144 lines
3.2 KiB
Rust
144 lines
3.2 KiB
Rust
use std::{
|
|
collections::{HashMap, HashSet},
|
|
fs::read_to_string,
|
|
};
|
|
|
|
pub fn day_main() {
|
|
let input = read_to_string("input/day06.txt").unwrap();
|
|
let input = input.trim();
|
|
println!(" part1: {}", part1(input));
|
|
println!(" part2: {}", part2(input));
|
|
}
|
|
|
|
type RiddleResult = usize;
|
|
type Point = (i32, i32);
|
|
|
|
fn part1(input: &str) -> RiddleResult {
|
|
let (m, pos) = parse(input);
|
|
|
|
let dir = '^';
|
|
let visited = get_visited(&m, pos, dir);
|
|
visited.len()
|
|
}
|
|
|
|
fn get_visited(
|
|
m: &HashMap<(i32, i32), char>,
|
|
mut pos: (i32, i32),
|
|
mut dir: char,
|
|
) -> HashSet<(i32, i32)> {
|
|
let mut visited = HashSet::new();
|
|
while m.contains_key(&pos) {
|
|
let (x, y) = pos;
|
|
visited.insert(pos);
|
|
let next = match dir {
|
|
'^' => (x, y - 1),
|
|
'v' => (x, y + 1),
|
|
'<' => (x - 1, y),
|
|
'>' => (x + 1, y),
|
|
_ => unreachable!(),
|
|
};
|
|
if let Some('#') = m.get(&next) {
|
|
dir = match dir {
|
|
'^' => '>',
|
|
'v' => '<',
|
|
'<' => '^',
|
|
'>' => 'v',
|
|
_ => unreachable!("asdf"),
|
|
};
|
|
} else {
|
|
pos = next;
|
|
}
|
|
}
|
|
visited
|
|
}
|
|
|
|
fn part2(input: &str) -> RiddleResult {
|
|
let (m, pos) = parse(input);
|
|
|
|
let dir = '^';
|
|
get_visited(&m, pos, dir)
|
|
.into_iter()
|
|
.filter(|open| is_loop(&m, *open, pos, dir))
|
|
.count()
|
|
}
|
|
|
|
fn parse(input: &str) -> (HashMap<Point, char>, Point) {
|
|
let mut m = HashMap::new();
|
|
let mut pos = None;
|
|
input.lines().enumerate().for_each(|(y, line)| {
|
|
line.char_indices().for_each(|(x, c)| {
|
|
let x = x as i32;
|
|
let y = y as i32;
|
|
if c == '^' {
|
|
pos = Some((x, y));
|
|
m.insert((x, y), '.');
|
|
} else {
|
|
m.insert((x, y), c);
|
|
}
|
|
});
|
|
});
|
|
(m, pos.unwrap())
|
|
}
|
|
|
|
fn is_loop(m: &HashMap<Point, char>, block: Point, mut pos: Point, mut dir: char) -> bool {
|
|
let mut visited = HashSet::new();
|
|
loop {
|
|
let (x, y) = pos;
|
|
|
|
let next = match dir {
|
|
'^' => (x, y - 1),
|
|
'v' => (x, y + 1),
|
|
'<' => (x - 1, y),
|
|
'>' => (x + 1, y),
|
|
_ => unreachable!(),
|
|
};
|
|
let next_tile = m.get(&next);
|
|
if None == next_tile {
|
|
return false;
|
|
} else if next == block || Some(&'#') == next_tile {
|
|
// we only check for loops on a collision to speed things up
|
|
if visited.contains(&(pos, dir)) {
|
|
return true;
|
|
}
|
|
visited.insert((pos, dir));
|
|
|
|
dir = match dir {
|
|
'^' => '>',
|
|
'v' => '<',
|
|
'<' => '^',
|
|
'>' => 'v',
|
|
_ => unreachable!("asdf"),
|
|
};
|
|
} else {
|
|
pos = next;
|
|
}
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod test {
|
|
use super::{part1, part2};
|
|
|
|
const TEST_INPUT: &str = r"....#.....
|
|
.........#
|
|
..........
|
|
..#.......
|
|
.......#..
|
|
..........
|
|
.#..^.....
|
|
........#.
|
|
#.........
|
|
......#...
|
|
";
|
|
|
|
#[test]
|
|
fn test1() {
|
|
assert_eq!(part1(TEST_INPUT), 41);
|
|
}
|
|
|
|
#[test]
|
|
fn test2() {
|
|
assert_eq!(part2(TEST_INPUT), 6);
|
|
}
|
|
}
|