aoc2024/src/days/d6.rs

#![allow(non_upper_case_globals)]
use crate::prelude::*;

pub type I = Vec<Vec<char>>;
pub type O = usize;

fn _parse (data: &str) -> I {
    data.lines().map(|line| line.chars().collect()).collect()
}

fn _traverse (data: &I) -> S<(usize, usize)> {
    let (mut sy, mut sx) = data.iter().enumerate().find_map(|(y, row)| row.iter().position(|e| *e == '^').map(|x| (y, x))).unwrap();

    let rows = data.len();
    let cols = data[0].len();

    let mut s: S<(usize, usize)> = S::new();
    const dirs: [(isize, isize); 4] = [(-1, 0), (0, 1), (1, 0), (0, -1)];
    let mut dir = 0;

    loop {

        let (dy, dx) = dirs[dir];
        let ny = sy.checked_add_signed(dy);
        let nx = sx.checked_add_signed(dx);

        match (ny, nx) {
            (Some(ny), Some(nx)) if ny < rows && nx < cols => {
                if data[ny][nx] == '#' {
                    dir = (dir + 1) % 4;
                } else {
                    s.insert((ny, nx));
                    sy = ny;
                    sx = nx;
                }
            },
            _ => break,
        }

    }

    s
}

fn _silver (data: I) -> O {
    let ans = _traverse(&data);
    ans.len()
}

fn _gold (mut data: I) -> O {
    let path = _traverse(&data);
    let (sy, sx) = data.iter().enumerate().find_map(|(y, row)| row.iter().position(|e| *e == '^').map(|x| (y, x))).unwrap();
    data[sy][sx] = '.';

    let rows = data.len();
    let cols = data[0].len();

    const dirs: [(isize, isize); 4] = [(-1, 0), (0, 1), (1, 0), (0, -1)];

    let mut loops = 0;

    'outer : for (cy, cx) in path {
        if cy == sy && cx == sx { continue; }
        if data[cy][cx] == '.' {
            data[cy][cx] = '#';

            let mut y = sy;
            let mut x = sx;

            let mut s: S<((usize, usize), usize)> = S::new();
            let mut dir = 0;

            'inner : loop {
                let (dy, dx) = dirs[dir];

                if s.contains(&((y, x), dir)) {
                    loops += 1;
                    data[cy][cx] = '.';
                    continue 'outer;
                }
                s.insert(((y, x), dir));

                let ny = y.checked_add_signed(dy);
                let nx = x.checked_add_signed(dx);

                match (ny, nx) {
                    (Some(ny), Some(nx)) if ny < rows && nx < cols => {
                        if data[ny][nx] == '#' {
                            dir = (dir + 1) % 4;
                        } else {
                            y = ny;
                            x = nx;
                        }
                    },
                    _ => break 'inner,
                }

            }

            data[cy][cx] = '.';
        }
    }

    loops
}

#[cfg(test)]
mod test {
    use super::*;

    fn read () -> I {
        let data = inc!(6);
        _parse(data)
    }

    #[test]
    fn silver () {
        let data = read();
        let ans = _silver(data);

        assert_eq!(ans, 4967)
    }

    #[test]
    fn gold () {
        let data = read();
        let ans = _gold(data);

        assert_eq!(ans, 1789)
    }
}