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|
use aoc2024::matrix;
use std::collections::{HashMap, HashSet};
use std::fmt;
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
enum Direction {
Up,
Right,
Down,
Left,
}
use Direction::*;
impl Direction {
fn rotate(self) -> Self {
match self {
Up => Right,
Right => Down,
Down => Left,
Left => Up,
}
}
}
#[derive(Clone)]
enum Dot {
Empty,
Obstacle,
Visited,
Guard(Direction),
}
use Dot::*;
impl fmt::Display for Dot {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let ch = match self {
Empty => ".",
Obstacle => "#",
Visited => "X",
Guard(Up) => "^",
Guard(Right) => ">",
Guard(Down) => "v",
Guard(Left) => "<",
};
write!(f, "{}", ch)
}
}
impl Dot {
fn parse(c: char) -> Dot {
match c {
'.' => Empty,
'#' => Obstacle,
'X' => Visited,
'^' => Guard(Up),
'>' => Guard(Right),
'v' => Guard(Down),
'<' => Guard(Left),
_ => panic!("Invalid input"),
}
}
}
#[derive(Clone)]
struct M {
matrix: matrix::Matrix<Dot>,
guard: matrix::Pos,
visited: HashMap<matrix::Pos, HashSet<Direction>>,
}
impl M {
fn new(text: &str) -> Self {
let matrix = matrix::Matrix::new(text, Dot::parse);
let mut guard = (0, 0);
let mut visited = HashMap::new();
for i in 0..matrix.limit.0 {
for j in 0..matrix.limit.1 {
if let Guard(dir) = matrix.get((i, j)) {
let mut dirhs = HashSet::new();
dirhs.insert(*dir);
visited.insert(guard, dirhs);
guard = (i, j);
}
}
}
M {
matrix,
guard,
visited,
}
}
}
#[derive(Debug)]
enum SimResult {
OutOfBounds,
Loop,
}
impl M {
fn step(&mut self) -> Option<SimResult> {
let M {
matrix,
guard,
visited,
} = self;
// Compute guard's next position
let Guard(direction) = matrix.get(*guard) else {
panic!("Impossible: {self}")
};
let newpos: (usize, usize) = match direction {
Up if guard.0 > 0 => (guard.0 - 1, guard.1),
Right if guard.1 < matrix.limit.1 - 1 => (guard.0, guard.1 + 1),
Down if guard.0 < matrix.limit.0 - 1 => (guard.0 + 1, guard.1),
Left if guard.1 > 0 => (guard.0, guard.1 - 1),
_ => return Some(SimResult::OutOfBounds),
};
match (matrix.get(newpos), visited.get(guard)) {
(Visited, Some(vs)) if vs.contains(direction) => return Some(SimResult::Loop),
(Empty | Visited, _) => {
let d = *direction;
matrix.set(newpos, Guard(d));
matrix.set(*guard, Visited);
let hs = visited.entry(*guard).or_insert(HashSet::new());
hs.insert(d);
*guard = newpos;
}
(Obstacle, _) => {
matrix.set(*guard, Guard(direction.rotate()));
}
_ => (),
};
// println!("{self}");
None
}
fn step_forever(&mut self) -> SimResult {
loop {
if let Some(res) = self.step() { return res }
}
}
fn count_visited(&self) -> u32 {
let mut result: u32 = 0;
let M { matrix, .. } = self;
for i in 0..matrix.limit.0 {
for j in 0..matrix.limit.1 {
match matrix.get((i, j)) {
Visited | Guard(_) => result += 1,
_ => (),
}
}
}
result
}
}
impl fmt::Display for M {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// write!(f, "{}[2J", 27 as char)?;
write!(f, "{}", self.matrix)?;
write!(f, "[Guard position: {:?}]", self.guard)
}
}
fn p1(input: &str) -> String {
let mut m: M = M::new(input);
println!("{m}");
println!("Result: {:?}", m.step_forever());
println!("{m}");
let result = m.count_visited();
result.to_string()
}
fn count_loops(m: M) -> u32 {
let mut result = 0;
// let mut simulations = 0;
for i in 0..m.matrix.limit.0 {
for j in 0..m.matrix.limit.1 {
if let Empty = m.matrix.get((i, j)) {
// simulations += 1;
let mut m1 = m.clone();
m1.matrix.set((i, j), Obstacle);
// println!("Simulation {simulations} @ ({i},{j}) ({result})...");
// println!("{m1}");
if let SimResult::Loop = m1.step_forever() {
result += 1;
}
}
}
}
result
}
fn p2(input: &str) -> String {
let m: M = M::new(input);
let result = count_loops(m);
result.to_string()
}
fn main() {
aoc2024::run_day("6", p1, p2);
}
|
