Advent of Code 2021 - Day 6: Lanternfish

lanternfish.rs

fn breed(fish: &[u8], generations: u64) -> u64 {
    let mut lifetimes = vec![0u64; 9];

    fish.iter().for_each(|&f| lifetimes[f as usize] += 1);

    for _ in 0..generations {
        lifetimes.rotate_left(1);
        lifetimes[6] += lifetimes[8];
    }

    lifetimes.iter().sum()
}