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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,277 @@ | ||
| use std::cmp::min; | ||
| use std::collections::BTreeMap; | ||
|
|
||
| #[derive(Clone, Copy, Debug)] | ||
| enum Move { | ||
| Steps(usize), | ||
| Left, | ||
| Right, | ||
| } | ||
|
|
||
| fn parse<'a, I, S>(lines: I) -> Option<(Vec<&'a [u8]>, Vec<Move>)> | ||
| where | ||
| I: IntoIterator<Item = &'a S>, | ||
| S: AsRef<str> + 'a, | ||
| { | ||
| let mut iter = lines.into_iter(); | ||
| let mut board = vec![]; | ||
| for line in iter.by_ref() { | ||
| let line = line.as_ref(); | ||
| if line.is_empty() { | ||
| break; | ||
| } | ||
| board.push(line.as_bytes()); | ||
| } | ||
| let mut moves = vec![]; | ||
| let mut line = iter.next()?.as_ref(); | ||
| while !line.is_empty() { | ||
| if let Some(tail) = line.strip_prefix('L') { | ||
| moves.push(Move::Left); | ||
| line = tail; | ||
| } else if let Some(tail) = line.strip_prefix('R') { | ||
| moves.push(Move::Right); | ||
| line = tail; | ||
| } else { | ||
| let (digits, tail) = line.split_at( | ||
| line.find(|c: char| !c.is_ascii_digit()) | ||
| .unwrap_or(line.len()), | ||
| ); | ||
| moves.push(Move::Steps(digits.parse().ok()?)); | ||
| line = tail; | ||
| } | ||
| } | ||
| Some((board, moves)) | ||
| } | ||
|
|
||
| struct Perimeter<'a> { | ||
| board: &'a [&'a [u8]], | ||
| initial: (usize, usize, u8), | ||
| next: Option<(usize, usize, u8)>, | ||
| } | ||
| fn perimeter<'a>(board: &'a [&'a [u8]]) -> Option<Perimeter<'a>> { | ||
| let initial = ( | ||
| board | ||
| .first()? | ||
| .iter() | ||
| .enumerate() | ||
| .find(|(_, &b)| b == b'.')? | ||
| .0, | ||
| 0, | ||
| 0, | ||
| ); | ||
| Some(Perimeter { | ||
| board, | ||
| initial, | ||
| next: Some(initial), | ||
| }) | ||
| } | ||
| impl<'a> Iterator for Perimeter<'a> { | ||
| type Item = (usize, usize, u8); | ||
| fn next(&mut self) -> Option<Self::Item> { | ||
| let current @ (x, y, d) = self.next?; | ||
| let forward = match d { | ||
| 0 => Some((x + 1, y)), | ||
| 1 => Some((x, y + 1)), | ||
| 2 => x.checked_sub(1).map(|x| (x, y)), | ||
| 3 => y.checked_sub(1).map(|y| (x, y)), | ||
| _ => unreachable!(), | ||
| }; | ||
| self.next = if forward | ||
| .and_then(|(x, y)| Some(*self.board.get(y)?.get(x)?)) | ||
| .unwrap_or(b' ') | ||
| == b' ' | ||
| { | ||
| Some((x, y, (d + 1) % 4)) | ||
| } else { | ||
| let left = match d { | ||
| 0 => y.checked_sub(1).map(|y| (x + 1, y)), | ||
| 1 => Some((x + 1, y + 1)), | ||
| 2 => x.checked_sub(1).map(|x| (x, y + 1)), | ||
| 3 => x.checked_sub(1).zip(y.checked_sub(1)), | ||
| _ => unreachable!(), | ||
| }; | ||
| if left | ||
| .and_then(|(x, y)| Some(*self.board.get(y)?.get(x)?)) | ||
| .unwrap_or(b' ') | ||
| == b' ' | ||
| { | ||
| forward.map(|(x, y)| (x, y, d)) | ||
| } else { | ||
| left.map(|(x, y)| (x, y, (d + 3) % 4)) | ||
| } | ||
| } | ||
| .filter(|state| state != &self.initial); | ||
| Some(current) | ||
| } | ||
| } | ||
|
|
||
| fn run( | ||
| board: &[&[u8]], | ||
| moves: &[Move], | ||
| warps: &BTreeMap<(usize, usize, u8), (usize, usize, u8)>, | ||
| ) -> Option<usize> { | ||
| let (x, y, d) = moves.iter().fold( | ||
| ( | ||
| board | ||
| .first()? | ||
| .iter() | ||
| .enumerate() | ||
| .find(|(_, &b)| b == b'.')? | ||
| .0, | ||
| 0, | ||
| 0u8, | ||
| ), | ||
| |(x, y, d), &r#move| match r#move { | ||
| Move::Steps(n) => { | ||
| let mut pos = (x, y, d); | ||
| for _ in 0..n { | ||
| let Some(next) = warps | ||
| .get(&pos) | ||
| .copied() | ||
| .or_else(|| { | ||
| match pos.2 { | ||
| 0 => Some((pos.0 + 1, pos.1, pos.2)), | ||
| 1 => Some((pos.0, pos.1 + 1, pos.2)), | ||
| 2 => pos.0.checked_sub(1).map(|x| (x, pos.1, pos.2)), | ||
| 3 => pos.1.checked_sub(1).map(|y| (pos.0, y, pos.2)), | ||
| _ => unreachable!(), | ||
| } | ||
