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use std::collections::HashMap;
static DAY: u8 = 10;
fn main() {
let input = advent::read_lines(DAY);
println!("{DAY}a: {}", steps_to_farthest(&input));
println!("{DAY}b: {}", 0);
}
#[derive(Clone, Copy, PartialEq, Eq)]
enum Direction {
North,
South,
East,
West,
}
impl Direction {
fn from(c: char) -> [Direction; 2] {
match c {
'|' => [Direction::South, Direction::North],
'-' => [Direction::West, Direction::East],
'L' => [Direction::North, Direction::East],
'J' => [Direction::North, Direction::West],
'7' => [Direction::South, Direction::West],
'F' => [Direction::South, Direction::East],
_ => panic!("unexpected pipe"),
}
}
fn opposite(&self) -> Direction {
match *self {
Direction::North => Direction::South,
Direction::South => Direction::North,
Direction::West => Direction::East,
Direction::East => Direction::West,
}
}
}
#[derive(PartialEq, Eq, Hash, Clone, Copy)]
struct Position {
x: isize,
y: isize,
}
struct Map {
start: Position,
pipes: HashMap<Position, [Direction; 2]>,
}
impl Map {
fn new(input: &[String]) -> Map {
let mut start = Position { x: 0, y: 0 };
let mut pipes = 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 };
match c {
'S' => { start = pos },
'.' => continue,
pipe => { pipes.insert(pos, Direction::from(pipe)); },
}
}
}
Map { start, pipes }
}
fn pos_connectable(&self, pos: &Position, from_direction: Direction) -> bool {
if *pos == self.start {
/* pipe at start is unknown; assume that it can connect to anything */
true
} else if let Some(directions) = self.pipes.get(pos) {
match from_direction {
Direction::North => { directions.contains(&Direction::South) },
Direction::South => { directions.contains(&Direction::North) },
Direction::East => { directions.contains(&Direction::West) },
Direction::West => { directions.contains(&Direction::East) },
}
} else {
false
}
}
fn remove_disconnected_pipes(&mut self) {
let mut disconnected_pipes = Vec::new();
loop {
disconnected_pipes.clear();
for (pos, directions) in &self.pipes {
for direction in directions {
match direction {
Direction::North => if !self.pos_connectable(&Position { x: pos.x, y: pos.y - 1 }, *direction) { disconnected_pipes.push(*pos); },
Direction::South => if !self.pos_connectable(&Position { x: pos.x, y: pos.y + 1 }, *direction) { disconnected_pipes.push(*pos); },
Direction::West => if !self.pos_connectable(&Position { x: pos.x - 1, y: pos.y }, *direction) { disconnected_pipes.push(*pos); },
Direction::East => if !self.pos_connectable(&Position { x: pos.x + 1, y: pos.y }, *direction) { disconnected_pipes.push(*pos); },
}
}
}
for pos in &disconnected_pipes {
self.pipes.remove(pos);
}
if disconnected_pipes.is_empty() {
break;
}
}
}
fn other_direction(&self, pos: &Position, direction: Direction) -> Direction {
/* get the direction from the other end of the pipe */
let directions = self.pipes.get(pos).unwrap();
if directions[0] == direction {
directions[1]
} else {
directions[0]
}
}
fn count_steps(&self) -> u32 {
let mut steps = 0;
let mut pos = self.start;
let mut direction = Direction::North;
/* check for possible connection from starting position */
if self.pos_connectable(&Position { x: pos.x, y: pos.y - 1 }, Direction::North) { direction = Direction::North; }
else if self.pos_connectable(&Position { x: pos.x, y: pos.y + 1 }, Direction::South) { direction = Direction::South; }
else if self.pos_connectable(&Position { x: pos.x - 1, y: pos.y }, Direction::West) { direction = Direction::West; }
else if self.pos_connectable(&Position { x: pos.x + 1, y: pos.y }, Direction::East) { direction = Direction::East; }
loop {
let next_pos = match direction {
Direction::North => Position { x: pos.x, y: pos.y - 1 },
Direction::South => Position { x: pos.x, y: pos.y + 1 },
Direction::West => Position { x: pos.x - 1, y: pos.y },
Direction::East => Position { x: pos.x + 1, y: pos.y },
};
steps += 1;
if next_pos == self.start {
break;
}
direction = self.other_direction(&next_pos, direction.opposite());
pos = next_pos;
}
steps
}
fn _print_map(&self) {
let max_x = self.pipes.keys().map(|pos| pos.x).max().unwrap();
let max_y = self.pipes.keys().map(|pos| pos.y).max().unwrap();
for y in 0 ..= max_y {
for x in 0 ..= max_x {
let pos = Position { x, y };
if pos == self.start {
print!("S");
continue;
}
if let Some(direction) = self.pipes.get(&pos) {
match direction {
[Direction::South, Direction::North] => { print!("|"); },
[Direction::West, Direction::East] => { print!("-"); },
[Direction::North, Direction::East] => { print!("L"); },
[Direction::North, Direction::West] => { print!("J"); },
[Direction::South, Direction::West] => { print!("7"); },
[Direction::South, Direction::East] => { print!("F"); },
_ => panic!("unexpected directions"),
}
} else {
print!(".");
}
}
println!();
}
}
}
fn steps_to_farthest(input: &[String]) -> u32 {
let mut map = Map::new(input);
map.remove_disconnected_pipes();
map.count_steps() / 2
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test() {
let input = [
"-L|F7",
"7S-7|",
"L|7||",
"-L-J|",
"L|-JF",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(steps_to_farthest(&input), 4);
let input = [
"7-F7-",
".FJ|7",
"SJLL7",
"|F--J",
"LJ.LJ",
].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
assert_eq!(steps_to_farthest(&input), 8);
}
}
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