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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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