puzzles/advent_of_code_2023/day10/main2.rs

use core::panic;
use std::{fs::read_to_string, ops};

#[derive(Clone, Copy, PartialEq, Eq, Debug)]
struct Point {
    x: isize,
    y: isize
}

impl Point {
    fn new(x: isize, y: isize) -> Point {
        Point {x, y}
    }

    fn moved(&self, dx: isize, dy: isize) -> Point {
        return Point::new(self.x + dx, self.y + dy);
    }

    fn moves(&self, instruction: u8) -> (Point, Point) {
        match instruction {
            b'|' => (self.moved(0, 1), self.moved(0, -1)),
            b'-' => (self.moved(1, 0), self.moved(-1, 0)),
            b'L' => (self.moved(0, -1), self.moved(1, 0)),
            b'J' => (self.moved(-1, 0), self.moved(0, -1)),
            b'7' => (self.moved(-1, 0), self.moved(0, 1)),
            b'F' => (self.moved(1, 0), self.moved(0, 1)),
            _ => (self.clone(), self.clone())
        }
    }

    fn get_instruction(&self, map: &Vec<&[u8]>) -> Option<u8> {
        let x = self.x as usize;
        let y = self.y as usize;
        
        if self.y < 0 || y >= map.len() {
            return None;
        }

        if self.x < 0 || x >= map[y].len() {
            return None;
        }

        Some(map[y][x])
    }
}

impl ops::Add for &Point {
    type Output = Point;

    fn add(self, rhs: &Point) -> Point {
        Point::new(self.x + rhs.x, self.y + rhs.y)
    }
}

impl ops::Add<&(isize, isize)> for &Point {
    type Output = Point;

    fn add(self, rhs: &(isize, isize)) -> Point {
        Point::new(self.x + rhs.0, self.y + rhs.1)
    }
}

fn find_start(map: &Vec<&[u8]>) -> Point {
    for ypos in 0..map.len() {
        for xpos in 0..map[ypos].len() {
            if map[ypos][xpos] == b'S' {
                return Point::new(xpos as isize, ypos as isize);
            }
        }
    }

    Point::new(0, 0)
}

fn is_connected(instruction: &Option<u8>, start: &Point, end: &Point) -> bool {
    match instruction {
        None => false,
        Some(instr) => {
            let (p1, p2) = start.moves(*instr);
            p1 == *end || p2 == *end 
        }
    }
}

fn find_connections(map: &Vec<&[u8]>, position: &Point) -> (Point, Point) {
    let mut moves: Vec<Point> = Vec::new();

    if is_connected(&position.moved(-1, 0).get_instruction(map), &position.moved(-1, 0), position) {
        moves.push(position.moved(-1, 0));
    }
    if is_connected(&position.moved(1, 0).get_instruction(map), &position.moved(1, 0), position) {
        moves.push(position.moved(1, 0));
    }
    if is_connected(&position.moved(0, -1).get_instruction(map), &position.moved(0, -1), position) {
        moves.push(position.moved(1, 0));
    }
    if is_connected(&position.moved(0, 1).get_instruction(map), &position.moved(0, 1), position) {
        moves.push(position.moved(0, 1));
    }

    if moves.len() != 2 {
        panic!("Got more then two moves :(");
    }

    (moves[0], moves[1])
}

fn write(map: &mut Vec<Vec<bool>>, pos: &Point) {
    map[pos.y as usize][pos.x as usize] = true;
}

fn step(map: &Vec<&[u8]>, distances: &mut Vec<Vec<bool>>, pos: &Point) -> Option<Point> {
    let (p1, p2) = pos.moves(pos.get_instruction(map).unwrap());

    if !distances[p1.y as usize][p1.x as usize] {
        write(distances, &p1);
        return Some(p1);
    }

    if !distances[p2.y as usize][p2.x as usize] {
        write(distances, &p2);
        return Some(p2);
    }

    None
}

fn next_state(instruction: u8, in_route: bool, inside: bool) -> bool {
        if !in_route {
            return inside;
        }

        // flip on any pipe facing north
        if b"|LJ".contains(&instruction) {
            return !inside;
        }

        return inside;
}

fn main() {
    let input = read_to_string("input.txt").unwrap();
    let map = input.lines().map(|line| { line.as_bytes() }).collect::<Vec<_>>();
    let mut route: Vec<Vec<bool>> = vec![vec![false; map[0].len()]; map.len()];

    let start = find_start(&map);
    write(&mut route, &start);

    let (mut p1, _) = find_connections(&map, &start);
    write(&mut route, &p1);

    loop {
        p1 = match step(&map, &mut route, &p1) {
            Some(next) => next,
            None => break
        }
    }

    // print_route(&route);
    let mut inner_space = 0;
    
    for (route_row, map_row) in route.iter().zip(map) {
        let mut inside = false;
        
        for (position, instruction) in route_row.iter().zip(map_row) {
            inside = next_state(*instruction, *position, inside);

            if inside && !*position {
                inner_space += 1;
            }
        }
    }

    println!("Inner space: {}", inner_space);
}