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|
use nom::{
character::complete::{line_ending, satisfy},
combinator::map,
multi::{many1, separated_list1},
IResult,
};
use std::{
collections::{BTreeMap, BTreeSet},
fs,
};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_12.txt")?;
let map = HeightMap::parser(&input).unwrap().1;
let distance_map = MapExploration::explore(&map);
dbg!(distance_map.distance_to.get(&map.start));
let min_distance_start = map
.heights
.iter()
.enumerate()
.flat_map(|(y, row)| {
row.iter()
.enumerate()
.filter(|(_x, height)| **height == 0)
.map(move |(x, _)| Point { x, y })
})
.filter_map(|p| distance_map.distance_to.get(&p))
.min();
dbg!(min_distance_start);
Ok(())
}
#[derive(Debug, Clone)]
struct HeightMap {
heights: Vec<Vec<u8>>,
start: Point,
end: Point,
}
#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct Point {
x: usize,
y: usize,
}
impl HeightMap {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(line_ending, many1(satisfy(|c| c.is_ascii_alphabetic()))),
|height_chars| {
let mut start = Point::default();
let mut end = Point::default();
let mut heights = Vec::new();
for y in 0..height_chars.len() {
let mut new_row = Vec::new();
for x in 0..height_chars[y].len() {
let height = match height_chars[y][x] {
'S' => {
start = Point { x, y };
0
}
'E' => {
end = Point { x, y };
25
}
a if a.is_ascii_lowercase() => height_chars[y][x] as u8 - b'a',
a => panic!("Unexpected character {}", a),
};
new_row.push(height);
}
heights.push(new_row);
}
HeightMap {
heights,
start,
end,
}
},
)(input)
}
fn adjacent_to(&self, p: &Point) -> Vec<Point> {
let current_height = self
.heights
.get(p.y)
.and_then(|row| row.get(p.x))
.cloned()
.unwrap_or(0);
p.adjacent()
.into_iter()
.filter(|other_p| {
let other_height = self
.heights
.get(other_p.y)
.and_then(|row| row.get(other_p.x));
match other_height {
None => false,
Some(&other_height) => other_height + 1 >= current_height,
}
})
.collect()
}
}
impl Point {
fn adjacent(&self) -> Vec<Point> {
let mut result = Vec::new();
if self.x > 0 {
result.push(Point {
x: self.x - 1,
y: self.y,
});
}
if self.x < usize::MAX {
result.push(Point {
x: self.x + 1,
y: self.y,
});
}
if self.y > 0 {
result.push(Point {
x: self.x,
y: self.y - 1,
});
}
if self.y < usize::MAX {
result.push(Point {
x: self.x,
y: self.y + 1,
});
}
result
}
}
struct MapExploration {
distance_to: BTreeMap<Point, u32>,
}
impl MapExploration {
fn explore(map: &HeightMap) -> MapExploration {
let mut frontier = BTreeSet::new();
let mut distance_to = BTreeMap::new();
let mut distance = 0;
distance_to.insert(map.end.clone(), distance);
frontier.insert(map.end.clone());
while !frontier.is_empty() {
let mut next_frontier = BTreeSet::new();
distance += 1;
for frontier_point in frontier {
for adjacent_point in map.adjacent_to(&frontier_point) {
if !distance_to.contains_key(&adjacent_point) {
distance_to.insert(adjacent_point.clone(), distance);
next_frontier.insert(adjacent_point);
}
}
}
frontier = next_frontier;
}
MapExploration { distance_to }
}
}
|
