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|
use nalgebra::{DMatrix, Point2, Unit, Vector2};
use nom::{
character::complete::{line_ending, satisfy},
combinator::{map, map_res},
multi::{many1, separated_list1},
IResult,
};
use std::{collections::HashSet, fs};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_17.txt")?;
let parsed = HeatlossMap::parser(&input).unwrap().1;
dbg!(&parsed.find_shortest_heatloss_path());
Ok(())
}
#[derive(Debug)]
struct HeatlossMap(DMatrix<u32>);
#[derive(Debug, Hash, PartialEq, Eq, Clone)]
struct Position {
pos: Point2<isize>,
facing: Unit<Vector2<isize>>,
duration_with_facing: usize,
}
impl HeatlossMap {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(
line_ending,
many1(map_res(satisfy(|c| c.is_digit(10)), |d| {
d.to_string().parse::<u32>()
})),
),
|digits_vec| {
HeatlossMap(DMatrix::from_iterator(
digits_vec.len(),
digits_vec[0].len(),
digits_vec.into_iter().flat_map(|row| row.into_iter()),
))
},
)(input)
}
fn find_shortest_heatloss_path(&self) -> u32 {
let start = Position {
pos: Point2::new(0, 0),
facing: Vector2::x_axis(),
duration_with_facing: 0,
};
let end_pos = self.end();
let mut frontier = vec![(0, start.clone())];
let mut visited = HashSet::new();
visited.insert(start);
let mut distance_to_end = None;
while distance_to_end.is_none() && frontier.len() > 0 {
// shortest distance is now at the end
frontier
.sort_unstable_by(|(distance_a, _), (distance_b, _)| distance_b.cmp(distance_a));
let (front_distance, front_position) = frontier.pop().unwrap();
let mut next_points: Vec<Position> = Vec::new();
{
let facing = rotate_left(&front_position.facing);
let pos = front_position.pos + *facing;
next_points.push(Position {
pos,
facing,
duration_with_facing: 1,
});
}
{
let facing = rotate_right(&front_position.facing);
let pos = front_position.pos + *facing;
next_points.push(Position {
pos,
facing,
duration_with_facing: 1,
});
}
if front_position.duration_with_facing < 3 {
let pos = front_position.pos + *front_position.facing;
next_points.push(Position {
pos,
facing: front_position.facing.clone(),
duration_with_facing: front_position.duration_with_facing + 1,
});
}
for next_point in next_points {
if let Some(step_distance) = self.get(&next_point.pos) {
if !visited.contains(&next_point) {
visited.insert(next_point.clone());
let distance = front_distance + step_distance;
if next_point.pos == end_pos {
distance_to_end = Some(distance);
}
frontier.push((distance, next_point));
}
}
}
}
distance_to_end.unwrap()
}
fn end(&self) -> Point2<isize> {
Point2::new(self.0.ncols() as isize - 1, self.0.nrows() as isize - 1)
}
fn get(&self, pos: &Point2<isize>) -> Option<u32> {
let x: Option<usize> = pos.x.try_into().ok();
let y: Option<usize> = pos.y.try_into().ok();
match (x, y) {
(Some(x), Some(y)) => self.0.get((x, y)).copied(),
_ => None,
}
}
}
fn rotate_left(facing: &Unit<Vector2<isize>>) -> Unit<Vector2<isize>> {
Unit::new_unchecked(Vector2::new(-facing.y, facing.x))
}
fn rotate_right(facing: &Unit<Vector2<isize>>) -> Unit<Vector2<isize>> {
Unit::new_unchecked(Vector2::new(facing.y, -facing.x))
}
|