| }) | ||
| .filter(|&(x, y, _)| { | ||
| board.get(y).and_then(|line| line.get(x)) == Some(&b'.') | ||
| }) | ||
| else { return pos }; | ||
| pos = next; | ||
| } | ||
| pos | ||
| } | ||
| Move::Left => (x, y, (d + 3) % 4), | ||
| Move::Right => (x, y, (d + 1) % 4), | ||
| }, | ||
| ); | ||
| Some(1000 * (y + 1) + 4 * (x + 1) + d as usize) | ||
| } | ||
|
|
||
| pub fn part1<'a, I, S>(lines: I) -> Option<usize> | ||
| where | ||
| I: IntoIterator<Item = &'a S>, | ||
| S: AsRef<str> + 'a, | ||
| { | ||
| let (board, moves) = parse(lines)?; | ||
| let warps = perimeter(&board)? | ||
| .map(|(x, y, d)| match d { | ||
| 0 => board | ||
| .iter() | ||
| .enumerate() | ||
| .rev() | ||
| .find(|(_, &line)| line.get(x).filter(|&&b| b != b' ').is_some()) | ||
| .map(|(y2, _)| ((x, y, 3), (x, y2, 3))), | ||
| 1 => board.get(y).and_then(|&line| { | ||
| line.iter() | ||
| .enumerate() | ||
| .find(|(_, &b)| b != b' ') | ||
| .map(|(x2, _)| ((x, y, 0), (x2, y, 0))) | ||
| }), | ||
| 2 => board | ||
| .iter() | ||
| .enumerate() | ||
| .find(|(_, &line)| line.get(x).filter(|&&b| b != b' ').is_some()) | ||
| .map(|(y2, _)| ((x, y, 1), (x, y2, 1))), | ||
| 3 => board.get(y).and_then(|&line| { | ||
| line.iter() | ||
| .enumerate() | ||
| .rev() | ||
| .find(|(_, &b)| b != b' ') | ||
| .map(|(x2, _)| ((x, y, 2), (x2, y, 2))) | ||
| }), | ||
| _ => unreachable!(), | ||
| }) | ||
| .collect::<Option<_>>()?; | ||
| run(&board, &moves, &warps) | ||
| } | ||
|
|
||
| pub fn part2<'a, I, S>(lines: I) -> Option<usize> | ||
| where | ||
| I: IntoIterator<Item = &'a S>, | ||
| S: AsRef<str> + 'a, | ||
| { | ||
| let (board, moves) = parse(lines)?; | ||
| let perimeter = perimeter(&board)?.collect::<Vec<_>>(); | ||
| let side_length = perimeter | ||
| .iter() | ||
| .map(|&(_, _, d)| Some(d)) | ||
| .chain(None) | ||
| .fold((Some(0), 0, usize::MAX), |(prev, count, size), cur| { | ||
| if prev == cur { | ||
| (cur, count + 1, size) | ||
| } else { | ||
| (cur, 1, min(size, count)) | ||
| } | ||
| }) | ||
| .2; | ||
| let mut unpaired_edges = perimeter | ||
| .iter() | ||
| .enumerate() | ||
| .step_by(side_length) | ||
| .map(|(i, &(_, _, d))| (i, d)) | ||
| .collect::<Vec<_>>(); | ||
| let mut paired_edges = vec![]; | ||
| while !unpaired_edges.is_empty() { | ||
| let mut i = 0; | ||
| while i + 1 < unpaired_edges.len() { | ||
| if unpaired_edges[i].1 == (unpaired_edges[i + 1].1 + 1) % 4 { | ||
| paired_edges.push((unpaired_edges[i].0, unpaired_edges[i + 1].0)); | ||
| unpaired_edges.drain(i..i + 2); | ||
| for (_, d) in &mut unpaired_edges[i..] { | ||
| *d = (*d + 3) % 4; | ||
| } | ||
| } else { | ||
| i += 1; | ||
| } | ||
| } | ||
| } | ||
| let mut warps = BTreeMap::new(); | ||
| for (i, j) in paired_edges { | ||
| for (&(x1, y1, d1), &(x2, y2, d2)) in perimeter[i..i + side_length] | ||
| .iter() | ||
| .zip(perimeter[j..j + side_length].iter().rev()) | ||
| { | ||
| warps.insert((x1, y1, (d1 + 3) % 4), (x2, y2, (d2 + 1) % 4)); | ||
| warps.insert((x2, y2, (d2 + 3) % 4), (x1, y1, (d1 + 1) % 4)); | ||
| } | ||
| } | ||
| run(&board, &moves, &warps) | ||
| } | ||
|
|
||
| #[cfg(test)] | ||
| mod tests { | ||
| use super::*; | ||
| use pretty_assertions::assert_eq; | ||
|
|
||
| static EXAMPLE: &[&str] = &[ | ||
| " ...#", | ||
| " .#..", | ||
| " #...", | ||
| " ....", | ||
| "...#.......#", | ||
| "........#...", | ||
| "..#....#....", | ||
| "..........#.", | ||
| " ...#....", | ||
| " .....#..", | ||
| " .#......", | ||
| " ......#.", | ||
| "", | ||
| "10R5L5R10L4R5L5", | ||
| ]; | ||
|
|
||
| #[test] | ||
| fn part1_examples() { | ||
| assert_eq!(Some(6032), part1(EXAMPLE)); | ||
| } | ||
|
|
||
| #[test] | ||
| fn part2_examples() { | ||
| assert_eq!(Some(5031), part2(EXAMPLE)); | ||
| } | ||
| } |
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