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| Original file line number | Diff line number | Diff line change |
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| use std::collections::VecDeque; | ||
|
|
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| use advent_of_code::Grid; | ||
| use itertools::Itertools; | ||
| use once_cell::sync::Lazy; | ||
| use rand::RngCore; | ||
| use strum::{Display, EnumIter, EnumString, FromRepr}; | ||
|
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| advent_of_code::solution!(21); | ||
|
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| /// The grid for part 1 is | ||
| /// +---+---+---+ | ||
| /// | 7 | 8 | 9 | | ||
| /// +---+---+---+ | ||
| /// | 4 | 5 | 6 | | ||
| /// +---+---+---+ | ||
| /// | 1 | 2 | 3 | | ||
| /// +---+---+---+ | ||
| /// |0/^| A | | ||
| /// +---+---+---+ | ||
| /// | < | v | > | | ||
| /// +---+---+---+ | ||
| /// 7 is at index 0 and index 9 is not accessible | ||
| const BUTTON_COUNT: usize = 15; | ||
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| static GRID: Lazy<Grid<Button>> = Lazy::new(|| { | ||
| Grid::new( | ||
| (0..BUTTON_COUNT) | ||
| .map(|i| Button::from_repr(i as u8).unwrap()) | ||
| .collect_vec(), | ||
| 3, | ||
| ) | ||
| }); | ||
|
|
||
| #[derive( | ||
| EnumString, | ||
| FromRepr, | ||
| Display, | ||
| Debug, | ||
| Clone, | ||
| Copy, | ||
| PartialEq, | ||
| Eq, | ||
| Default, | ||
| EnumIter, | ||
| Hash, | ||
| )] | ||
| #[repr(u8)] | ||
| enum Button { | ||
| Seven, | ||
| Eight, | ||
| Nine, | ||
| Four, | ||
| Five, | ||
| Six, | ||
| One, | ||
| Two, | ||
| Three, | ||
| None, | ||
| ZeroUp, | ||
| #[default] | ||
| A, | ||
| Left, | ||
| Down, | ||
| Right, | ||
| } | ||
|
|
||
| impl From<u8> for Button { | ||
| fn from(c: u8) -> Self { | ||
| match c { | ||
| b'0' => Button::ZeroUp, | ||
| b'1' => Button::One, | ||
| b'2' => Button::Two, | ||
| b'3' => Button::Three, | ||
| b'4' => Button::Four, | ||
| b'5' => Button::Five, | ||
| b'6' => Button::Six, | ||
| b'7' => Button::Seven, | ||
| b'8' => Button::Eight, | ||
| b'9' => Button::Nine, | ||
| b'A' => Button::A, | ||
| b'>' => Button::Right, | ||
| b'<' => Button::Left, | ||
| b'^' => Button::ZeroUp, | ||
| b'v' => Button::Down, | ||
| _ => unreachable!(), | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl Button { | ||
| fn same_class(b1: usize, b2: usize) -> bool { | ||
| matches!((b1, b2), (0..=8 | 10 | 11, 0..=8 | 10 | 11) | (10.., 10..)) | ||
| } | ||
| } | ||
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| type Path = Vec<Button>; | ||
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| fn seeded_all_paths(mut seed: u64) -> Vec<Path> { | ||
| (0..(BUTTON_COUNT.pow(2))) | ||
| .map(|i| (i / BUTTON_COUNT, i % BUTTON_COUNT)) | ||
| .map(|(start, end)| shortest_path(start, end, &mut seed)) | ||
| .collect_vec() | ||
| } | ||
|
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||
| fn count_changes(path: &Path) -> usize { | ||
| path.iter() | ||
| .fold((0, None), |(acc, prev), curr| { | ||
| if let Some(prev) = prev { | ||
| (acc + (curr != prev) as usize, Some(curr)) | ||
| } else { | ||
| (0, Some(curr)) | ||
| } | ||
| }) | ||
| .0 | ||
| } | ||
|
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| fn shortest_path(start: usize, end: usize, seed: &mut u64) -> Path { | ||
| let mut result = vec![]; | ||
|
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| if !Button::same_class(start, end) { | ||
| return vec![]; | ||
| } | ||
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| let mut queue = [(start, 1 << start, Path::default(), 0)] | ||
| .into_iter() | ||
| .collect::<VecDeque<_>>(); | ||
| let mut shortest_opt = None; | ||
|
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| while let Some((curr, seen, path, dist)) = queue.pop_front() { | ||
| if curr == end { | ||
| if let Some(shortest) = shortest_opt { | ||
| if shortest < dist { | ||
| break; | ||
| } | ||
| } else { | ||
| shortest_opt = Some(dist); | ||
| } | ||
|
|
||
| if count_changes(&path) < 2 { | ||
| result.push(path); | ||
| } | ||
| continue; | ||
| } | ||
|
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||
| queue.extend( | ||
| GRID.neighbors(curr) | ||
| .filter(|(_, n)| GRID.data[*n] != Button::None) | ||
| .map(|(d, n)| (d, n, (1 << n) | seen)) | ||
