advent/2021/src/day20.rs

use advent::prelude::*;
use aoc_runner_derive::aoc;

struct Image(HashSet<(isize, isize)>);

impl Image {
    fn new(input: &str) -> Image {
        let rows: Vec<_> = input.lines().collect();
        let width = rows[0].len();
        Image(
            rows.iter()
                .flat_map(|row| row.as_bytes().iter())
                .enumerate()
                .filter(|(_i, b)| *b == &b'#')
                .map(|(i, _b)| ((i % width) as isize, (i / width) as isize))
                .collect(),
        )
    }
    fn lookup(&self, x: isize, y: isize, algo: &[bool]) -> usize {
        assert_eq!(algo.len(), 512);
        let mut idx = 0;
        for y_off in -1..=1 {
            for x_off in -1..=1 {
                idx <<= 1;
                let x_idx = x + x_off;
                let y_idx = y + y_off;
                idx |= if self.0.contains(&(x_idx, y_idx)) {
                    1
                } else {
                    0
                };
            }
        }
        idx
    }
    fn extents(&self) -> (isize, isize, isize, isize) {
        self.0.iter().fold(
            (isize::MAX, isize::MIN, isize::MAX, isize::MIN),
            |(min_x, max_x, min_y, max_y), (x, y)| {
                (min_x.min(*x), max_x.max(*x), min_y.min(*y), max_y.max(*y))
            },
        )
    }

    fn enhance(&self, algo: &[bool]) -> Image {
        let (min_x, max_x, min_y, max_y) = self.extents();
        let mut new_im = HashSet::new();
        for y in min_y - 10..=max_y + 10 {
            for x in min_x - 10..=max_x + 10 {
                let idx = self.lookup(x, y, algo);
                if algo[idx] {
                    new_im.insert((x, y));
                }
            }
        }
        Image(new_im)
    }

    fn lights(&self) -> usize {
        self.0.len()
    }
    fn crop(&self, min_x: isize, max_x: isize, min_y: isize, max_y: isize) -> Image {
        let x_rng = min_x..=max_x;
        let y_rng = min_y..=max_y;
        Image(
            self.0
                .iter()
                .filter(|(x, y)| x_rng.contains(x) && y_rng.contains(y))
                .cloned()
                .collect(),
        )
    }
}

impl Debug for Image {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
        let (min_x, max_x, min_y, max_y) = self.extents();
        writeln!(f, "({}..{})x({}..{})", min_x, max_x, min_y, max_y)?;
        for y in min_y..=max_y {
            for x in min_x..=max_x {
                if self.0.contains(&(x, y)) {
                    write!(f, "#")?;
                } else {
                    write!(f, ".")?;
                }
            }
            writeln!(f)?;
        }
        Ok(())
    }
}

#[aoc(day20, part1)]
fn part1(input: &str) -> Result<usize> {
    let (algo, im) = input.split_once("\n\n").unwrap();
    let im = Image::new(im);
    let algo: Vec<bool> = algo.as_bytes().iter().map(|c| c == &b'#').collect();

    let (min_x, max_x, min_y, max_y) = im.extents();

    dbg!(&im, im.lights());
    let im = im.enhance(&algo);
    dbg!(&im, im.lights());
    let im = im.enhance(&algo);
    dbg!(&im, im.lights());
    let im = im.crop(min_x - 2, max_x + 2, min_y - 2, max_y + 2);
    dbg!(&im, im.lights());
    let answer = im.lights();
    assert!(answer < 5285);
    Ok(answer)
}

/*
#[aoc(day20, part2)]
fn part2(input: &str) -> Result<usize> {
todo!("part2");
Ok(0)
}
*/

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

    #[test]
    fn lookup() -> Result<()> {
        let input = r#"
..#.#..#####.#.#.#.###.##.....###.##.#..###.####..#####..#....#..#..##..###..######.###...####..#..#####..##..#.#####...##.#.#..#.##..#.#......#.###.######.###.####...#.##.##..#..#..#####.....#.#....###..#.##......#.....#..#..#..##..#...##.######.####.####.#.#...#.......#..#.#.#...####.##.#......#..#...##.#.##..#...##.#.##..###.#......#.#.......#.#.#.####.###.##...#.....####.#..#..#.##.#....##..#.####....##...##..#...#......#.#.......#.......##..####..#...#.#.#...##..#.#..###..#####........#..####......#..#

#..#.
#....
##..#
..#..
..###
"#
.trim();
        let (algo, im) = input.split_once("\n\n").unwrap();
        let im = Image::new(im);
        let algo: Vec<bool> = algo.as_bytes().iter().map(|c| c == &b'#').collect();
        assert_eq!(im.lookup(2, 2, &algo), 34);
        Ok(())
    }

    #[test]
    fn test_part1() -> Result<()> {
        let input = r#"
..#.#..#####.#.#.#.###.##.....###.##.#..###.####..#####..#....#..#..##..###..######.###...####..#..#####..##..#.#####...##.#.#..#.##..#.#......#.###.######.###.####...#.##.##..#..#..#####.....#.#....###..#.##......#.....#..#..#..##..#...##.######.####.####.#.#...#.......#..#.#.#...####.##.#......#..#...##.#.##..#...##.#.##..###.#......#.#.......#.#.#.####.###.##...#.....####.#..#..#.##.#....##..#.####....##...##..#...#......#.#.......#.......##..####..#...#.#.#...##..#.#..###..#####........#..####......#..#

#..#.
#....
##..#
..#..
..###
"#
.trim();
        assert_eq!(part1(input)?, 35);
        Ok(())
    }

    /*
    #[test]
    fn test_part2()->Result<()> {
    let input = r#"
    "#
    .trim();
    assert_eq!(part2(input)?, usize::MAX);
    Ok(())
    }
    */
}