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ictrobotictrobot
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2024 day 15
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‎crates/utils/src/grid.rs‎

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@@ -142,3 +142,35 @@ pub fn from_str_padded<T: Clone>(
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Ok((rows, padded_columns, data))
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}
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/// Checks that the provided grid has walls on each edge.
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///
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/// # Examples
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/// ```
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/// # use utils::grid::is_enclosed;
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/// assert_eq!(
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/// is_enclosed(5, 6, &[
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/// b'#', b'#', b'#', b'#', b'#', b'#',
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/// b'#', b'.', b'.', b'.', b'.', b'#',
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/// b'#', b'.', b'.', b'.', b'.', b'#',
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/// b'#', b'.', b'.', b'.', b'.', b'#',
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/// b'#', b'#', b'#', b'#', b'#', b'#',
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/// ], |&b| b == b'#'),
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/// true,
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/// );
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/// assert_eq!(
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/// is_enclosed(5, 6, &[
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/// b'#', b'#', b'#', b'#', b'#', b'#',
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/// b'#', b'.', b'.', b'.', b'.', b'#',
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/// b'#', b'.', b'.', b'.', b'.', b'#',
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/// b'#', b'.', b'.', b'.', b'.', b'.',
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/// b'#', b'#', b'#', b'#', b'#', b'#',
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/// ], |&b| b == b'#'),
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/// false,
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/// );
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/// ```
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pub fn is_enclosed<T>(rows: usize, cols: usize, grid: &[T], is_wall: impl Fn(&T) -> bool) -> bool {
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grid[..cols].iter().all(&is_wall)
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&& grid[(rows - 1) * cols..].iter().all(&is_wall)
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&& (1..rows).all(|r| is_wall(&grid[r * cols]) && is_wall(&grid[(r + 1) * cols - 1]))
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}

‎crates/year2024/examples/day15_example0.txt‎

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##########
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#..O..O.O#
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#......O.#
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#.OO..O.O#
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#[email protected].#
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#O#..O...#
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#O..O..O.#
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#.OO.O.OO#
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#....O...#
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##########
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<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
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vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
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><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
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<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
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^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
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^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
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>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
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<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
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^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
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v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^

‎crates/year2024/examples/day15_example1.txt‎

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########
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#..O.O.#
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##@.O..#
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#...O..#
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#.#.O..#
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#...O..#
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#......#
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########
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<^^>>>vv<v>>v<<

‎crates/year2024/examples/day15_example2.txt‎

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#######
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#...#.#
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#.....#
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#..OO@#
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#..O..#
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#.....#
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#######
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<vv<<^^<<^^

