Advent of Code 2021 - Day 17: Trick Shot

trick_shot.rs

fn main() {
    let hits = find_all_hits((128, 160, -142, -88));

    let max_height = hits.iter().map(|&(_, y)| triangle(y)).max().unwrap();
    let total_hits = hits.len();

    println!("The highest position reached was {}.", max_height);
    println!("The total number of hits was {}.", total_hits);
}

fn triangle(n: i64) -> i64 {
    (n.pow(2) + n) / 2
}

fn triangle_root(n: i64) -> i64 {
    (n as f64 * 2.0).sqrt() as i64
}

fn find_all_hits((min_x, max_x, min_y, max_y): (i64, i64, i64, i64)) -> Vec<(i64, i64)> {
    (triangle_root(min_x)..=max_x)
        .flat_map(|x| {
            (min_y..-min_y)
                .map(move |y| (x, y))
                .filter(|&v| hits_target(v, (min_x, max_x, min_y, max_y)))
        })
        .collect()
}

fn hits_target(
    (mut x_velocity, mut y_velocity): (i64, i64),
    (min_x, max_x, min_y, max_y): (i64, i64, i64, i64),
) -> bool {
    let mut x = 0;
    let mut y = 0;

    while y_velocity > 0 || y >= min_y {
        if x >= min_x && x <= max_x && y >= min_y && y <= max_y {
            return true;
        }

        x += x_velocity;
        y += y_velocity;

        x_velocity -= x_velocity.cmp(&0) as i64;
        y_velocity -= 1;
    }
    false
}