contests/advent_of_code/2022/15/src/main.rs

use nom::{
    bytes::streaming::tag,
    character::complete::{self, multispace1},
    multi::separated_list1,
    sequence::{preceded, separated_pair},
    IResult,
};
use priority_queue::PriorityQueue;
use std::collections::HashSet;

fn parse_input(input: &str) -> IResult<&str, Vec<((i32, i32), (i32, i32))>> {
    let (input, coords) = separated_list1(
        multispace1,
        preceded(
            tag("Sensor at x="),
            separated_pair(
                separated_pair(complete::i32, tag(", y="), complete::i32),
                tag(": closest beacon is at x="),
                separated_pair(complete::i32, tag(", y="), complete::i32),
            ),
        ),
    )(input)?;

    Ok((input, coords))
}

fn manhattan_dist(a: (i32, i32), b: (i32, i32)) -> i32 {
    return (a.0 - b.0).abs() + (a.1 - b.1).abs();
}

fn _fill_map(
    beacon_map: &mut HashSet<(i32, i32)>,
    sensor_coord: (i32, i32),
    beacon_coord: (i32, i32),
) {
    let dist = manhattan_dist(sensor_coord, beacon_coord);
    let (sx, sy) = sensor_coord;

    for i in 0..=dist {
        for j in 0..=i {
            beacon_map.insert((sx + i, sy + j));
            beacon_map.insert((sx - i, sy + j));
            beacon_map.insert((sx + i, sy - j));
            beacon_map.insert((sx - i, sy - j));
        }
    }
}

fn fill_line(
    beacon_line: &mut HashSet<i32>,
    sensor_coord: (i32, i32),
    beacon_coord: (i32, i32),
    test_line: i32,
) {
    let dist = manhattan_dist(sensor_coord, beacon_coord);
    let (sx, sy) = sensor_coord;

    let cross_section_len = dist - (test_line - sy).abs();
    if cross_section_len >= 0 {
        for i in 0..=cross_section_len {
            beacon_line.insert(sx + i);
            beacon_line.insert(sx - i);
        }
    }
}

#[derive(PartialEq, Eq, Hash)]
enum EventType {
    Start,
    Intersection,
    Middle,
    End,
}

#[derive(PartialEq, Eq, Hash)]
struct Event {
    coord: (i32, i32),
    t: EventType,
    line_id: u32,
}

fn main() {
    let test_y = 2000000;

    let input_text = include_str!("../input.txt");
    let (_rest, coord_list) = parse_input(input_text).unwrap();

    // Testing the parsing

    // for ((sx, sy), (bx, by)) in coord_list {
    //     println!("Sensor at x={sx}, y={sy}: closest beacon is at x={bx}, y={by}");
    // }

    // Naive method

    // let mut beacon_map = HashSet::new();

    // for (sensor, beacon) in coord_list {
    //     fill_map(&mut beacon_map, sensor, beacon);
    // }

    // let positions = beacon_map.into_iter().filter(|(_, y)| *y == test_y).count();

    // println!("Number of positions with y={test_y}: {positions}");

    // A slightly less naive approach

    let mut beacon_line = HashSet::new();

    for (sensor, beacon) in coord_list.clone() {
        fill_line(&mut beacon_line, sensor, beacon, test_y);
    }

    println!(
        "Number of positions with y={test_y}: {}",
        beacon_line.len() - 1
    );

    // Part 2
    //
    // Ik denk dat dit misschien wel met een sweep line zou moeten kunnen.
    // Je weet immers waar alle ruiten liggen en je kan die hele mik sorteren.
    // Je krijgt dan 3 event-types: start van een lijnstuk, een kruising en het einde van een lijnstuk.
    // Enige is dat je alleen in de daadwerkelijke coordinaat-range zoals in de opgave dingen wilt
    // mee laten tellen.
    const MAX_COORD: i32 = 8000000;

    let mut event_queue: PriorityQueue<Event, (i32, i32)> = PriorityQueue::new();
    let mut line_id = 0;
    for &(sensor, beacon) in coord_list.iter() {
        let sensor = (sensor.0 * 2, sensor.1 * 2);
        let beacon = (beacon.0 * 2, beacon.1 * 2);

        let dist = manhattan_dist(sensor, beacon);

        let begin = (sensor.0 + dist, sensor.1);
        let middle_1 = (sensor.0, sensor.1 - dist);
        let middle_2 = (sensor.0, sensor.1 + dist);
        let end = (sensor.0 - dist, sensor.1);

        event_queue.push(
            Event {
                coord: begin,
                t: EventType::Start,
                line_id,
            },
            begin,
        );
        event_queue.push(
            Event {
                coord: middle_1,
                t: EventType::Middle,
                line_id,
            },
            middle_1,
        );
        event_queue.push(
            Event {
                coord: middle_2,
                t: EventType::Middle,
                line_id,
            },
            middle_2,
        );
        event_queue.push(
            Event {
                coord: end,
                t: EventType::End,
                line_id,
            },
            end,
        );

        line_id += 1;
    }
}