day09.rs

use std::collections::VecDeque;

fn solve_a(players: u32, last_marble: u32) -> u32 {
    let mut score = vec![0; players as usize];
    let mut playfield = VecDeque::new();
    let mut cur_pos = 1usize;

    playfield.push_back(0);
    playfield.push_back(1);

    for i in 2..=last_marble {
        let player = ((i-1) % players) as usize;
        if i % 23 == 0 {
            let rem_pos = match cur_pos.wrapping_sub(7) {
                0 => 0,
                e if e % playfield.len() == 0 => playfield.len(),
                e if e > playfield.len() => (cur_pos + playfield.len()) - 7,
                e => e,
            };
            score[player] += i + playfield.remove(rem_pos).unwrap();
            cur_pos = rem_pos;
        } else {
            let next_pos = match cur_pos + 2 {
                e if e > playfield.len() => e % playfield.len(),
                e if e == playfield.len() => e,
                e => e,
            };
            playfield.insert(next_pos, i);
            
            cur_pos = next_pos;
        }
//        print!("[{}]", player+1);
//        for (i, p) in playfield.iter().enumerate() {
//            if i == cur_pos {
//                print!("\x1b[7m{:2}\x1b[0m ", p);
//            } else {
//                print!("{:2} ", p);
//            }
//        }
//        println!()
    }
    score.into_iter().max().unwrap()
}

fn main() {
    let players = 455;
    let last_marble_points = 71223;
    println!("A: {}", solve_a(players, last_marble_points));
    println!("B: {}", solve_a(players, last_marble_points*100));
}

#[test]
fn test_a() {
    assert_eq!(32, solve_a(9, 25));
    assert_eq!(8317, solve_a(10, 1618));
    assert_eq!(146373, solve_a(13, 7999));
    assert_eq!(2764, solve_a(17, 1104));
    assert_eq!(54718, solve_a(21, 6111));
    assert_eq!(37305, solve_a(30, 5807));
}