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path: root/2021/day9/src/main.rs
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use std::collections::HashSet;
use std::env;
use std::fs::File;
use std::io::{BufRead, BufReader};

#[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
struct Point {
    x: usize,
    y: usize,
    height: u32,
}

#[derive(Debug, Clone, PartialEq, Eq)]
struct Basin {
    points: HashSet<Point>,
}

fn main() {
    let reader = open_file();

    let mut points: Vec<Vec<u32>> = Vec::new();
    let mut basins: Vec<Basin> = Vec::new();

    for line in reader.lines() {
        points.push(
            line.unwrap()
                .trim()
                .chars()
                .map(|x| x.to_digit(10).unwrap())
                .collect(),
        );
    }

    let nine = vec![9];

    let mut risk_level: u32 = 0;

    for (idx, height) in points.iter().enumerate() {
        for (ndx, num) in height.iter().enumerate() {
            let up = points
                .get(((idx as isize) - 1) as usize)
                .unwrap_or(&nine)
                .get(ndx)
                .unwrap_or(&9);

            let down = points
                .get(idx + 1)
                .unwrap_or_else(|| &nine)
                .get(ndx)
                .unwrap_or_else(|| &9);

            let left = height
                .get((ndx as isize - 1) as usize)
                .unwrap_or_else(|| &9);

            let right = height
                .get((ndx as isize + 1) as usize)
                .unwrap_or_else(|| &9);

            if num < up && num < down && num < right && num < left {
                risk_level += 1 + *num;
                basins.push(Basin {
                    points: HashSet::from_iter(vec![Point {
                        x: idx,
                        y: ndx,
                        height: *num,
                    }]),
                });
            }
        }
    }

    // TODO: fix this maybe because i hate it <20-12-21, yigit> //
    for basin in basins.iter_mut() {
        let mut stack: Vec<Point> = Vec::new();
        stack.extend(basin.points.clone().into_iter());

        while !stack.is_empty() {
            let minibasin = stack.pop().unwrap();

            let up = points
                .get(((minibasin.x as isize) - 1) as usize)
                .unwrap_or(&nine)
                .get(minibasin.y)
                .unwrap_or(&9);

            let down = match points.get(minibasin.x + 1) {
                Some(line) => line.get(minibasin.y).unwrap_or(&9),
                None => &9,
            };
            let left = match points.get(minibasin.x) {
                Some(line) => line
                    .get(((minibasin.y as isize) - 1) as usize)
                    .unwrap_or(&9),
                None => &9,
            };
            let right = match points.get(minibasin.x) {
                Some(line) => line.get(minibasin.y + 1).unwrap_or(&9),
                None => &9,
            };

            if up != &9 {
                let p = Point {
                    x: minibasin.x - 1,
                    y: minibasin.y,
                    height: *up,
                };

                if !basin.points.contains(&p) {
                    stack.push(p);
                    basin.points.insert(p);
                }
            }

            if down != &9 {
                let p = Point {
                    x: minibasin.x + 1,
                    y: minibasin.y,
                    height: *down,
                };

                if !basin.points.contains(&p) {
                    stack.push(p);
                    basin.points.insert(p);
                }
            }

            if left != &9 {
                let p = Point {
                    x: minibasin.x,
                    y: minibasin.y - 1,
                    height: *left,
                };

                if !basin.points.contains(&p) {
                    stack.push(p);
                    basin.points.insert(p);
                }
            }

            if right != &9 {
                let p = Point {
                    x: minibasin.x,
                    y: minibasin.y + 1,
                    height: *right,
                };

                if !basin.points.contains(&p) {
                    stack.push(p);
                    basin.points.insert(p);
                }
            }
        }
    }

    let mut lens: Vec<usize> = basins.iter().map(|x| x.points.len()).collect();

    lens.sort_unstable();
    lens.reverse();

    let biggest_basins: usize = lens.iter().take(3).product();

    println!("{}", biggest_basins);
    println!("{}", risk_level);
}

fn open_file() -> BufReader<File> {
    let args: Vec<String> = env::args().collect();

    if args.len() != 2 {
        eprintln!("Usage: {} <filename>", args[0]);
        std::process::exit(1);
    }

    let filename = &args[1];

    let file = File::open(filename).unwrap_or_else(|_| panic!("No such file: {}", filename));
    BufReader::new(file)
}