pub fn part_two(input: &str) -> Option<usize> {
    let mut lines = input.lines();
    let steps: Vec<char> = lines.next()?.chars().collect();

    lines.next()?;

    type Node = (char, char, char);
    let moves: HashMap<Node, (Node, Node)> = lines
        .map(|line| {
            let l: Vec<char> = line.chars().collect();
            ((l[0], l[1], l[2]), ((l[7], l[8], l[9]), (l[12], l[13], l[14])))
        })
        .collect();

    Some(
        moves
            .keys()
            .filter(|pos| pos.2 == 'A')
            .map(|pos: &Node| {
                steps
                    .iter()
                    .cycle()
                    .scan(pos, |p, &dir: &char|
                        match p.2 {
                            'Z' => None,
                            _ => Some(*p = match dir { 'L' => &moves[p].0, _ => &moves[p].1})
                        }
                    )
                    .count()
            })
            .fold(1, |a, b| a * b / gcd::binary_usize(a, b)),
    )
}