I decided to split the movement instructions lines further for aesthetic reasons when opening it in the online uiua pad since newlines are thrown out anyways.

$ ##########
$ #..O..O.O#
$ #......O.#
$ #.OO..O.O#
$ #..O@..O.#
$ #O#..O...#
$ #O..O..O.#
$ #.OO.O.OO#
$ #....O...#
$ ##########
$ 
$ <vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><
$ <><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
$ vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<
$ >><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
$ ><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v
$ ^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
$ <<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^
$ <vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
$ ^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>
$ >^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
$ ^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><
$ <<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
$ >^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv
$ <<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
$ <><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><
$ <><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
$ ^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^
$ >vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
$ v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v>
$ <^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^

Pos ← :°⊟♭⊚⊸⌕@@
Move ← (
  ⊸⊗@.
  ⍣(+₁⍤.◡(≠⊙⧻)
    ⍜↙⍣(⬚@.↻₋₁⍤.=⊃(⧻|⊗@#).)∘
  )⋅∘
)

PartOne ← (
  # &rs ∞ &fo "input-15.txt"
  ⊜□¬⦷"\n\n".
  ∩°□°⊟
  : ⊙(▽≠@\n.) ⊜∘≠@\n.
  ↘₄⊛⊂"^>v<"
  ⍢(⊃↘₁⊢
    ⊙(⟜(⨬(⍉|∘)◿₂)
      ⟜(⨬(⍜(↘⊙⊡)Move Pos
        | ⍜(⇌↙⊙⊡)Move +₁Pos
        )=₀◿₃)
      ⨬(⍉|∘)◿₂
    )
  | ≠0⧻)
  ◌
  /+≡/+×[100_1]⊚⌕@O
)

PartTwo ← (
  ""
)

&p "Day 15:"
&pf "Part 1: "
&p PartOne
&pf "Part 2: "
&p PartTwo

type
  Vec2 = tuple[x,y: int]
  Box = array[2, Vec2]
  Dir = enum
    U = "^"
    R = ">"
    D = "v"
    L = "<"

proc convertPart2(grid: seq[string]): seq[string] =
  for y in 0..grid.high:
    result.add ""
    for x in 0..grid[0].high:
      result[^1] &= (
        if grid[y][x] == 'O': "[]"
        elif grid[y][x] == '#': "##"
        else: "..")

proc shiftLeft(grid: var seq[string], col: int, range: HSlice[int,int]) =
  for i in range.a ..< range.b:
    grid[col][i] = grid[col][i+1]
  grid[col][range.b] = '.'

proc shiftRight(grid: var seq[string], col: int, range: HSlice[int,int]) =
  for i in countDown(range.b, range.a+1):
    grid[col][i] = grid[col][i-1]
  grid[col][range.a] = '.'

proc box(pos: Vec2, grid: seq[string]): array[2, Vec2] =
  if grid[pos.y][pos.x] == '[':
    [pos, (pos.x+1, pos.y)]
  else:
    [(pos.x-1, pos.y), pos]

proc step(grid: var seq[string], bot: var Vec2, dir: Dir) =
  var (x, y) = bot
  case dir
  of U:
    while (dec y; grid[y][x] != '#' and grid[y][x] != '.'): discard
    if grid[y][x] == '#': return
    if grid[bot.y-1][bot.x] == 'O': swap(grid[bot.y-1][bot.x], grid[y][x])
    dec bot.y
  of R:
    while (inc x; grid[y][x] != '#' and grid[y][x] != '.'): discard
    if grid[y][x] == '#': return
    if grid[bot.y][bot.x+1] == 'O': swap(grid[bot.y][bot.x+1], grid[y][x])
    inc bot.x
  of L:
    while (dec x; grid[y][x] != '#' and grid[y][x] != '.'): discard
    if grid[y][x] == '#': return
    if grid[bot.y][bot.x-1] == 'O': swap(grid[bot.y][bot.x-1], grid[y][x])
    dec bot.x
  of D:
    while (inc y; grid[y][x] != '#' and grid[y][x] != '.'): discard
    if grid[y][x] == '#': return
    if grid[bot.y+1][bot.x] == 'O': swap(grid[bot.y+1][bot.x], grid[y][x])
    inc bot.y

