatting. For example:
$ nix eval '.#day13.part2' --raw
Also, you need a fixed width terminal, but that's kinda a given.
This one takes on the order of 8 minutes on my machine, with ~40GiB of memory usage.
This one's another real slow one. It takes 13 minutes per part on my machine.
Slow. 8 minutes on my machine.
We're on a roll with slow implementations that run just quick enough to complete. 5 minutes on my machine, and it took ~60GiB of RSS.
From here on, I'll stop noting slow runtimes unless they're really big.
Each part takes over 30 minutes to run. Really big runtime.