main.rs

pub fn main() {
    let input = include_bytes!("../input.txt");
    let col = input.iter().position(|&b| b == b':').unwrap();
    let sep = input.iter().position(|&b| b == b'|').unwrap();
    let mut factors = [1usize; 256];
    println!(
        "{}",
        input
            .split(|&b| b == b'\n')
            .enumerate()
            .map(|(i, game)| {
                let factor = factors[i];
                let win_seq = &game[col + 1..sep];
                let win_count = game[sep + 1..]
                    .chunks_exact(3)
                    .map(|n| &n[1..])
                    .filter(|n| win_seq.chunks_exact(3).map(|n| &n[1..]).any(|c| &c == n))
                    .count();
                (i..i + win_count).for_each(|i| factors[i + 1] += factor);
                factor * win_count + 1
            })
            .sum::<usize>()
    );
}