proc canMoveVert(box: Box, grid: seq[string], boxes: var HashSet[Box], dy: int): bool =
  boxes.incl box
  var left, right = false
  let (lbox, rbox) = (box[0], box[1])
  let lbigBox = box((lbox.x, lbox.y+dy), grid)
  let rbigBox = box((rbox.x, lbox.y+dy), grid)

  if grid[lbox.y+dy][lbox.x] == '#' or
     grid[rbox.y+dy][rbox.x] == '#': return false
  elif grid[lbox.y+dy][lbox.x] == '.': left = true
  else:
    left = canMoveVert(box((lbox.x,lbox.y+dy), grid), grid, boxes, dy)

  if grid[rbox.y+dy][rbox.x] == '.': right = true
  elif lbigBox == rbigBox: right = left
  else:
    right = canMoveVert(box((rbox.x, rbox.y+dy), grid), grid, boxes, dy)

  left and right

proc moveBoxes(grid: var seq[string], boxes: var HashSet[Box], d: Vec2) =
  for box in boxes:
    grid[box[0].y][box[0].x] = '.'
    grid[box[1].y][box[1].x] = '.'
  for box in boxes:
    grid[box[0].y+d.y][box[0].x+d.x] = '['
    grid[box[1].y+d.y][box[1].x+d.x] = ']'
  boxes.clear()

proc step2(grid: var seq[string], bot: var Vec2, dir: Dir) =
  case dir
  of U:
    if grid[bot.y-1][bot.x] == '#': return
    if grid[bot.y-1][bot.x] == '.': dec bot.y
    else:
      var boxes: HashSet[Box]
      if canMoveVert(box((x:bot.x, y:bot.y-1), grid), grid, boxes, -1):
        grid.moveBoxes(boxes, (0, -1))
        dec bot.y
  of R:
    var (x, y) = bot
    while (inc x; grid[y][x] != '#' and grid[y][x] != '.'): discard
    if grid[y][x] == '#': return
    if grid[bot.y][bot.x+1] == '[': grid.shiftRight(bot.y, bot.x+1..x)
    inc bot.x
  of L:
    var (x, y) = bot
    while (dec x; grid[y][x] != '#' and grid[y][x] != '.'): discard
    if grid[y][x] == '#': return
    if grid[bot.y][bot.x-1] == ']': grid.shiftLeft(bot.y, x..bot.x-1)
    dec bot.x
  of D:
    if grid[bot.y+1][bot.x] == '#': return
    if grid[bot.y+1][bot.x] == '.': inc bot.y
    else:
      var boxes: HashSet[Box]
      if canMoveVert(box((x:bot.x, y:bot.y+1), grid), grid, boxes, 1):
        grid.moveBoxes(boxes, (0, 1))
        inc bot.y


proc solve(input: string): AOCSolution[int, int] =
  let chunks = input.split("\n\n")
  var grid = chunks[0].splitLines()
  let movements = chunks[1].splitLines().join().join()

  var robot: Vec2
  for y in 0..grid.high:
    for x in 0..grid[0].high:
      if grid[y][x] == '@':
        grid[y][x] = '.'
        robot = (x,y)

  block p1:
    var grid = grid
    var robot = robot
    for m in movements:
      let dir = parseEnum[Dir]($m)
      step(grid, robot, dir)
    for y in 0..grid.high:
      for x in 0..grid[0].high:
        if grid[y][x] == 'O':
          result.part1 += 100 * y + x

  block p2:
    var grid = grid.convertPart2()
    var robot = (robot.x*2, robot.y)
    for m in movements:
      let dir = parseEnum[Dir]($m)
      step2(grid, robot, dir)
      #grid.inspect(robot)

    for y in 0..grid.high:
      for x in 0..grid[0].high:
        if grid[y][x] == '[':
          result.part2 += 100 * y + x

import fs from "fs";

type Point = {x: number, y: number};

enum Direction {
    UP = '^',
    DOWN = 'v',
    LEFT = '<',
    RIGHT = '>'
}

const input = fs.readFileSync("./15/input.txt", "utf-8").split(/[\r\n]{4,}/);
const warehouse: string[][] = input[0]
    .split(/[\r\n]+/)
    .map(row => row.split(""));
const movements: Direction[] = input[1]
    .split("")
    .map(char => char.trim())
    .filter(Boolean)
    .map(char => char as Direction);

// Part 1
console.info("Part 1: " + solve(warehouse, movements));

