day3.rs

static INPUT: &str = include_str!("../inputs/3.txt");

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
struct Slope {
    // positive x is right
    pub x: u8,
    // positive y is down
    pub y: u8,
}

impl Default for Slope {
    fn default() -> Self {
        Self { x: 1, y: 1 }
    }
}

impl From<(u8, u8)> for Slope {
    fn from((x, y): (u8, u8)) -> Self {
        Self { x, y }
    }
}

impl From<u8> for Slope {
    fn from(x: u8) -> Self {
        Self {
            x,
            ..Default::default()
        }
    }
}

fn count_trees(slope: impl Into<Slope>) -> usize {
    let slope = slope.into();
    INPUT
        .lines()
        .step_by(slope.y as usize)
        .enumerate()
        .filter(|(d, s)| s.chars().cycle().nth(d * slope.x as usize) == Some('#'))
        .count()
}

fn main() {
    println!("{}", count_trees(3));
    let part_two = [(1, 1), (3, 1), (5, 1), (7, 1), (1_u8, 2_u8)]
        .iter()
        .copied()
        .map(count_trees)
        .product::<usize>();
    println!("{}", part_two);
}