aoc2023/16/src/main.rs

use std::fmt::Display;
use std::fs::File;
use std::io::{BufRead, BufReader, Lines};
use std::iter::repeat;
use std::time::Instant;

// BOILERPLATE
type InputIter = Lines<BufReader<File>>;

fn get_input() -> InputIter {
    let f = File::open("input").unwrap();
    let br = BufReader::new(f);
    br.lines()
}

fn main() {
    let start = Instant::now();
    let ans1 = problem1(get_input());
    let duration = start.elapsed();
    println!("Problem 1 solution: {} [{}s]", ans1, duration.as_secs_f64());

    let start = Instant::now();
    let ans2 = problem2(get_input());
    let duration = start.elapsed();
    println!("Problem 2 solution: {} [{}s]", ans2, duration.as_secs_f64());
}

// PARSE

enum Interaction {
    One(FromDirection),
    Two((FromDirection, FromDirection)),
}

#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
enum FromDirection {
    Left = 0,
    Above = 1,
    Right = 2,
    Below = 3,
}

impl FromDirection {
    fn mask(&self) -> u8 {
        1 << *self as u8
    }
    // return the new pos for a ray that will be from the direction.
    // a ray 'from' left 'goes' right
    fn goes_pos(&self, pos: (i64, i64)) -> (i64, i64) {
        match self {
            Self::Left => (pos.0 + 1, pos.1),
            Self::Right => (pos.0 - 1, pos.1),
            Self::Above => (pos.0, pos.1 + 1),
            Self::Below => (pos.0, pos.1 - 1),
        }
    }
    fn reflect_ne(&self) -> Self {
        match self {
            Self::Left => Self::Below,
            Self::Right => Self::Above,
            Self::Above => Self::Right,
            Self::Below => Self::Left,
        }
    }
    fn opposite(&self) -> FromDirection {
        match self {
            Self::Left => Self::Right,
            Self::Right => Self::Left,
            Self::Above => Self::Below,
            Self::Below => Self::Above,
        }
    }
    fn reflect_se(&self) -> FromDirection {
        self.reflect_ne().opposite()
    }
    fn interact(&self, tile: char) -> Interaction {
        match tile {
            '.' => Interaction::One(*self),
            '/' => Interaction::One(self.reflect_ne()),
            '\\' => Interaction::One(self.reflect_se()),
            '|' => match self {
                FromDirection::Above | FromDirection::Below => Interaction::One(*self),
                FromDirection::Left | FromDirection::Right => {
                    Interaction::Two((FromDirection::Above, FromDirection::Below))
                }
            },
            '-' => match self {
                FromDirection::Left | FromDirection::Right => Interaction::One(*self),
                FromDirection::Above | FromDirection::Below => {
                    Interaction::Two((FromDirection::Left, FromDirection::Right))
                }
            },
            c => unimplemented!("invalid tile {}", c),
        }
    }
}

impl Display for FromDirection {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Above => f.write_str("above"),
            Self::Below => f.write_str("below"),
            Self::Left => f.write_str("left"),
            Self::Right => f.write_str("right"),
        }
    }
}

struct Contraption {
    tiles: Vec<Vec<char>>,
}

struct VisitState {
    visited_from: Vec<Vec<u8>>,
}

impl VisitState {
    fn visit(&mut self, pos: (i64, i64), dir: FromDirection) -> bool {
        let pos_state = &mut self.visited_from[pos.1 as usize][pos.0 as usize];
        if *pos_state & dir.mask() > 0 {
            false
        } else {
            *pos_state |= dir.mask();
            true
        }
    }
    fn score(&self) -> u64 {
        self.visited_from
            .iter()
            .flatten()
            .filter(|c| **c != 0)
            .count() as u64
    }
    #[allow(dead_code)]
    fn dump(&self) {
        println!("Score {}:", self.score());
        for line in &self.visited_from {
            println!(
                "  {}",
                String::from_iter(line.iter().map(|b| if *b == 0 { '.' } else { '#' }))
            );
        }
    }
}

impl Contraption {
    fn height(&self) -> i64 {
        self.tiles.len() as i64
    }
    fn width(&self) -> i64 {
        self.tiles[0].len() as i64
    }
    fn cast_ray<'a>(&'a mut self, pos: (i64, i64), dir: FromDirection) -> VisitState {
        let mut state = self.empty_state();
        self.cast_ray_inner(&mut state, pos, dir);
        state
    }
    fn cast_ray_inner<'a>(
        &'a mut self,
        state: &'a mut VisitState,
        pos: (i64, i64),
        dir: FromDirection,
    ) {
        if pos.0 >= 0
            && pos.1 >= 0
            && pos.0 < self.width()
            && pos.1 < self.height()
            && state.visit(pos, dir)
        {
            match dir.interact(self.tiles[pos.1 as usize][pos.0 as usize]) {
                Interaction::One(dir) => self.cast_ray_inner(state, dir.goes_pos(pos), dir),
                Interaction::Two((dir1, dir2)) => {
                    self.cast_ray_inner(state, dir1.goes_pos(pos), dir1);
                    self.cast_ray_inner(state, dir2.goes_pos(pos), dir2);
                }
            };
        }
    }
    fn empty_state(&self) -> VisitState {
        let mut visited_from = Vec::new();
        for _ in 0..self.height() {
            visited_from.push(Vec::from_iter(repeat(0).take(self.width() as usize)));
        }
        VisitState { visited_from }
    }
}

impl<T: BufRead> From<Lines<T>> for Contraption {
    fn from(lines: Lines<T>) -> Self {
        let mut tiles = Vec::new();
        for line in lines {
            tiles.push(line.unwrap().chars().map(|c| c.into()).collect());
        }
        Contraption { tiles }
    }
}

// PROBLEM 1 solution

fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
    let mut contraption = Contraption::from(input);

    contraption.cast_ray((0, 0), FromDirection::Left).score()
}

// PROBLEM 2 solution
fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
    let mut contraption = Contraption::from(input);

    let rows_max = (0..contraption.height()).fold(0, |max_tiles, y| {
        std::cmp::max(
            max_tiles,
            std::cmp::max(
                contraption.cast_ray((0, y), FromDirection::Left).score(),
                contraption
                    .cast_ray((contraption.width() - 1, y), FromDirection::Right)
                    .score(),
            ),
        )
    });

    let cols_max = (0..contraption.width()).fold(0, |max_tiles, x| {
        std::cmp::max(
            max_tiles,
            std::cmp::max(
                contraption.cast_ray((x, 0), FromDirection::Above).score(),
                contraption
                    .cast_ray((x, contraption.height() - 1), FromDirection::Below)
                    .score(),
            ),
        )
    });

    std::cmp::max(rows_max, cols_max)
}

#[cfg(test)]
mod tests {
    use crate::*;
    use std::io::Cursor;

    const EXAMPLE: &str = &r".|...\....
|.-.\.....
.....|-...
........|.
..........
.........\
..../.\\..
.-.-/..|..
.|....-|.\
..//.|....";

    #[test]
    fn problem1_example() {
        let c = Cursor::new(EXAMPLE);
        assert_eq!(problem1(c.lines()), 46);
    }

    #[test]
    fn problem2_example() {
        let c = Cursor::new(EXAMPLE);
        assert_eq!(problem2(c.lines()), 51);
    }
}