advent_of_code VS adventofcode

Caution: the method I used is not recommended. Use at your own risk, know what you're doing, and have plenty of backups, etc. That said, here are my notes.

Once I figured out how to elegantly move the tail using signum() in part 2 it became so much cleaner. Full code is on GitHub, but here's the core of it:

Group the fish by their timer, which can be anything from 0 to 8. The neat part is the rotate_left to decrease the timers of each group. Fish with timer 0 will automatically end up at timer 8, and so the only thing left to do is adding another copy with timer 6. Core function: rust fn multiply(timers: Vec, generations: usize) -> usize { // Index equals timer value, so index 0 contains the count of fish with timer 0 let mut counts_by_timer = vec![0usize; 9]; timers.into_iter().for_each(|f| { counts_by_timer[f] += 1; }); for _ in 0..generations { // A left rotation represents the timer (=index) decreasing by 1. // The fish with timer 0 will not only produce new fish with timer 8, // but also reset their timer to 6 let count_of_fish_with_timer_0 = counts_by_timer[0]; counts_by_timer.rotate_left(1); counts_by_timer[6] += count_of_fish_with_timer_0; // == counts_by_timer[8] } counts_by_timer.into_iter().sum() } Full code at Github

Part one went fairly fast, but spent quite some time on getting part two right. I settled on the approach of just iterating over the grid and using a boolean to see if I had to count elements or not. However, I had some issues figuring out when to swap, this post by /u/rogual helped me figure it out. After that I lost quite some time on an error that only occurred with my input, not with the example input. It turned out that my loop (which I take form my p1 solution) didn't include the start node, which caused all sorts of counting issues.

[Language: Elixir] https://github.com/mathsaey/adventofcode/blob/master/lib/2023/4.ex