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day12.rs
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day12.rs
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use core::panic;
use crate::Day;
pub struct Day12(Vec<Instruction>);
#[derive(Debug)]
struct Navigable {
facing: Dir,
east: isize,
north: isize,
}
#[derive(Debug)]
enum Instruction {
Move(Dir, isize),
Turn(Turn, isize),
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
enum Dir {
North,
East,
South,
West,
}
#[derive(Debug, PartialEq, Clone, Copy)]
#[repr(u8)]
enum Turn {
Left,
Forward,
Right,
}
impl Day for Day12 {
fn parse(text: &str) -> Box<Self>
where
Self: Sized,
{
Box::new(Day12(
text.lines()
.take_while(|line| !line.is_empty())
.map(Instruction::from)
.collect(),
))
}
fn solve1(&self) -> usize {
let mut ship = Navigable::ship();
for instr in &self.0 {
match *instr {
Instruction::Move(dir, amount) => ship.move_dir(dir, amount),
Instruction::Turn(turn, degree) => match turn {
Turn::Forward => ship.move_dir(ship.facing, degree),
_ => ship.turn(turn, degree),
},
}
}
manhattan_distance((0, 0), (ship.north, ship.east))
}
fn solve2(&self) -> usize {
let mut ship = Navigable::ship();
let mut waypoint = Navigable::waypoint();
for instr in &self.0 {
match *instr {
Instruction::Move(dir, amount) => waypoint.move_dir(dir, amount),
Instruction::Turn(turn, degrees) => match turn {
Turn::Forward => {
ship.north += waypoint.north * degrees;
ship.east += waypoint.east * degrees;
}
_ => {
waypoint.turn(turn, degrees);
match waypoint.facing {
Dir::North => waypoint.north = waypoint.north.abs(),
Dir::East => waypoint.east = waypoint.east.abs(),
Dir::South => waypoint.north = -waypoint.north.abs(),
Dir::West => waypoint.east = -waypoint.east.abs(),
}
}
},
}
}
// 33234 too low
manhattan_distance((0, 0), (ship.north, ship.east))
}
}
impl From<u8> for Dir {
fn from(value: u8) -> Self {
match value {
0 => Dir::North,
1 => Dir::East,
2 => Dir::South,
3 => Dir::West,
_ => panic!("Cant convert to Dir"),
}
}
}
impl From<&str> for Instruction {
fn from(value: &str) -> Self {
let amount = value[1..]
.trim_end()
.parse()
.expect("Not a parsable number");
match &value[..1] {
"N" => Instruction::Move(Dir::North, amount),
"S" => Instruction::Move(Dir::South, amount),
"E" => Instruction::Move(Dir::East, amount),
"W" => Instruction::Move(Dir::West, amount),
"F" => Instruction::Turn(Turn::Forward, amount),
"R" => Instruction::Turn(Turn::Right, amount),
"L" => Instruction::Turn(Turn::Left, amount),
_ => unreachable!("Doesnt exist"),
}
}
}
/// Ignores first argument because it must always be zero
/// It just exists as a reminder
fn manhattan_distance(_: (isize, isize), to: (isize, isize)) -> usize {
// from is always 0 in this case because ship starts at (0, 0)
to.0.unsigned_abs() + to.1.unsigned_abs()
}
impl Navigable {
fn ship() -> Self {
Navigable {
facing: Dir::East,
east: 0,
north: 0,
}
}
fn waypoint() -> Self {
Navigable {
facing: Dir::East,
east: 10,
north: 1,
}
}
fn turn(&mut self, turn: Turn, degree: isize) {
assert_ne!(Turn::Forward, turn);
let facing_num = self.facing as i8;
// Direction number (-1/0/1) to shift to
let turn_num_dir = (turn as i8) - 1;
// For every 90° do 1 step
let steps = (degree / 90) as i8;
let new_enum_num = facing_num + (steps * turn_num_dir);
let new_facing_num = new_enum_num.rem_euclid(4) as u8;
self.facing = new_facing_num.into();
}
fn move_dir(&mut self, dir: Dir, amount: isize) {
match dir {
Dir::North => self.north += amount,
Dir::East => self.east += amount,
Dir::South => self.north -= amount,
Dir::West => self.east -= amount,
}
}
}
#[cfg(test)]
mod tests {
use super::{Day12, Dir, Navigable, Turn};
use crate::Day;
const EXAMPLE: &str = include_str!("../../data/12_example.in");
#[test]
fn test_ship_turn() {
let ship_turn = |turn: Turn, degree: isize| {
// Facing East by default for ship
let mut ship = Navigable::ship();
ship.turn(turn, degree);
ship.facing
};
assert_eq!(Dir::North, ship_turn(Turn::Left, 90));
assert_eq!(Dir::West, ship_turn(Turn::Left, 180));
assert_eq!(Dir::South, ship_turn(Turn::Left, 270));
assert_eq!(Dir::East, ship_turn(Turn::Left, 360));
assert_eq!(Dir::South, ship_turn(Turn::Right, 90));
assert_eq!(Dir::West, ship_turn(Turn::Right, 180));
assert_eq!(Dir::North, ship_turn(Turn::Right, 270));
assert_eq!(Dir::East, ship_turn(Turn::Right, 360));
}
#[test]
fn test_part1() {
let day = Day12::parse(EXAMPLE);
assert_eq!(25, day.solve1());
}
#[test]
fn test_part2() {
let day = Day12::parse(EXAMPLE);
assert_eq!(286, day.solve2());
}
}