aoc_2024/day10/src/main.rs

use std::collections::HashSet;
use std::collections::HashMap;
use std::fs;
use std::env;
use crate::Dir::{North, South, East, West };

// nodes are (coord, direction) pairs.
// neighbors are step1+turnleft, step2+turnleft, step3+turnleft, step1+turnright, etc
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
enum Dir { North, South, East, West }

fn step(start: &Coord, d: Dir, steps: i32) -> Coord {
    match d {
        North => (start.0, start.1 - steps),
        South => (start.0, start.1 + steps),
        East => (start.0 + steps, start.1),
        West => (start.0 - steps, start.1),
    }
}

type Coord = (i32, i32);

fn main() {
    println!("Hello, AoC day 04!");

    let args: Vec<String> = env::args().collect();
    if args.len() != 2 {
        println!("wrong number of arguments!");
        std::process::exit(1);
    }

    let file_path = &args[1];

    let contents = fs::read_to_string(file_path).expect("Should have been able to read the file");
    let mut grid: HashMap<Coord, i8> = HashMap::new();
    let mut trailheads: HashSet<Coord> = HashSet::new();

    let mut x;
    // build our grid!
    let mut y = 0;
    for line in contents.lines() {
        x = 0;
        for c in line.chars() {
            let num = c.to_string().parse::<i8>().unwrap();
            let coords = (x,y);
            if num == 0 {
                trailheads.insert(coords);
            }
            grid.insert(coords, num);
            x += 1;
        }
        y += 1;
    }

    let mut sum: i32 = 0;
    for head in &trailheads {
        sum += score(*head, &grid);
    }
    println!("there are {sum} points in score total");

    let mut sum: i32 = 0;
    for head in &trailheads {
        sum += rating(*head, &grid);
    }
    println!("there are {sum} points in rating total")
}

fn score(head: Coord, grid: &HashMap<Coord, i8>) -> i32 {
    let mut visited: HashSet<Coord> = HashSet::new();
    let mut front: HashSet<Coord> = HashSet::from([head]);
    let mut peaks: HashSet<Coord> = HashSet::new();

    while !front.is_empty() {
        let mut new_front: HashSet<Coord> = HashSet::new();

        for x in front.drain() {
            if grid[&x] == 9 {
                peaks.insert(x);
            }
            visited.insert(x);
            for x2 in neighbors(&x, &grid) {
                if visited.contains(&x2) { continue; }
                new_front.insert(x2);
            }
        }
        front = new_front;
    }
    return peaks.len() as i32;
}

fn rating(head: Coord, grid: &HashMap<Coord, i8>) -> i32 {
    let mut visited: HashSet<Coord> = HashSet::new();
    let mut front: Vec<Coord> = vec![head];

    let mut points = 0;
    while !front.is_empty() {
        let mut new_front: Vec<Coord> = vec![];

        for x in front.drain(..) {
            if grid[&x] == 9 {
                points += 1;
            }
            visited.insert(x);
            let x_neighbors = neighbors(&x, &grid);

            for x2 in x_neighbors {
                if visited.contains(&x2) { continue; }
                new_front.push(x2);
            }
        }
        front = new_front;
    }
    return points as i32;
}


fn neighbors(head: &Coord, grid: &HashMap<Coord, i8>) -> HashSet<Coord> {
    let height = grid[head];
    let neighbors = vec![North, South, East, West]
        .into_iter()
        .map(|x| step(head, x, 1))
        .filter(|x| grid.contains_key(&x) && grid[&x]==height+1);
    return neighbors.collect();
}