‎crates/year2024/src/day15.rs‎

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use utils::grid;
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use utils::prelude::*;
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/// Moving boxes around a grid.
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#[derive(Clone, Debug)]
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pub struct Day15<'a> {
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cols: usize,
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grid: Vec<u8>,
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robot: usize,
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moves: &'a str,
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}
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impl<'a> Day15<'a> {
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pub fn new(input: &'a str, _: InputType) -> Result<Self, InputError> {
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let Some((grid, moves)) = input.split_once("\n\n") else {
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return Err(InputError::new(input, 0, "expected grid and moves"));
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};
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let (rows, cols, mut grid) = grid::from_str(grid, |b| match b {
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b'.' | b'#' | b'O' | b'@' => Some(b),
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_ => None,
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})?;
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if !grid::is_enclosed(rows, cols, &grid, |&b| b == b'#') {
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return Err(InputError::new(
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input,
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0,
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"expected grid to be enclosed by walls",
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));
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}
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let mut robots = grid.iter().enumerate().filter(|(_, &b)| b == b'@');
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let Some((robot, _)) = robots.next() else {
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return Err(InputError::new(input, 0, "expected a robot"));
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};
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if robots.count() > 0 {
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return Err(InputError::new(input, 0, "expected only one robot"));
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}
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grid[robot] = b'.';
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if let Some(idx) = moves.find(|b| !matches!(b, '^' | 'v' | '<' | '>' | '\n')) {
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return Err(InputError::new(
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input,
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&moves[idx..],
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"expected ^, v, <, or >",
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));
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}
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Ok(Self {
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cols,
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grid,
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robot,
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moves,
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})
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}
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#[must_use]
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pub fn part1(&self) -> u32 {
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let mut grid = self.grid.clone();
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let mut robot = self.robot;
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for offset in self.moves_iterator(self.cols) {
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let next = robot.wrapping_add_signed(offset);
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if grid[next] == b'.' {
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robot = next;
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} else if grid[next] == b'O' {
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let mut next_free = next.wrapping_add_signed(offset);
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while grid[next_free] == b'O' {
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next_free = next_free.wrapping_add_signed(offset);
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}
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if grid[next_free] == b'.' {
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grid[next_free] = b'O';
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grid[next] = b'.';
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robot = next;
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}
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}
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}
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Self::sum_box_coords(&grid, self.cols, b'O')
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}
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#[must_use]
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pub fn part2(&self) -> u32 {
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let mut grid = self
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.grid
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.iter()
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.flat_map(|&b| match b {
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b'#' => [b'#', b'#'],
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b'.' => [b'.', b'.'],
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b'O' => [b'[', b']'],
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_ => unreachable!(),
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})
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.collect::<Vec<_>>();
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let cols = self.cols * 2;
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let mut robot = (self.robot / self.cols * cols) + (self.robot % self.cols * 2);
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for offset in self.moves_iterator(cols) {
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let next = robot.wrapping_add_signed(offset);
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if grid[next] == b'.' {
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robot = next;
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} else if (grid[next] == b'[' || grid[next] == b']')
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&& Self::can_move_p2(&grid, next, offset)
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{
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Self::move_box_p2(&mut grid, next, offset);
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robot = next;
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}
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}
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Self::sum_box_coords(&grid, cols, b'[')
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}
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#[inline]
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fn moves_iterator(&self, cols: usize) -> impl Iterator<Item = isize> + use<'_> {
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self.moves.bytes().filter_map(move |c| match c {
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b'^' => Some(-(cols as isize)),
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b'v' => Some(cols as isize),
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b'<' => Some(-1),
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b'>' => Some(1),
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_ => None,
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})
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}
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#[inline]
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fn sum_box_coords(grid: &[u8], cols: usize, box_byte: u8) -> u32 {
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grid.iter()
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.enumerate()
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.map(|(i, &b)| {
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if b == box_byte {
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100 * ((i / cols) as u32) + ((i % cols) as u32)
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} else {
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0
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}
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})
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.sum()
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}
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fn can_move_p2(grid: &[u8], pos: usize, offset: isize) -> bool {
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let (left, right) = match grid[pos] {
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b'[' => (pos, pos + 1),
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b']' => (pos - 1, pos),
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b'.' => return true,
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b'#' => return false,
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_ => unreachable!(),
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};
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if offset == -1 || offset == 1 {
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Self::can_move_p2(grid, pos.wrapping_add_signed(offset), offset)
147+
} else if grid[left.wrapping_add_signed(offset)] == b'[' {
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// One box directly above/below, only need to recurse once
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Self::can_move_p2(grid, left.wrapping_add_signed(offset), offset)
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} else {
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Self::can_move_p2(grid, left.wrapping_add_signed(offset), offset)
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&& Self::can_move_p2(grid, right.wrapping_add_signed(offset), offset)
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}
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}
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fn move_box_p2(grid: &mut [u8], pos: usize, offset: isize) {
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let (left, right) = match grid[pos] {
158+
b'[' => (pos, pos + 1),
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b']' => (pos - 1, pos),
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b'.' => return,
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_ => unreachable!(),
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};
163+
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if offset == -1 || offset == 1 {
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Self::move_box_p2(grid, pos.wrapping_add_signed(offset * 2), offset);
166+
} else {
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Self::move_box_p2(grid, left.wrapping_add_signed(offset), offset);
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Self::move_box_p2(grid, right.wrapping_add_signed(offset), offset);
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}
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grid[left] = b'.';
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grid[right] = b'.';
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grid[left.wrapping_add_signed(offset)] = b'[';
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grid[right.wrapping_add_signed(offset)] = b']';
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}
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}
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examples!(Day15<'_> -> (u32, u32) [
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{file: "day15_example0.txt", part1: 10092, part2: 9021},
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{file: "day15_example1.txt", part1: 2028},
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{file: "day15_example2.txt", part2: 618},
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]);

‎crates/year2024/src/lib.rs‎

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@@ -16,4 +16,5 @@ utils::year!(2024 => year2024, ${
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12 => day12::Day12,
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13 => day13::Day13,
1818
14 => day14::Day14,
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15 => day15::Day15<'_>,
1920
});

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