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use std::collections::{HashSet, VecDeque};
#[derive(Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash)]
enum Object {
Microchip(u8),
Generator(u8),
}
impl Object {
fn is_microchip(self) -> bool {
match self {
Object::Microchip(_) => true,
_ => false,
}
}
fn is_generator(self) -> bool {
match self {
Object::Generator(_) => true,
_ => false,
}
}
fn generator(self) -> Self {
match self {
Object::Microchip(k) => Object::Generator(k),
_ => self,
}
}
}
#[derive(Default, Clone)]
struct Floor {
objects: HashSet<Object>,
}
impl Floor {
fn is_empty(&self) -> bool {
self.objects.is_empty()
}
fn is_safe(&self) -> bool {
for &chip in self.objects.iter().filter(|&&o| o.is_microchip()) {
let accompanied = self.objects.contains(&chip.generator());
let generator = self.objects.iter().any(|&o| o.is_generator());
if !accompanied && generator { return false }
}
true
}
}
#[derive(Clone)]
struct State {
steps: u32,
floors: Box<[Floor]>,
elevator: usize,
}
impl State {
fn is_goal(&self) -> bool {
self.floors[0..3].iter().all(Floor::is_empty)
}
fn is_safe(&self) -> bool {
self.floors.iter().all(Floor::is_safe)
}
fn clone_up(&self) -> Self {
let mut state = self.clone();
state.steps += 1;
state.elevator += 1;
state
}
fn clone_down(&self) -> Self {
let mut state = self.clone();
state.steps += 1;
state.elevator -= 1;
state
}
fn generate_states(&self, states: &mut VecDeque<State>) {
for &object in &self.floors[self.elevator].objects {
for &other in &self.floors[self.elevator].objects {
if other == object { continue }
if self.elevator != 3 {
let mut state = self.clone_up();
state.floors[self.elevator].objects.remove(&object);
state.floors[self.elevator].objects.remove(&other);
state.floors[state.elevator].objects.insert(object);
state.floors[state.elevator].objects.insert(other);
if state.is_safe() { states.push_back(state) }
}
if self.elevator != 0 {
let mut state = self.clone_down();
state.floors[self.elevator].objects.remove(&object);
state.floors[self.elevator].objects.remove(&other);
state.floors[state.elevator].objects.insert(object);
state.floors[state.elevator].objects.insert(other);
if state.is_safe() { states.push_back(state) }
}
}
if self.elevator != 3 {
let mut state = self.clone_up();
state.floors[self.elevator].objects.remove(&object);
state.floors[state.elevator].objects.insert(object);
if state.is_safe() { states.push_back(state) }
}
if self.elevator != 0 {
let mut state = self.clone_down();
state.floors[self.elevator].objects.remove(&object);
state.floors[state.elevator].objects.insert(object);
if state.is_safe() { states.push_back(state) }
}
}
}
}
fn solve(floors: Vec<Floor>) -> u32 {
let mut visited = HashSet::new();
let mut states = VecDeque::new();
states.push_back(State { steps: 0, floors: floors.into_boxed_slice(), elevator: 0 });
while let Some(state) = states.pop_front() {
if state.is_goal() {
return state.steps;
}
let visit_floors: Vec<_> = state.floors.iter().map(|floor| {
let mut vec: Vec<_> = floor.objects.iter().cloned().collect();
vec.sort();
vec
}).collect();
if visited.insert((state.elevator, visit_floors)) {
state.generate_states(&mut states);
}
}
unreachable!()
}
fn main() {
// The first floor contains a promethium generator and a promethium-compatible microchip.
// The second floor contains a cobalt generator, a curium generator, a ruthenium generator, and a plutonium generator.
// The third floor contains a cobalt-compatible microchip, a curium-compatible microchip, a ruthenium-compatible microchip, and a plutonium-compatible microchip.
// The fourth floor contains nothing relevant.
const PROMETHIUM: u8 = 0;
const COBALT: u8 = 1;
const CURIUM: u8 = 2;
const RUTHENIUM: u8 = 3;
const PLUTONIUM: u8 = 4;
let mut floors = vec![Floor::default(); 4];
floors[0].objects.insert(Object::Generator(PROMETHIUM));
floors[0].objects.insert(Object::Microchip(PROMETHIUM));
floors[1].objects.insert(Object::Generator(COBALT));
floors[1].objects.insert(Object::Generator(CURIUM));
floors[1].objects.insert(Object::Generator(RUTHENIUM));
floors[1].objects.insert(Object::Generator(PLUTONIUM));
floors[2].objects.insert(Object::Microchip(COBALT));
floors[2].objects.insert(Object::Microchip(CURIUM));
floors[2].objects.insert(Object::Microchip(RUTHENIUM));
floors[2].objects.insert(Object::Microchip(PLUTONIUM));
println!("Part 1: {}", solve(floors.clone()));
// An elerium generator.
// An elerium-compatible microchip.
// A dilithium generator.
// A dilithium-compatible microchip.
const ELERIUM: u8 = 5;
const DILITHIUM: u8 = 6;
floors[0].objects.insert(Object::Generator(ELERIUM));
floors[0].objects.insert(Object::Microchip(ELERIUM));
floors[0].objects.insert(Object::Generator(DILITHIUM));
floors[0].objects.insert(Object::Microchip(DILITHIUM));
println!("Part 2: {}", solve(floors));
}
#[test]
#[ignore]
fn part1() {
// The first floor contains a hydrogen-compatible microchip and a lithium-compatible microchip.
// The second floor contains a hydrogen generator.
// The third floor contains a lithium generator.
// The fourth floor contains nothing relevant.
let mut floors = vec![Floor::default(); 4];
floors[0].objects.insert(Object::Microchip(0));
floors[0].objects.insert(Object::Microchip(1));
floors[1].objects.insert(Object::Generator(0));
floors[2].objects.insert(Object::Generator(1));
assert_eq!(11, solve(floors));
}
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