2020: day12: part 2

This commit is contained in:
Antoine Martin 2020-12-12 15:39:09 +01:00
parent 1be8717564
commit e19ca07c6b

View file

@ -8,6 +8,7 @@ pub fn run() -> aoc::Result<String> {
let mut res = String::with_capacity(128);
writeln!(res, "part 1: {}", part1(INPUT)?)?;
writeln!(res, "part 2: {}", part2(INPUT)?)?;
Ok(res)
}
@ -27,6 +28,21 @@ fn part1(input: &str) -> aoc::Result<i64> {
Ok(ship.manhattan_distance())
}
fn part2(input: &str) -> aoc::Result<i64> {
let actions: Vec<Action> = input
.lines()
.map(|line| line.parse())
.collect::<aoc::Result<_>>()?;
let mut ship = Ship::new();
for a in actions {
ship.process_with_waypoint(a);
}
Ok(ship.manhattan_distance())
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Direction {
North,
@ -92,6 +108,8 @@ struct Ship {
direction: Direction,
x: i64,
y: i64,
waypoint: Waypoint,
}
impl Ship {
@ -100,6 +118,7 @@ impl Ship {
direction: Direction::East,
x: 0,
y: 0,
waypoint: Waypoint::new(),
}
}
@ -156,18 +175,90 @@ impl Ship {
}
}
fn process_with_waypoint(&mut self, action: Action) {
match action.kind {
ActionKind::Move(dir) => match dir {
Direction::North => self.waypoint.y -= action.arg as i64,
Direction::South => self.waypoint.y += action.arg as i64,
Direction::West => self.waypoint.x -= action.arg as i64,
Direction::East => self.waypoint.x += action.arg as i64,
},
ActionKind::Left => {
debug_assert!(action.arg % 90 == 0, "only right angles are supported");
let quarters = (action.arg / 90) as usize % 4;
for _ in 0..quarters {
let x = self.waypoint.x as i64;
let y = self.waypoint.y as i64;
self.waypoint.x = y;
self.waypoint.y = -x;
}
}
ActionKind::Right => {
debug_assert!(action.arg % 90 == 0, "only right angles are supported");
let quarters = (action.arg / 90) as usize % 4;
for _ in 0..quarters {
let x = self.waypoint.x as i64;
let y = self.waypoint.y as i64;
self.waypoint.x = -y;
self.waypoint.y = x;
}
}
ActionKind::Forward => {
let (west_east, north_south) = self.waypoint.as_dirs();
self.forward(west_east, self.waypoint.x.abs() as u16 * action.arg);
self.forward(north_south, self.waypoint.y.abs() as u16 * action.arg);
}
}
}
fn forward(&mut self, direction: Direction, arg: u16) {
let arg = arg as i64;
match direction {
Direction::North => self.y -= arg,
Direction::South => self.y += arg,
Direction::West => self.x -= arg,
Direction::East => self.x += arg,
Direction::North => self.y -= arg as i64,
Direction::South => self.y += arg as i64,
Direction::West => self.x -= arg as i64,
Direction::East => self.x += arg as i64,
}
}
}
#[derive(Debug, Clone)]
struct Waypoint {
x: i64,
y: i64,
}
impl Waypoint {
fn new() -> Self {
Self { x: 10, y: -1 }
}
fn as_dirs(&self) -> (Direction, Direction) {
let west_east = if self.x < 0 {
Direction::West
} else {
Direction::East
};
let north_south = if self.y < 0 {
Direction::North
} else {
Direction::South
};
(west_east, north_south)
}
}
#[cfg(test)]
mod tests {
use super::*;
@ -183,4 +274,14 @@ mod tests {
fn part1_real() {
assert_eq!(part1(INPUT).unwrap(), 1589);
}
#[test]
fn part2_provided() {
assert_eq!(part2(PROVIDED).unwrap(), 286);
}
#[test]
fn part2_real() {
assert_eq!(part2(INPUT).unwrap(), 23960);
}
}