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mod.rs
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mod.rs
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use pathfinding::prelude::dijkstra;
use std::collections::HashMap;
use anyhow::{Context, Result};
type Coords = (isize, isize);
type Map = HashMap<Coords, char>;
#[aoc_generator(day12)]
pub fn input_generator(input: &str) -> Result<Map> {
Ok(input
.lines()
.filter(|s| !s.trim().is_empty())
.enumerate()
.flat_map(move |(y, l)| {
l.trim().chars()
.enumerate()
.map(move |(x, c)| ((x as isize, y as isize), c))
})
.collect::<HashMap<_, _>>())
}
fn find_start(map: &Map) -> Option<Coords> {
map.iter()
.find(|&(_, &height)| height == 'S')
.map(|(&pos, _)| pos)
}
fn get_elevation(e: char) -> isize {
match e {
'S' => 1,
'E' => 26,
'a'..='z' => (e as isize) - 96,
// make this one unreachable for any point on our map
_ => 500,
}
}
fn successors(map: &Map, pos: &Coords) -> Vec<(Coords, usize)> {
let possible_neighbors = vec![(-1, 0), (1, 0), (0, 1), (0, -1)];
let mut successors = vec![];
if let Some(&entry) = map.get(pos) {
let level = get_elevation(entry);
for pn in possible_neighbors.iter() {
let p = (pos.0 + pn.0, pos.1 + pn.1);
if let Some(&n) = map.get(&p) {
let l = get_elevation(n);
if l - level <= 1 {
successors.push((p, 1));
}
}
}
}
successors
}
fn shortest_path(map: &Map, start: Coords) -> Option<usize> {
let result = dijkstra(
&start,
|pos| successors(map, pos),
|pos| if let Some(&level) = map.get(pos) {
level == 'E'
} else {
false
}
)?;
Some(result.1)
}
#[aoc(day12, part1)]
pub fn solve_part1(input: &Map) -> Result<usize> {
let start = find_start(input).context("No start found")?;
let result = shortest_path(input, start).context("Dijkstra failed")?;
Ok(result)
}
#[aoc(day12, part2)]
pub fn solve_part2(input: &Map) -> Result<usize> {
let mut results = input
.iter()
.filter(|&(_, &c)| c == 'a' || c == 'S')
.filter_map(|(s, _)| Some((*s, shortest_path(input, *s)?)))
.collect::<Vec<_>>();
results.sort_by(|a, b| a.1.cmp(&b.1));
let shortest_start = results.first().context("Dijkstra failed")?.1;
Ok(shortest_start)
}
#[cfg(test)]
mod test {
use super::*;
fn sample() -> &'static str {
"Sabqponm
abcryxxl
accszExk
acctuvwj
abdefghi"
}
fn input() -> Result<Map> {
input_generator(sample())
}
#[test]
fn part1_sample() -> Result<()> {
let data = input()?;
Ok(assert_eq!(31, solve_part1(&data)?))
}
#[test]
fn part2_sample() -> Result<()> {
let data = input()?;
Ok(assert_eq!(29, solve_part2(&data)?))
}
}