Rust

Hardest part was parsing the input, i somehow forgot how regexes work and wasted hours.

Learning how to do matrix stuff in rust was a nice detour as well.

#[cfg(test)]
mod tests {
    use nalgebra::{Matrix2, Vector2};
    use regex::Regex;

    fn play_game(ax: i128, ay: i128, bx: i128, by: i128, gx: i128, gy: i128) -> i128 {
        for a_press in 0..100 {
            let rx = gx - ax * a_press;
            let ry = gy - ay * a_press;
            if rx % bx == 0 && ry % by == 0 && rx / bx == ry / by {
                return a_press * 3 + ry / by;
            }
        }
        0
    }

    fn play_game2(ax: i128, ay: i128, bx: i128, by: i128, gx: i128, gy: i128) -> i128 {
        // m * p = g
        // p = m' * g
        // |ax bx|.|a_press| = |gx|
        // |ay by| |b_press|   |gy|
        let m = Matrix2::new(ax as f64, bx as f64, ay as f64, by as f64);
        match m.try_inverse() {
            None => return 0,
            Some(m_inv) => {
                let g = Vector2::new(gx as f64, gy as f64);
                let p = m_inv * g;
                let pa = p[0].round() as i128;
                let pb = p[1].round() as i128;
                if pa * ax + pb * bx == gx && pa * ay + pb * by == gy {
                    return pa * 3 + pb;
                }
            }
        };
        0
    }

    #[test]
    fn day13_part1_test() {
        let input = std::fs::read_to_string("src/input/day_13.txt").unwrap();
        let re = Regex::new(r"[0-9]+").unwrap();

        let games = input
            .trim()
            .split("\n\n")
            .map(|line| {
                re.captures_iter(line)
                    .map(|x| {
                        let first = x.get(0).unwrap().as_str();
                        first.parse::<i128>().unwrap()
                    })
                    .collect::<Vec<i128>>()
            })
            .collect::<Vec<Vec<i128>>>();

        let mut total = 0;
        for game in games {
            let cost = play_game2(game[0], game[1], game[2], game[3], game[4], game[5]);
            total += cost;
        }
        // 36870
        println!("{}", total);
    }

    #[test]
    fn day12_part2_test() {
        let input = std::fs::read_to_string("src/input/day_13.txt").unwrap();
        let re = Regex::new(r"[0-9]+").unwrap();

        let games = input
            .trim()
            .split("\n\n")
            .map(|line| {
                re.captures_iter(line)
                    .map(|x| {
                        let first = x.get(0).unwrap().as_str();
                        first.parse::<i128>().unwrap()
                    })
                    .collect::<Vec<i128>>()
            })
            .collect::<Vec<Vec<i128>>>();

        let mut total = 0;
        for game in games {
            let cost = play_game2(
                game[0],
                game[1],
                game[2],
                game[3],
                game[4] + 10000000000000,
                game[5] + 10000000000000,
            );
            total += cost;
        }
        println!("{}", total);
    }
}