2
๐ช - 2023 DAY 14 SOLUTIONS -๐ช
(programming.dev)
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
this post was submitted on 14 Dec 2023
2 points (100.0% liked)
Advent Of Code
736 readers
1 users here now
An unofficial home for the advent of code community on programming.dev!
Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.
AoC 2023
Solution Threads
| M | T | W | T | F | S | S |
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | ||||
| 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| 11 | 12 | 13 | 14 | 15 | 16 | 17 |
| 18 | 19 | 20 | 21 | 22 | 23 | 24 |
| 25 |
Rules/Guidelines
- Follow the programming.dev instance rules
- Keep all content related to advent of code in some way
- If what youre posting relates to a day, put in brackets the year and then day number in front of the post title (e.g. [2023 Day 10])
- When an event is running, keep solutions in the solution megathread to avoid the community getting spammed with posts
Relevant Communities
Relevant Links
Credits
Icon base by Lorc under CC BY 3.0 with modifications to add a gradient
console.log('Hello World')
founded 1 year ago
MODERATORS
Nim
Getting caught up slowly after spending way too long on day 12. I'll be busy this weekend though, so I'll probably fall further behind.
Part 2 looked daunting at first, as I knew brute-forcing 1 billion iterations wouldn't be practical. I did some premature optimization anyway, pre-calculating north/south and east/west runs in which the round rocks would be able to travel.
At first I figured maybe the rocks would eventually reach a stable configuration, so I added a check to detect if the current iteration matches the previous one. It never triggered, so I dumped some of the grid states and it became obvious that there was a cycle occurring. I probably should have guessed this in advance. The spin cycle is effectively a pseudorandom number generator, and all PRNGs eventually cycle. Good PRNGs have a very long cycle length, but this one isn't very good.
I added a hash table, mapping the state of each iteration to the next one. Once a value is added that already exists in the table as a key, there's a complete cycle. At that point it's just a matter of walking the cycle to determine it's length, and calculating from there.