AoC_2020/src/day12.rs

use aoc_runner_derive::{aoc, aoc_generator};

#[derive(Debug)]
pub enum Direction {
    North,
    East,
    South,
    West,
}

impl Direction {
    fn from_int(n: i64) -> Self {
        match n % 4 {
            0 => Self::East,
            1 => Self::South,
            2 => Self::West,
            3 => Self::North,
            _ => unreachable!(),
        }
    }
}

#[derive(Debug)]
pub enum Command {
    Direction(Direction, i64),
    Left(i64),
    Right(i64),
    Forward(i64),
}

#[derive(Debug)]
pub struct Ship {
    rot: i64,
    pos: (i64, i64),
    wp: (i64, i64),
}

impl Ship {
    fn new() -> Self {
        Self {
            rot: 0,
            pos: (0, 0),
            wp: (10, 1),
        }
    }

    fn facing(&self) -> Direction {
        Direction::from_int(self.rot)
    }

    fn cmd_p1(&mut self, cmd: &Command) {
        match cmd {
            Command::Direction(Direction::North, n) => {
                self.pos.1 += n;
            }
            Command::Direction(Direction::South, n) => {
                self.pos.1 -= n;
            }
            Command::Direction(Direction::East, n) => {
                self.pos.0 += n;
            }
            Command::Direction(Direction::West, n) => {
                self.pos.0 -= n;
            }
            Command::Left(n) => {
                self.rot -= n;
            }
            Command::Right(n) => {
                self.rot += n;
            }
            Command::Forward(n) => self.cmd_p1(&Command::Direction(self.facing(), *n)),
        }
    }

    fn cmd_p2(&mut self, cmd: &Command) {
        match cmd {
            Command::Direction(Direction::North, n) => {
                self.wp.1 += n;
            }
            Command::Direction(Direction::South, n) => {
                self.wp.1 -= n;
            }
            Command::Direction(Direction::East, n) => {
                self.wp.0 += n;
            }
            Command::Direction(Direction::West, n) => {
                self.wp.0 -= n;
            }
            Command::Right(n) => {
                let wp = self.wp;
                self.wp = match n % 4 {
                    0 => wp,
                    1 => (wp.1, -wp.0),
                    2 => (-wp.0, -wp.1),
                    3 => (-wp.1, wp.0),
                    _ => unreachable!(),
                };
            }
            Command::Left(n) => {
                let wp = self.wp;
                self.wp = match n % 4 {
                    0 => wp,
                    1 => (-wp.1, wp.0),
                    2 => (-wp.0, -wp.1),
                    3 => (wp.1, -wp.0),
                    _ => unreachable!(),
                };
            }
            Command::Forward(n) => {
                self.pos.0 += self.wp.0 * n;
                self.pos.1 += self.wp.1 * n;
            }
        }
    }
}

#[aoc_generator(day12)]
pub fn input_generator(input: &str) -> Vec<Command> {
    input
        .lines()
        .map(|l| {
            let mut chars = l.chars();
            let cmd = chars.next().unwrap();
            let num = chars.collect::<String>().parse().unwrap();
            match cmd {
                'N' => Command::Direction(Direction::North, num),
                'S' => Command::Direction(Direction::South, num),
                'E' => Command::Direction(Direction::East, num),
                'W' => Command::Direction(Direction::West, num),
                'L' if num % 90 == 0 => Command::Left((num / 90) % 4),
                'R' if num % 90 == 0 => Command::Right((num / 90) % 4),
                'F' => Command::Forward(num),
                _ => panic!("Invalid command: {}", l),
            }
        })
        .collect::<Vec<Command>>()
}

#[aoc(day12, part1)]
pub fn solve_part1(input: &[Command]) -> usize {
    let mut ship = Ship::new();
    for cmd in input {
        ship.cmd_p1(cmd);
    }
    return (ship.pos.0.abs() as usize) + (ship.pos.1.abs() as usize);
}

#[aoc(day12, part2)]
pub fn solve_part2(input: &[Command]) -> usize {
    let mut ship = Ship::new();
    for cmd in input {
        ship.cmd_p2(cmd);
    }
    return (ship.pos.0.abs() as usize) + (ship.pos.1.abs() as usize);
}