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|
use nom::{
branch::alt,
bytes::complete::tag,
character::complete::line_ending,
combinator::{map, value},
multi::{many1, separated_list1},
sequence::{delimited, tuple},
IResult,
};
use std::{collections::BTreeSet, fs};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_24.txt")?;
let blizzard_map = BlizzardMap::parser(&input).unwrap().1;
let start = Point { x: 0, y: 0 };
let end = Point {
x: blizzard_map.width - 1,
y: blizzard_map.height - 1,
};
let there_the_first_time =
dbg!(blizzard_map.find_shortest_path_through(start.clone(), end.clone(), 1));
let back_again = dbg!(blizzard_map.find_shortest_path_through(
end.clone(),
start.clone(),
there_the_first_time + 1
));
dbg!(blizzard_map.find_shortest_path_through(start, end, back_again + 1));
Ok(())
}
#[derive(Debug, Clone, PartialEq, Eq)]
struct BlizzardMap {
width: usize,
height: usize,
blizzards: Vec<Blizzard>,
}
#[derive(Debug, Clone, PartialEq, Eq)]
struct Blizzard {
start: Point,
direction: Direction,
}
#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct Point {
y: usize,
x: usize,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
enum Direction {
North,
South,
West,
East,
}
impl BlizzardMap {
fn parser(input: &str) -> IResult<&str, Self> {
map(
delimited(
tuple((many1(tag("#")), tag("."), many1(tag("#")), line_ending)),
separated_list1(
line_ending,
delimited(tag("#"), many1(Direction::parser), tag("#")),
),
tuple((line_ending, many1(tag("#")), tag("."), many1(tag("#")))),
),
|blizzard_directions| BlizzardMap {
width: blizzard_directions[0].len(),
height: blizzard_directions.len(),
blizzards: blizzard_directions
.into_iter()
.enumerate()
.flat_map(|(y, row)| {
row.into_iter()
.enumerate()
.filter_map(move |(x, direction)| {
direction.map(|direction| Blizzard {
start: Point { x, y },
direction,
})
})
})
.collect(),
},
)(input)
}
fn find_shortest_path_through(
&self,
start: Point,
end: Point,
mut current_round: usize,
) -> usize {
// Not sure if "visited" makes sense here because of the time
// delay. Same position at different times is different. Maybe
// makes sense if I keep time in too.
let mut frontier = BTreeSet::new();
frontier.insert(start);
while !frontier.contains(&end) {
current_round += 1;
let last_frontier = std::mem::take(&mut frontier);
let blizzards = self.blizzards_at_time(current_round);
for frontier_state in last_frontier {
let mut possible_moves = vec![frontier_state.clone()];
if frontier_state.x > 0 {
possible_moves.push(Point {
x: frontier_state.x - 1,
y: frontier_state.y,
});
}
if frontier_state.x < self.width - 1 {
possible_moves.push(Point {
x: frontier_state.x + 1,
y: frontier_state.y,
});
}
if frontier_state.y > 0 {
possible_moves.push(Point {
x: frontier_state.x,
y: frontier_state.y - 1,
});
}
if frontier_state.y < self.height - 1 {
possible_moves.push(Point {
x: frontier_state.x,
y: frontier_state.y + 1,
});
}
for next in possible_moves {
if !blizzards.contains(&next) {
frontier.insert(next);
}
}
}
}
current_round + 1 // extra minute to leave
}
fn blizzards_at_time(&self, t: usize) -> BTreeSet<Point> {
self.blizzards
.iter()
.map(|blizzard| match blizzard.direction {
Direction::North => {
let t = t % self.height;
Point {
y: if blizzard.start.y > t {
blizzard.start.y - t
} else {
blizzard.start.y + self.height - t
},
..blizzard.start
}
}
Direction::South => Point {
y: (blizzard.start.y + t) % self.height,
..blizzard.start
},
Direction::West => {
let t = t % self.width;
Point {
x: if blizzard.start.x > t {
blizzard.start.x - t
} else {
blizzard.start.x + self.width - t
},
..blizzard.start
}
}
Direction::East => Point {
x: (blizzard.start.x + t) % self.width,
..blizzard.start
},
})
.collect()
}
}
impl Direction {
fn parser(input: &str) -> IResult<&str, Option<Self>> {
alt((
value(None, tag(".")),
value(Some(Direction::South), tag("v")),
value(Some(Direction::West), tag("<")),
value(Some(Direction::East), tag(">")),
value(Some(Direction::North), tag("^")),
))(input)
}
}
|
