aoc 2022 day09

day09.rs

use std::collections::HashSet;

fn parse<'a>(input: &'a str) -> impl Iterator<Item = (&'a str, u32)> + 'a {
    input.split("\n").map(|line| {
        let mut split = line.split(" ");
        let dir = split.next().unwrap();
        let steps = split.next().unwrap().parse::<u32>().unwrap();
        (dir, steps)
    })
}

fn main() {
    let mut t_positions = HashSet::new();
    t_positions.insert((0, 0));

    let mut rope: Vec<(i32, i32)> = vec![(0, 0); 10];

    for (dir, n) in parse(include_str!("day09_input.txt")) {
        for _ in 0..n {
            // move head
            match dir {
                "R" => rope[0].0 += 1,
                "L" => rope[0].0 -= 1,
                "U" => rope[0].1 += 1,
                "D" => rope[0].1 -= 1,
                _ => unimplemented!(),
            }
            // move tail pieces
            for i in 1..10 {
                let h = rope[i - 1];
                let t = rope[i];

                let x_dist = h.0 - t.0;
                let y_dist = h.1 - t.1;
                if x_dist.abs() > 1 || y_dist.abs() > 1 {
                    if x_dist != 0 {
                        rope[i].0 += x_dist / x_dist.abs();
                    }
                    if y_dist != 0 {
                        rope[i].1 += y_dist / y_dist.abs();
                    }
                }
            }
            t_positions.insert(rope[9]);
        }
    }
    eprintln!("num_tail_positions: {}", t_positions.len());
}