// Part 2
const secondWarehouse = warehouse.map(row => {
    const newRow: string[] = [];
    for (const char of row) {
        if (char === '#') { newRow.push('#', '#'); }
        else if (char === 'O') { newRow.push('[', ']'); }
        else if (char === '.') { newRow.push('.', '.'); }
        else { newRow.push('@', '.'); }
    }
    return newRow;
});
console.info("Part 2: " + solve(secondWarehouse, movements));

function solve(warehouse: string[][], movements: Direction[]): number {
    let _warehouse = warehouse.map(row => [...row]); // Take a copy to avoid modifying the original
    const robotLocation: Point = findStartLocation(_warehouse);

    for (const move of movements) {
        // Under some very specific circumstances in part 2, tryMove returns false, but the grid has already been modified
        // "Fix" the issue ba taking a copy so we can easily revert all changes made
        // Slow AF of course but rest of this code isn't optimized either, so...
        const copy = _warehouse.map(row => [...row]);
    
        if (tryMove(robotLocation, move, _warehouse)) {
            if (move === Direction.UP) { robotLocation.y--; }
            else if (move === Direction.DOWN) { robotLocation.y++; }
            else if (move === Direction.LEFT) { robotLocation.x--; }
            else { robotLocation.x++; }
        } else {
            _warehouse = copy; // Revert changes
        }
    }

    // GPS
    let result = 0;
    for (let y = 0; y < _warehouse.length; y++) {
        for (let x = 0; x < _warehouse[y].length; x++) {
            if (_warehouse[y][x] === "O" || _warehouse[y][x] === "[") {
                result += 100 * y + x;
            }
        }
    }
    return result;
}

function tryMove(from: Point, direction: Direction, warehouse: string[][], movingPair = false): boolean {
    const moveWhat = warehouse[from.y][from.x];
    if (moveWhat === "#") {
        return false;
    }

    let to: Point;
    switch (direction) {
        case Direction.UP: to = {x: from.x, y: from.y - 1}; break;
        case Direction.DOWN: to = {x: from.x, y: from.y + 1}; break;
        case Direction.LEFT: to = {x: from.x - 1, y: from.y}; break;
        case Direction.RIGHT: to = {x: from.x + 1, y: from.y}; break;
    }

    const allowMove = warehouse[to.y][to.x] === "."
        || (direction === Direction.UP && tryMove({x: from.x, y: from.y - 1}, direction, warehouse))
        || (direction === Direction.DOWN && tryMove({x: from.x, y: from.y + 1}, direction, warehouse))
        || (direction === Direction.LEFT && tryMove({x: from.x - 1, y: from.y}, direction, warehouse))
        || (direction === Direction.RIGHT && tryMove({x: from.x + 1, y: from.y}, direction, warehouse));

    if (allowMove) {
        // Part 1 logic handles horizontal movement of larger boxes just fine. Needs special handling for vertical movement
        if (!movingPair && (direction === Direction.UP || direction === Direction.DOWN)) {
            if (moveWhat === "[" && !tryMove({x: from.x + 1, y: from.y}, direction, warehouse, true)) {
                return false;
            }
            if (moveWhat === "]" && !tryMove({x: from.x - 1, y: from.y}, direction, warehouse, true)) {
                return false;
            }
        }

        // Make the move
        warehouse[to.y][to.x] = moveWhat;
        warehouse[from.y][from.x] = ".";
        return true;
    }
    return false;
}

function findStartLocation(warehouse: string[][]): Point {
    for (let y = 0; y < warehouse.length; y++) {
        for (let x = 0; x < warehouse[y].length; x++) {
            if (warehouse[y][x] === "@") {
                return {x,y};
            }
        }
    }

    throw new Error("Could not find start location!");
}

use euclid::{default::*, vec2};

