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|
use nalgebra::Point2;
use nom::{
branch::alt,
character::complete::{char, line_ending},
combinator::{map, value},
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_23.txt")?;
let forest_map = ForestMap::parser(&input).unwrap().1;
dbg!(forest_map.longest_end_path_length(true));
dbg!(forest_map.longest_end_path_length(false));
Ok(())
}
#[derive(Debug)]
struct ForestMap(Vec<Vec<ForestTile>>);
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum ForestTile {
Wall,
Open,
SlopeUp,
SlopeDown,
SlopeLeft,
SlopeRight,
}
#[derive(Debug, Clone)]
struct DecisionNode {
explored: HashSet<Point2<usize>>,
current: Point2<usize>,
}
impl ForestMap {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(line_ending, many1(ForestTile::parser)),
ForestMap,
)(input)
}
fn longest_end_path_length(&self, slippery: bool) -> usize {
let start_point = Point2::new(1, 0);
let end_point = Point2::new(self.0[0].len() - 2, self.0.len() - 1);
let mut active_nodes = vec![DecisionNode {
explored: HashSet::new(),
current: start_point,
}];
active_nodes[0].explored.insert(start_point);
let mut longest_end_path_length: Option<usize> = None;
while let Some(mut node) = active_nodes.pop() {
let mut all_adjacent = self.adjacent(&node.current, &node.explored, slippery);
while all_adjacent.len() == 1 {
let adjacent = all_adjacent[0];
node.explored.insert(adjacent);
node.current = adjacent;
if node.current == end_point {
let end_path_length = node.path_length();
longest_end_path_length = if let Some(current_longest) = longest_end_path_length
{
Some(current_longest.max(end_path_length))
} else {
Some(end_path_length)
};
all_adjacent = vec![];
} else {
all_adjacent = self.adjacent(&node.current, &node.explored, slippery);
}
}
for adjacent in all_adjacent {
let mut new_node = node.clone();
new_node.explored.insert(adjacent);
new_node.current = adjacent;
if new_node.current == end_point {
let end_path_length = new_node.path_length();
longest_end_path_length = if let Some(current_longest) = longest_end_path_length
{
Some(current_longest.max(end_path_length))
} else {
Some(end_path_length)
};
} else {
active_nodes.push(new_node);
}
}
}
longest_end_path_length.unwrap()
}
fn adjacent(
&self,
p: &Point2<usize>,
not_these: &HashSet<Point2<usize>>,
slippery: bool,
) -> Vec<Point2<usize>> {
let mut adjacent = Vec::with_capacity(4);
let tile = self.at(p);
if p.x > 0 && (!slippery || matches!(tile, ForestTile::Open | ForestTile::SlopeLeft)) {
adjacent.push(Point2::new(p.x - 1, p.y));
}
if p.y > 0 && (!slippery || matches!(tile, ForestTile::Open | ForestTile::SlopeUp)) {
adjacent.push(Point2::new(p.x, p.y - 1));
}
if p.x < self.0[p.y].len() - 1
&& (!slippery || matches!(tile, ForestTile::Open | ForestTile::SlopeRight))
{
adjacent.push(Point2::new(p.x + 1, p.y));
}
if p.y < self.0.len() - 1
&& (!slippery || matches!(tile, ForestTile::Open | ForestTile::SlopeDown))
{
adjacent.push(Point2::new(p.x, p.y + 1));
}
adjacent.retain(|adj_p| self.at(adj_p) != ForestTile::Wall && !not_these.contains(adj_p));
adjacent
}
fn at(&self, p: &Point2<usize>) -> ForestTile {
self.0[p.y][p.x]
}
}
impl ForestTile {
fn parser(input: &str) -> IResult<&str, Self> {
alt((
value(ForestTile::Wall, char('#')),
value(ForestTile::Open, char('.')),
value(ForestTile::SlopeUp, char('^')),
value(ForestTile::SlopeDown, char('v')),
value(ForestTile::SlopeLeft, char('<')),
value(ForestTile::SlopeRight, char('>')),
))(input)
}
}
impl DecisionNode {
fn path_length(&self) -> usize {
self.explored.len() - 1
}
}
|