| .filter(|(_, _, n_seen)| *n_seen != seen) | ||
| .map(|(d, n, n_seen)| { | ||
| let mut n_path = path.clone(); | ||
|
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| n_path.push(d.to_arrow().into()); | ||
| (n, n_seen, n_path, dist + 1) | ||
| }), | ||
| ); | ||
| } | ||
|
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| result.iter_mut().for_each(|p| p.push(Button::A)); | ||
|
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| if result.len() > 1 { | ||
| *seed /= 2; | ||
| if *seed % 2 == 1 { | ||
| result.into_iter().nth(1).unwrap() | ||
| } else { | ||
| result.into_iter().next().unwrap() | ||
| } | ||
| } else { | ||
| result.into_iter().next().unwrap() | ||
| } | ||
| } | ||
|
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| fn parse_buttons(line: &str) -> (usize, [Button; 4]) { | ||
| let value: usize = line[..3].parse().unwrap(); | ||
|
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| let mut result = [Button::A; 4]; | ||
|
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| result | ||
| .iter_mut() | ||
| .take(3) | ||
| .enumerate() | ||
| .for_each(|(i, t)| *t = line.as_bytes()[i].into()); | ||
|
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| (value, result) | ||
| } | ||
|
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| fn fast_single_answer( | ||
| buttons: &[Button], | ||
| iterations: usize, | ||
| all_paths: &[Path], | ||
| ) -> usize { | ||
| let mut pairs = vec![0; BUTTON_COUNT * BUTTON_COUNT]; | ||
|
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| let pair_contributions = all_paths | ||
| .iter() | ||
| .map(|path| { | ||
| if path.is_empty() { | ||
| vec![] | ||
| } else { | ||
| Some(Button::A) | ||
| .into_iter() | ||
| .chain(path.iter().copied()) | ||
| .tuple_windows::<(_, _)>() | ||
| .map(|(f, t)| f as usize * BUTTON_COUNT + t as usize) | ||
| .collect_vec() | ||
| } | ||
| }) | ||
| .collect_vec(); | ||
|
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| Some(Button::A) | ||
| .into_iter() | ||
| .chain(buttons.iter().copied()) | ||
| .tuple_windows::<(_, _)>() | ||
| .map(|(f, t)| f as usize * BUTTON_COUNT + t as usize) | ||
| .for_each(|i| pairs[i] += 1); | ||
|
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| for _ in 0..iterations { | ||
| let mut new_pairs = vec![0; BUTTON_COUNT * BUTTON_COUNT]; | ||
|
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| pairs.drain(..).enumerate().for_each(|(i, count)| { | ||
| pair_contributions[i] | ||
| .iter() | ||
| .for_each(|j| new_pairs[*j] += count) | ||
| }); | ||
|
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| pairs.append(&mut new_pairs); | ||
| } | ||
|
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| pairs.into_iter().sum() | ||
| } | ||
|
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| pub fn part_one(input: &str) -> Option<usize> { | ||
| let all_paths = seeded_all_paths(u64::MAX); | ||
| let result = input | ||
| .lines() | ||
| .map(parse_buttons) | ||
| .map(|(value, buttons)| { | ||
| fast_single_answer(&buttons, 3, &all_paths) * value | ||
| }) | ||
| .sum(); | ||
|
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| Some(result) | ||
| } | ||
|
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| pub fn part_two(input: &str) -> Option<usize> { | ||
| (0..1000) | ||
| .map(|_| { | ||
| let seed = rand::thread_rng().next_u64(); | ||
| let all_paths = seeded_all_paths(seed); | ||
|
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| input | ||
| .lines() | ||
| .map(parse_buttons) | ||
| .map(|(value, buttons)| { | ||
| value * fast_single_answer(&buttons, 26, &all_paths) | ||
| }) | ||
| .sum() | ||
| }) | ||
| .min() | ||
| } | ||
|
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| #[cfg(test)] | ||
| mod tests { | ||
| use super::*; | ||
|
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| #[test] | ||
| fn test_part_one() { | ||
| let result = | ||
| part_one(&advent_of_code::template::read_file("examples", DAY)); | ||
| assert_eq!(result, Some(126384)); | ||
| } | ||
|
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| #[test] | ||
| fn test_part_two() { | ||
| let result = | ||
| part_two(&advent_of_code::template::read_file("examples", DAY)); | ||
| assert_eq!(result, Some(154115708116294)); | ||
| } | ||
| } |
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