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use std::collections::HashMap;
static DAY: u8 = 16;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", energized_tiles(&input));
println!("{DAY}b: {}", 0);
}
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
enum Direction {
Up,
Down,
Left,
Right,
}
enum Mirror {
Backward,
Forward,
}
impl Mirror {
fn next_direction(&self, direction: Direction) -> Direction {
match self {
Mirror::Backward => match direction {
Direction::Up => Direction::Left,
Direction::Down => Direction::Right,
Direction::Left => Direction::Up,
Direction::Right => Direction::Down,
},
Mirror::Forward => match direction {
Direction::Up => Direction::Right,
Direction::Down => Direction::Left,
Direction::Left => Direction::Down,
Direction::Right => Direction::Up,
},
}
}
}
enum Splitter {
Horizontal,
Vertical,
}
impl Splitter {
fn new_directions(&self, direction: Direction) -> Vec<Direction> {
let mut directions = Vec::new();
match self {
Splitter::Horizontal => match direction {
Direction::Up => { directions.push(Direction::Left); directions.push(Direction::Right); },
Direction::Down => { directions.push(Direction::Left); directions.push(Direction::Right); },
Direction::Left => { directions.push(direction); },
Direction::Right => { directions.push(direction); },
},
Splitter::Vertical => match direction {
Direction::Up => { directions.push(direction); },
Direction::Down => { directions.push(direction); },
Direction::Left => { directions.push(Direction::Up); directions.push(Direction::Down); },
Direction::Right => { directions.push(Direction::Up); directions.push(Direction::Down); },
},
}
directions
}
}
enum Object {
Mirror(Mirror),
Splitter(Splitter),
}
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
struct Beam {
pos: Position,
direction: Direction,
}
impl Object {
fn from(c: char) -> Option<Object> {
match c {
'\\' => Some(Object::Mirror(Mirror::Backward)),
'/' => Some(Object::Mirror(Mirror::Forward)),
'-' => Some(Object::Splitter(Splitter::Horizontal)),
'|' => Some(Object::Splitter(Splitter::Vertical)),
_ => None,
}
}
}
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
struct Position {
x: isize,
y: isize,
}
impl Position {
fn next_pos(&self, direction: Direction) -> Position {
match direction {
Direction::Up => Position { x: self.x, y: self.y - 1 },
Direction::Down => Position { x: self.x, y: self.y + 1 },
Direction::Left => Position { x: self.x - 1, y: self.y },
Direction::Right => Position { x: self.x + 1, y: self.y },
}
}
}
struct Map {
map: HashMap<Position, Object>,
energized: HashMap<Position, Vec<Direction>>,
width: isize,
height: isize,
}
impl Map {
fn new(input: &[String]) -> Map {
let mut map = HashMap::new();
for (y, line) in input.iter().enumerate() {
for (x, c) in line.chars().enumerate() {
let pos = Position { x: x as isize, y: y as isize };
if let Some(obj) = Object::from(c) {
map.insert(pos, obj);
}
}
}
Map {
map,
energized: HashMap::new(),
width: input[0].len() as isize,
height: input.len() as isize,
}
}
fn outside_map(&self, pos: Position) -> bool {
pos.x < 0 || pos.x >= self.width || pos.y < 0 || pos.y >= self.height
}
fn energize(&mut self, beam: Beam) {
let mut beams = Vec::from([beam]);
while !beams.is_empty() {
let mut beam_heads = Vec::new();
for beam in beams {
if self.outside_map(beam.pos) {
continue;
}
let energized = self.energized.entry(beam.pos).or_default();
if energized.contains(&beam.direction) {
/* identical beam already exists; current beam is part of a loop */
continue;
} else {
energized.push(beam.direction);
}
let mut beam = beam;
if let Some(obj) = self.map.get(&beam.pos) {
match obj {
Object::Mirror(mirror) => {
beam.direction = mirror.next_direction(beam.direction);
beam.pos = beam.pos.next_pos(beam.direction);
beam_heads.push(beam);
},
Object::Splitter(splitter) => {
for direction in splitter.new_directions(beam.direction) {
beam_heads.push(Beam { pos: beam.pos.next_pos(direction), direction });
}
},
}
} else {
beam.pos = beam.pos.next_pos(beam.direction);
beam_heads.push(beam);
}
}
beams = beam_heads;
}
}
fn tiles_energized(&self) -> usize {
self.energized.keys().len()
}
fn _print_map(&self) {
for y in 0 .. self.height {
for x in 0 .. self.width {
if let Some(directions) = self.energized.get(&Position { x, y }) {
if directions.len() == 1 {
match directions[0] {
Direction::Up => print!("^"),
Direction::Down => print!("v"),
Direction::Left => print!("<"),
Direction::Right => print!(">"),
}
} else {
print!("{}", directions.len());
}
} else {
print!(".");
}
}
println!();
}
}
}
fn energized_tiles(input: &[String]) -> usize {
let mut map = Map::new(input);
map.energize(Beam { pos: Position { x: 0, y: 0 }, direction: Direction::Right });
map.tiles_energized()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
r".|...\....",
r"|.-.\.....",
r".....|-...",
r"........|.",
r"..........",
r".........\",
r"..../.\\..",
r".-.-/..|..",
r".|....-|.\",
r"..//.|....",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(energized_tiles(&input), 46);
}
}
|
