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advent_of_code::solution!(17); | ||
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use std::cmp::Ordering; | ||
use std::collections::{BinaryHeap, HashMap}; | ||
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#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)] | ||
enum Direction { | ||
Up, | ||
Down, | ||
Left, | ||
Right, | ||
} | ||
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impl Direction { | ||
fn valid_next(self, dir_count: usize, part2: bool) -> Vec<Self> { | ||
let mut ret = Vec::with_capacity(3); | ||
match self { | ||
Direction::Up => { | ||
if !part2 { | ||
if dir_count < 3 { | ||
ret.push(Self::Up); | ||
} | ||
ret.push(Self::Right); | ||
ret.push(Self::Left); | ||
} else { | ||
if dir_count < 10 { | ||
ret.push(Self::Up) | ||
} | ||
if dir_count >= 4 { | ||
ret.push(Self::Right); | ||
ret.push(Self::Left); | ||
} | ||
} | ||
} | ||
Direction::Down => { | ||
if !part2 { | ||
if dir_count < 3 { | ||
ret.push(Self::Down); | ||
} | ||
ret.push(Self::Right); | ||
ret.push(Self::Left); | ||
} else { | ||
if dir_count < 10 { | ||
ret.push(Self::Down) | ||
} | ||
if dir_count >= 4 { | ||
ret.push(Self::Right); | ||
ret.push(Self::Left); | ||
} | ||
} | ||
} | ||
Direction::Left => { | ||
if !part2 { | ||
if dir_count < 3 { | ||
ret.push(Self::Left); | ||
} | ||
ret.push(Self::Up); | ||
ret.push(Self::Down); | ||
} else { | ||
if dir_count < 10 { | ||
ret.push(Self::Left) | ||
} | ||
if dir_count >= 4 { | ||
ret.push(Self::Up); | ||
ret.push(Self::Down); | ||
} | ||
} | ||
} | ||
Direction::Right => { | ||
if !part2 { | ||
if dir_count < 3 { | ||
ret.push(Self::Right); | ||
} | ||
ret.push(Self::Up); | ||
ret.push(Self::Down); | ||
} else { | ||
if dir_count < 10 { | ||
ret.push(Self::Right) | ||
} | ||
if dir_count >= 4 { | ||
ret.push(Self::Up); | ||
ret.push(Self::Down); | ||
} | ||
} | ||
} | ||
} | ||
ret | ||
} | ||
} | ||
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#[derive(Copy, Clone, Eq, PartialEq)] | ||
struct State { | ||
cost: usize, | ||
position: (usize, usize), | ||
direction: Direction, | ||
dir_count: usize, | ||
} | ||
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impl Ord for State { | ||
fn cmp(&self, other: &Self) -> Ordering { | ||
other | ||
.cost | ||
.cmp(&self.cost) | ||
.then_with(|| self.position.cmp(&other.position)) | ||
} | ||
} | ||
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impl PartialOrd for State { | ||
fn partial_cmp(&self, other: &Self) -> Option<Ordering> { | ||
Some(self.cmp(other)) | ||
} | ||
} | ||
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fn valid_neighbors( | ||
map: &[Vec<usize>], | ||
position: (usize, usize), | ||
direction: Direction, | ||
dir_count: usize, | ||
part2: bool, | ||
) -> Vec<((usize, usize), Direction)> { | ||
let ret = Vec::new(); | ||
direction | ||
.valid_next(dir_count, part2) | ||
.iter() | ||
.fold(ret, |mut acc, dir| { | ||
match dir { | ||
Direction::Up if position.0 > 0 => { | ||
acc.push(((position.0 - 1, position.1), Direction::Up)) | ||
} | ||
Direction::Down if position.0 < map.len() - 1 => { | ||
acc.push(((position.0 + 1, position.1), Direction::Down)) | ||
} | ||
Direction::Left if position.1 > 0 => { | ||
acc.push(((position.0, position.1 - 1), Direction::Left)) | ||
} | ||
Direction::Right if position.1 < map[0].len() - 1 => { | ||
acc.push(((position.0, position.1 + 1), Direction::Right)) | ||
} | ||
_ => {} | ||
}; | ||
acc | ||
}) | ||
} | ||
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fn shortest_path( | ||
map: &[Vec<usize>], | ||
start: (usize, usize), | ||
goal: (usize, usize), | ||
part2: bool, | ||
) -> Option<u64> { | ||
let mut dist: HashMap<((usize, usize), Direction, usize), usize> = HashMap::new(); | ||
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let mut heap = BinaryHeap::new(); | ||
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heap.push(State { | ||
cost: 0, | ||
position: start, | ||
direction: Direction::Right, // dummy value | ||
dir_count: 0, // don't count toward limit | ||
}); | ||
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while let Some(State { | ||
cost, | ||
position, | ||
direction, | ||
dir_count, | ||
}) = heap.pop() | ||
{ | ||
if position == goal { | ||
if part2 && dir_count < 4 { | ||
continue; | ||
} | ||
return Some(cost as u64); | ||
} | ||
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if let Some(found) = dist.get(&(position, direction, dir_count)) { | ||
if *found < cost { | ||
continue; | ||
} | ||
} | ||
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for (new_pos, new_dir) in valid_neighbors(&map, position, direction, dir_count, part2) { | ||
let next = State { | ||
cost: cost + map[new_pos.0][new_pos.1], | ||
position: new_pos, | ||
direction: new_dir, | ||
dir_count: if new_dir != direction { | ||
1 | ||
} else { | ||
dir_count + 1 | ||
}, | ||
}; | ||
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if let Some(found) = dist.get(&(new_pos, new_dir, next.dir_count)) { | ||
if next.cost < *found { | ||
heap.push(next); | ||
dist.insert((new_pos, new_dir, next.dir_count), next.cost); | ||
} | ||
} else { | ||
heap.push(next); | ||
dist.insert((new_pos, new_dir, next.dir_count), next.cost); | ||
} | ||
} | ||
} | ||
None | ||
} | ||
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pub fn part_one(input: &str) -> Option<u64> { | ||
let map: Vec<Vec<usize>> = input | ||
.lines() | ||
.map(|line| { | ||
line.chars() | ||
.map(|s| s.to_digit(10).expect("All items should be digits") as usize) | ||
.collect() | ||
}) | ||
.collect(); | ||
shortest_path(&map, (0, 0), (map.len() - 1, map[0].len() - 1), false) | ||
} | ||
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pub fn part_two(input: &str) -> Option<u64> { | ||
let map: Vec<Vec<usize>> = input | ||
.lines() | ||
.map(|line| { | ||
line.chars() | ||
.map(|s| s.to_digit(10).expect("All items should be digits") as usize) | ||
.collect() | ||
}) | ||
.collect(); | ||
shortest_path(&map, (0, 0), (map.len() - 1, map[0].len() - 1), true) | ||
} | ||
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#[cfg(test)] | ||
mod tests { | ||
use super::*; | ||
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#[test] | ||
fn test_part_one() { | ||
let result = part_one(&advent_of_code::template::read_file("examples", DAY)); | ||
assert_eq!(result, Some(102)); | ||
} | ||
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#[test] | ||
fn test_part_two() { | ||
let result = part_two(&advent_of_code::template::read_file("examples", DAY)); | ||
assert_eq!(result, Some(94)); | ||
} | ||
} |