Created
December 17, 2020 13:30
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use std::collections::{HashMap, HashSet}; | |
use std::convert::Into; | |
use std::fs; | |
use std::io; | |
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)] | |
struct Point { | |
d: [i64; 4], | |
} | |
#[derive(Clone, Copy)] | |
enum Dimensions { | |
Three, | |
Four, | |
} | |
struct Neighbors { | |
base: [i64; 4], | |
submask: u32, | |
mask: u32, | |
} | |
fn has_0b11(submask: u32) -> bool { | |
for i in 0 as u32..4 { | |
if (submask >> (2 * i)) & 0b11 == 0b11 { | |
return true; | |
} | |
} | |
false | |
} | |
const SHIFTS: [i64; 3] = [0, -1, 1]; | |
impl Iterator for Neighbors { | |
type Item = Point; | |
fn next(&mut self) -> Option<Point> { | |
while has_0b11(self.submask) { | |
self.submask = (self.submask - 1) & self.mask; | |
} | |
match self.submask { | |
0 => None, | |
_ => { | |
let mut d = self.base.clone(); | |
for i in 0u32..4 { | |
d[i as usize] += SHIFTS[((self.submask >> (2 * i)) & 0b11) as usize]; | |
} | |
self.submask = (self.submask - 1) & self.mask; | |
Some(Point { d: d }) | |
} | |
} | |
} | |
} | |
impl Point { | |
fn neighbors(&self, dimensions: Dimensions) -> Neighbors { | |
let mask: u32 = match dimensions { | |
Dimensions::Three => 0b00111111, | |
Dimensions::Four => 0b11111111, | |
}; | |
Neighbors { | |
base: self.d.clone(), | |
submask: mask, | |
mask: mask, | |
} | |
} | |
} | |
#[derive(Debug, Clone)] | |
struct Cubes { | |
active: HashSet<Point>, | |
} | |
impl Into<Cubes> for String { | |
fn into(self) -> Cubes { | |
Cubes { | |
active: self | |
.lines() | |
.enumerate() | |
.flat_map(|(y, line)| { | |
line.bytes() | |
.enumerate() | |
.filter_map(move |(x, cell)| match cell { | |
b'#' => Some(Point { | |
d: [x as i64, y as i64, 0, 0], | |
}), | |
_ => None, | |
}) | |
}) | |
.collect(), | |
} | |
} | |
} | |
fn transition(cubes: &Cubes, dimensions: Dimensions) -> Cubes { | |
let mut to_active = HashSet::new(); | |
let mut inactive_neighbors: HashMap<Point, usize> = HashMap::new(); | |
for cube in cubes.active.iter().copied() { | |
let mut active_neighbors = 0usize; | |
for neighbor in cube.neighbors(dimensions) { | |
if cubes.active.contains(&neighbor) { | |
active_neighbors += 1; | |
} else { | |
*inactive_neighbors.entry(neighbor).or_insert(0) += 1; | |
} | |
} | |
if (2usize..=3).contains(&active_neighbors) { | |
to_active.insert(cube); | |
} | |
} | |
for (cube, count) in inactive_neighbors { | |
if count == 3 { | |
to_active.insert(cube); | |
} | |
} | |
Cubes { active: to_active } | |
} | |
fn run_transitions<T>(init: T, count: usize, dimensions: Dimensions) -> Cubes | |
where | |
T: Into<Cubes>, | |
{ | |
(0..count) | |
.into_iter() | |
.fold(init.into(), |result, _| transition(&result, dimensions)) | |
} | |
#[test] | |
fn test_run_transitions() { | |
assert_eq!( | |
112, | |
run_transitions( | |
" | |
.#. | |
..# | |
### | |
" | |
.to_string(), | |
6, | |
Dimensions::Three, | |
) | |
.active | |
.len() | |
); | |
} | |
#[allow(dead_code)] | |
pub fn solve_p1(input: &str) -> io::Result<usize> { | |
Ok( | |
run_transitions(fs::read_to_string(input)?.to_string(), 6, Dimensions::Three) | |
.active | |
.len(), | |
) | |
} | |
#[allow(dead_code)] | |
pub fn solve_p2(input: &str) -> io::Result<usize> { | |
Ok( | |
run_transitions(fs::read_to_string(input)?.to_string(), 6, Dimensions::Four) | |
.active | |
.len(), | |
) | |
} |
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