aoc22/src/day12/main.rs

use std::collections::{HashMap, VecDeque};
use base::read_file;

#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
struct Pos(usize, usize);

impl Pos {
    fn left(&self) -> Self { Pos(self.0 - 1, self.1) }
    fn right(&self) -> Self { Pos(self.0 + 1, self.1) }
    fn up(&self) -> Self { Pos(self.0, self.1 - 1) }
    fn down(&self) -> Self { Pos(self.0, self.1 + 1) }

    fn getHeight(&self, tiles: &Vec<Vec<u8>>) -> u8 {
        return tiles[self.1][self.0];
    }
}

fn get_positions(tiles: &Vec<Vec<u8>>, pos: Pos, width: usize, height: usize) -> Vec<Pos> {
    let current_height = pos.getHeight(&tiles);
    let mut positions = vec![];
    if pos.0 > 0 {
        positions.push(pos.left())
    }
    if pos.1 > 0 {
        positions.push(pos.up());
    }
    if pos.0 < width - 1 {
        positions.push(pos.right());
    }
    if pos.1 < height - 1 {
        positions.push(pos.down());
    }

    let mut i = 0;
    while i < positions.len() {
        if positions[i].getHeight(&tiles) > current_height + 1 {
            let _ = positions.remove(i);
        } else {
            i += 1;
        }
    }

    positions
}

fn pathfinding_dijkstra(start: Pos, end: Pos, tiles: &Vec<Vec<u8>>) -> Option<u32> {
    let height = tiles.len();
    let width = tiles[0].len();
    let mut discovered = HashMap::<Pos, Option<Pos>>::new();
    discovered.insert(start, None);
    let mut to_search = VecDeque::new();
    to_search.push_front(start);

    while !to_search.is_empty() {
        if let Some(u) = to_search.pop_back() {
            for position in get_positions(tiles, u, width, height) {
                if let None = discovered.get(&position) {
                    discovered.insert(position, Some(u));
                    to_search.push_front(position);
                }
            }
        }
    }
    let mut position = end;
    let mut counter = 0;
    loop {
        if let Some(pre) = discovered.get(&position) {
            if let Some(pos) = pre {
                position = *pos;
                counter += 1;
            } else {
                break;
            }
        } else {
            return None;
        }
    }

    Some(counter)
}

fn main() {
    let lines = read_file("day12.txt");

    let mut start = None;
    let mut end = None;
    let mut tiles = vec![];
    let mut zero_height_tiles = vec![];

    for (y, line) in lines.iter().enumerate() {
        tiles.push(vec![]);
        for (x, c) in line.bytes().enumerate() {
            match c {
                83 => {
                    let pos = Pos(x, y);
                    start = Some(pos);
                    zero_height_tiles.push(pos);
                    tiles[y].push(0);
                }
                69 => {
                    end = Some(Pos(x, y));
                    tiles[y].push(25);
                }
                _ => {
                    let height = c - 'a' as u8;
                    tiles[y].push(height);
                    if height == 0 {
                        zero_height_tiles.push(Pos(x, y));
                    }
                }
            }
        }
    }

    println!("Task 1: {}", pathfinding_dijkstra(start.unwrap(), end.unwrap(), &tiles).unwrap());

    let task2 = zero_height_tiles.iter().filter_map(|start| pathfinding_dijkstra(*start, end.unwrap(), &tiles)).min().unwrap();

    println!("Task 2: {}", task2);
}