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|
use nom::{
branch::alt,
bytes::complete::tag,
character::complete::{char as nom_char, line_ending, not_line_ending},
combinator::value,
multi::{many1, separated_list1},
sequence::{delimited, pair},
IResult,
};
use std::{cmp, collections::HashSet, fs};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_23.txt")?;
let maze = parse_maze(&input).unwrap().1;
dbg!(find_shortest_path(&maze).cost);
Ok(())
}
fn find_shortest_path(maze: &Maze) -> Move {
let mut visited = HashSet::new();
visited.insert(maze.clone());
let mut frontier = vec![Move {
next_state: maze.clone(),
cost: 0,
}];
let mut best_so_far: Option<Move> = None;
while let Some(current) = frontier.pop() {
if let Some(best_so_far) = &best_so_far {
if current.cost >= best_so_far.cost {
return best_so_far.clone();
}
}
let next_moves: Vec<Move> = current
.next_state
.valid_moves()
.into_iter()
.map(|next| Move {
cost: next.cost + current.cost,
..next
})
.collect();
for next in next_moves {
if next.next_state.is_complete() {
best_so_far = if let Some(best_so_far) = best_so_far {
if best_so_far.cost < next.cost {
Some(best_so_far)
} else {
Some(next.clone())
}
} else {
Some(next.clone())
};
} else if !visited.contains(&next.next_state) {
visited.insert(next.next_state.clone());
frontier.push(next);
}
}
frontier.sort_unstable_by(|a, b| b.cost.cmp(&a.cost));
}
best_so_far.expect("There is no path through!")
}
#[derive(Debug, Clone)]
struct Move {
next_state: Maze,
cost: usize,
}
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct Maze {
corridor: Vec<Option<usize>>,
rooms: Vec<Room>,
}
impl Maze {
fn is_complete(&self) -> bool {
self.rooms.iter().all(|room| room.is_complete())
}
fn valid_moves(&self) -> Vec<Move> {
let mut valid_moves = Vec::new();
for i in 0..self.corridor.len() {
if let Some(shrimp) = self.corridor[i] {
let target_room = &self.rooms[shrimp / 2 - 1];
if target_room.can_enter() {
let route_free = (cmp::min(shrimp, i)..=cmp::max(shrimp, i))
.all(|route_i| route_i == i || self.corridor[route_i].is_none());
if route_free {
let mut next_state = self.clone();
next_state.corridor[i] = None;
let next_room = &mut next_state.rooms[shrimp / 2 - 1];
let room_depth = next_room
.max_free()
.expect("no space in room, but we checked!");
next_room.contents[room_depth] = Some(shrimp);
let distance = room_depth + 1 + cmp::max(shrimp, i) - cmp::min(shrimp, i);
let cost = calculate_cost(shrimp, distance);
valid_moves.push(Move { next_state, cost });
}
}
}
}
for (room_i, room) in self
.rooms
.iter()
.enumerate()
.filter(|(_, room)| !room.can_enter())
{
if let Some((room_depth, shrimp)) = room
.contents
.iter()
.enumerate()
.filter_map(|(room_depth, maybe_shrimp)| {
maybe_shrimp.map(|shrimp| (room_depth, shrimp))
})
.next()
{
for corridor_i in 0..self.corridor.len() {
let in_entrance = self.rooms.iter().any(|room| room.entrance == corridor_i);
let route_free = (cmp::min(room.entrance, corridor_i)
..=cmp::max(room.entrance, corridor_i))
.all(|route_i| self.corridor[route_i].is_none());
if !in_entrance && route_free {
let mut next_state = self.clone();
next_state.corridor[corridor_i] = Some(shrimp);
next_state.rooms[room_i].contents[room_depth] = None;
let distance = room_depth + 1 + cmp::max(room.entrance, corridor_i)
- cmp::min(room.entrance, corridor_i);
let cost = calculate_cost(shrimp, distance);
valid_moves.push(Move { next_state, cost });
}
}
}
}
valid_moves
}
}
fn calculate_cost(shrimp: usize, distance: usize) -> usize {
let shrimp_cost = match shrimp {
2 => 1,
4 => 10,
6 => 100,
8 => 1000,
_ => panic!("Unknown shrimp"),
};
shrimp_cost * distance
}
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct Room {
entrance: usize,
contents: Vec<Option<usize>>,
}
impl Room {
fn is_complete(&self) -> bool {
self.contents
.iter()
.all(|slot| slot == &Some(self.entrance))
}
fn can_enter(&self) -> bool {
self.contents
.iter()
.all(|slot| slot.is_none() || slot == &Some(self.entrance))
}
fn max_free(&self) -> Option<usize> {
self.contents.iter().rposition(|slot| slot.is_none())
}
}
fn parse_maze(input: &str) -> IResult<&str, Maze> {
let (input, _) = pair(not_line_ending, line_ending)(input)?; // skip first line
let (input, corridor) = delimited(nom_char('#'), many1(corridor_contents), tag("#\n"))(input)?;
let (input, rooms_line_1) = delimited(
tag("###"),
separated_list1(nom_char('#'), corridor_contents),
tag("###\n"),
)(input)?;
let (input, rooms_line_2) = delimited(
tag(" #"),
separated_list1(nom_char('#'), corridor_contents),
tag("#\n"),
)(input)?;
let rooms = vec![
Room {
entrance: 2,
contents: vec![rooms_line_1[0], Some(8), Some(8), rooms_line_2[0]],
},
Room {
entrance: 4,
contents: vec![rooms_line_1[1], Some(6), Some(4), rooms_line_2[1]],
},
Room {
entrance: 6,
contents: vec![rooms_line_1[2], Some(4), Some(2), rooms_line_2[2]],
},
Room {
entrance: 8,
contents: vec![rooms_line_1[3], Some(2), Some(6), rooms_line_2[3]],
},
];
Ok((input, Maze { corridor, rooms }))
}
fn corridor_contents(input: &str) -> IResult<&str, Option<usize>> {
alt((
value(None, nom_char('.')),
value(Some(2), nom_char('A')),
value(Some(4), nom_char('B')),
value(Some(6), nom_char('C')),
value(Some(8), nom_char('D')),
))(input)
}
|
