aoc2024/src/day12.rs

#![allow(
    clippy::cast_sign_loss,
    clippy::cast_possible_wrap,
    clippy::too_many_lines
)]
use std::collections::HashSet;

use tracing::debug;

pub fn pt1(input: &str) -> usize {
    let mut res = 0;
    let mut visited: HashSet<(usize, usize)> = HashSet::new();
    let fields = input
        .lines()
        .enumerate()
        .flat_map(|(y, line)| line.chars().enumerate().map(move |(x, c)| (c, x, y)))
        .collect::<Vec<_>>();
    for &(c, x, y) in &fields {
        if visited.contains(&(x, y)) {
            continue;
        }
        let mut current_matching: HashSet<(usize, usize)> = HashSet::new();
        current_matching.insert((x, y));
        visited.insert((x, y));
        let mut previous_matching = 0;
        let mut cur_matching = current_matching.len();
        while previous_matching != cur_matching {
            let m = current_matching.clone();
            let v = visited.clone();
            for &(_cc, cx, cy) in fields
                .iter()
                .filter(|(cc, _, _)| *cc == c)
                .filter(|(_cc, cx, cy)| !v.contains(&(*cx, *cy)))
                .filter(|&&(_cc, cx, cy)| {
                    m.iter().any(|&(mx, my)| {
                        (mx.abs_diff(cx) == 1 && my == cy) || (mx == cx && my.abs_diff(cy) == 1)
                    })
                })
            {
                current_matching.insert((cx, cy));
                visited.insert((cx, cy));
            }
            previous_matching = cur_matching;
            cur_matching = current_matching.len();
        }
        debug!("char: {c} -> current_matching = {current_matching:?}");
        let area = current_matching.len();
        let perimeter = get_perim(&current_matching);
        debug!("area: {area}, perimeter:{perimeter}");
        res += area * perimeter;
    }
    res
}
fn get_perim(current_matching: &HashSet<(usize, usize)>) -> usize {
    let mut perim = 0;
    for &(x, y) in current_matching {
        if x == 0 || !current_matching.contains(&(x - 1, y)) {
            perim += 1;
        }
        if y == 0 || !current_matching.contains(&(x, y - 1)) {
            perim += 1;
        }
        if !current_matching.contains(&(x + 1, y)) {
            perim += 1;
        }
        if !current_matching.contains(&(x, y + 1)) {
            perim += 1;
        }
    }
    perim
}

fn get_perimv2(current_matching: &HashSet<(usize, usize)>) -> usize {
    let mut perim = 0;
    for &(x, y) in current_matching {
        let left_is_empty = x == 0 || !current_matching.contains(&(x - 1, y));
        let top_is_empty = y == 0 || !current_matching.contains(&(x, y - 1));
        let right_is_empty = !current_matching.contains(&(x + 1, y));
        let bottom_is_empty = !current_matching.contains(&(x, y + 1));
        let top_left_is_empty = x == 0 || y == 0 || !current_matching.contains(&(x - 1, y - 1));
        let top_right_is_empty = y == 0 || !current_matching.contains(&(x + 1, y - 1));
        let bottom_left_is_empty = x == 0 || !current_matching.contains(&(x - 1, y + 1));
        let bottom_right_is_empty = !current_matching.contains(&(x + 1, y + 1));
        if left_is_empty && top_is_empty {
            perim += 1;
        }
        if left_is_empty && bottom_is_empty {
            perim += 1;
        }
        if right_is_empty && top_is_empty {
            perim += 1;
        }
        if right_is_empty && bottom_is_empty {
            perim += 1;
        }
        if !top_is_empty && top_left_is_empty && !left_is_empty {
            perim += 1;
        }
        if !bottom_is_empty && bottom_left_is_empty && !left_is_empty {
            perim += 1;
        }
        if top_right_is_empty && !top_is_empty && !right_is_empty {
            perim += 1;
        }
        if bottom_right_is_empty && !bottom_is_empty && !right_is_empty {
            perim += 1;
        }
    }
    perim
}

pub fn pt2(input: &str) -> usize {
    let mut res = 0;
    let mut visited: HashSet<(usize, usize)> = HashSet::new();
    let fields = input
        .lines()
        .enumerate()
        .flat_map(|(y, line)| line.chars().enumerate().map(move |(x, c)| (c, x, y)))
        .collect::<Vec<_>>();
    for &(c, x, y) in &fields {
        if visited.contains(&(x, y)) {
            continue;
        }
        let mut current_matching: HashSet<(usize, usize)> = HashSet::new();
        current_matching.insert((x, y));
        visited.insert((x, y));
        let mut previous_matching = 0;
        let mut cur_matching = current_matching.len();
        while previous_matching != cur_matching {
            let m = current_matching.clone();
            let v = visited.clone();
            for &(_cc, cx, cy) in fields
                .iter()
                .filter(|(cc, _, _)| *cc == c)
                .filter(|(_cc, cx, cy)| !v.contains(&(*cx, *cy)))
                .filter(|&&(_cc, cx, cy)| {
                    m.iter().any(|&(mx, my)| {
                        (mx.abs_diff(cx) == 1 && my == cy) || (mx == cx && my.abs_diff(cy) == 1)
                    })
                })
            {
                current_matching.insert((cx, cy));
                visited.insert((cx, cy));
            }
            previous_matching = cur_matching;
            cur_matching = current_matching.len();
        }
        debug!("char: {c} -> current_matching = {current_matching:?}");
        let area = current_matching.len();
        let perimeter = get_perimv2(&current_matching);
        debug!("area: {area}, perimeter:{perimeter}");
        res += area * perimeter;
    }
    res
}

#[cfg(test)]
mod tests {
    use tracing_test::traced_test;

    use super::{pt1, pt2};
    use std::fs::read_to_string;

    #[traced_test]
    #[test]
    pub fn test_pt1() {
        let input =
            read_to_string("./inputs/day12/example.txt").expect("Missing example.txt for day12");
        assert_eq!(pt1(&input), 1930)
    }

    #[traced_test]
    #[test]
    pub fn test_pt1_2() {
        let input = read_to_string("./inputs/day12/example_2.txt")
            .expect("Missing example_2.txt for day12");
        assert_eq!(pt1(&input), 772)
    }

    #[traced_test]
    #[test]
    pub fn test_pt2() {
        let input =
            read_to_string("./inputs/day12/example.txt").expect("Missing example.txt for day12");

        assert_eq!(pt2(&input), 1206)
    }
}