Rust code shared from the playground

playground.rs

// 25x25
const INPUT: &str = "\
#.....##.####.#.#########
.###..#..#..####.##....#.
..#########...###...####.
.##.#.##..#.#..#.#....###
...##....###..#.#..#.###.
###..#...######.####.#.#.
#..###..###..###.###.##..
.#.#.###.#.#...####..#...
##........##.####..##...#
.#.##..#.#....##.##.##..#
###......#..##.####.###.#
....#..###..#######.#...#
#####.....#.##.#..#..####
.#.###.#.###..##.#..####.
..#..##.###...#######....
.#.##.#.#.#.#...###.#.#..
##.###.#.#.###.#......#..
###..##.#...#....#..####.
.#.#.....#..#....##..#..#
#####.#.##..#...##..#....
##..#.#.#.####.#.##...##.
..#..#.#.####...#........
###.###.##.#..#.##.....#.
.##..##.##...#..#..#.#..#
#...####.#.##...#..#.#.##\
";

// 3x3
const _INPUT: &str = "\
..#
#..
...\
";

const INPUT_SIZE: usize = 25;
const SIZE: usize = 999;
const ITERATIONS: usize = 10_000_000;

#[derive(Clone, Copy, Debug)]
enum State {
    Clean,
    Weakened,
    Infected,
    Flagged,
}
use self::State::*;

fn main() {
    let mut grid = Box::new([[Clean; SIZE]; SIZE]);
    let center_offset = (SIZE - INPUT_SIZE) / 2;
    
    for (i, line) in INPUT.split('\n').enumerate() {
        for (j, c) in line.chars().enumerate() {
            grid[center_offset + i][center_offset + j] = if c == '#' {
                Infected
            } else {
                Clean
            };
        }
    }
    
    let mut pos = (0, 0);
    let mut dir = (-1, 0);
    let mut infect_count = 0;
    
    for _ in 0..ITERATIONS {
        let center = ((SIZE - 1) / 2) as isize;
        let i = (center + pos.0) as usize;
        let j = (center + pos.1) as usize;
        
        grid[i][j] = match grid[i][j] {
            Infected => {
                dir = match dir {
                    (1,  0) => (0, -1),
                    (-1, 0) => (0,  1),
                    (0,  1) => (1,  0),
                    (0, -1) => (-1, 0),
                    _ => unreachable!(),
                };
                Flagged
            }
            
            Clean => {
                dir = match dir {
                    (0, -1) => (1,  0),
                    (0,  1) => (-1, 0),
                    (1,  0) => (0,  1),
                    (-1, 0) => (0, -1),
                    _ => unreachable!(),
                };
                Weakened
            }
            
            Weakened => {
                infect_count += 1;
                Infected
            }
            
            Flagged => {
                dir = (-dir.0, -dir.1);
                Clean
            }
        };
        
        pos.0 += dir.0;
        pos.1 += dir.1;
    }
    
    println!("{}", infect_count);
}