// Common type for both parts. In part 1 all boxes are BoxL.
#[derive(Clone, Copy)]
enum Spot {
    Empty,
    BoxL,
    BoxR,
    Wall,
}

impl From<u8> for Spot {
    fn from(value: u8) -> Self {
        match value {
            b'.' | b'@' => Spot::Empty,
            b'O' => Spot::BoxL,
            b'#' => Spot::Wall,
            other => panic!("Invalid spot: {other}"),
        }
    }
}

fn parse(input: &str) -> (Vec<Vec<Spot>>, Point2D<i32>, Vec<Vector2D<i32>>) {
    let (field_s, moves_s) = input.split_once("\n\n").unwrap();
    let mut field = Vec::new();
    let mut robot = None;
    for (y, l) in field_s.lines().enumerate() {
        let mut row = Vec::new();
        for (x, b) in l.bytes().enumerate() {
            row.push(Spot::from(b));
            if b == b'@' {
                robot = Some(Point2D::new(x, y).to_i32())
            }
        }
        field.push(row);
    }

    let moves = moves_s
        .bytes()
        .filter(|b| *b != b'\n')
        .map(|b| match b {
            b'^' => vec2(0, -1),
            b'>' => vec2(1, 0),
            b'v' => vec2(0, 1),
            b'<' => vec2(-1, 0),
            other => panic!("Invalid move: {other}"),
        })
        .collect();
    (field, robot.unwrap(), moves)
}

fn gps(field: &[Vec<Spot>]) -> u32 {
    let mut sum = 0;
    for (y, row) in field.iter().enumerate() {
        for (x, s) in row.iter().enumerate() {
            if let Spot::BoxL = s {
                sum += x + 100 * y;
            }
        }
    }
    sum as u32
}

fn part1(input: String) {
    let (mut field, mut robot, moves) = parse(&input);
    for m in moves {
        let next = robot + m;
        match field[next.y as usize][next.x as usize] {
            Spot::Empty => robot = next, // Move into space
            Spot::BoxL => {
                let mut search = next + m;
                let can_move = loop {
                    match field[search.y as usize][search.x as usize] {
                        Spot::BoxL => {}
                        Spot::Wall => break false,
                        Spot::Empty => break true,
                        Spot::BoxR => unreachable!(),
                    }
                    search += m;
                };
                if can_move {
                    robot = next;
                    field[next.y as usize][next.x as usize] = Spot::Empty;
                    field[search.y as usize][search.x as usize] = Spot::BoxL;
                }
            }
            Spot::Wall => {} // Cannot move
            Spot::BoxR => unreachable!(),
        }
    }
    println!("{}", gps(&field));
}

// Transform part 1 field to wider part 2 field
fn widen(field: &[Vec<Spot>]) -> Vec<Vec<Spot>> {
    field
        .iter()
        .map(|row| {
            row.iter()
                .flat_map(|s| match s {
                    Spot::Empty => [Spot::Empty; 2],
                    Spot::Wall => [Spot::Wall; 2],
                    Spot::BoxL => [Spot::BoxL, Spot::BoxR],
                    Spot::BoxR => unreachable!(),
                })
                .collect()
        })
        .collect()
}

// Recursively find out whether or not the robot can move in direction `dir` from `start`.
fn can_move_rec(field: &[Vec<Spot>], start: Point2D<i32>, dir: Vector2D<i32>) -> bool {
    let next = start + dir;
    match field[next.y as usize][next.x as usize] {
        Spot::Empty => true,
        Spot::BoxL => can_move_rec(field, next, dir) && can_move_rec(field, next + vec2(1, 0), dir),
        Spot::BoxR => can_move_rec(field, next - vec2(1, 0), dir) && can_move_rec(field, next, dir),
        Spot::Wall => false,
    }
}

// Recursively execute a move for vertical directions into boxes.
fn do_move(field: &mut [Vec<Spot>], start: Point2D<i32>, dir: Vector2D<i32>) {
    let next = start + dir;
    match field[next.y as usize][next.x as usize] {
        Spot::Empty | Spot::Wall => {}
        Spot::BoxL => {
            do_move(field, next, dir);
            do_move(field, next + vec2(1, 0), dir);
            let move_to = next + dir;
            field[next.y as usize][next.x as usize] = Spot::Empty;
            field[next.y as usize][next.x as usize + 1] = Spot::Empty;
            field[move_to.y as usize][move_to.x as usize] = Spot::BoxL;
            field[move_to.y as usize][move_to.x as usize + 1] = Spot::BoxR;
        }
        Spot::BoxR => {
            do_move(field, next - vec2(1, 0), dir);
            do_move(field, next, dir);
            let move_to = next + dir;
            field[next.y as usize][next.x as usize - 1] = Spot::Empty;
            field[next.y as usize][next.x as usize] = Spot::Empty;
            field[move_to.y as usize][move_to.x as usize - 1] = Spot::BoxL;
            field[move_to.y as usize][move_to.x as usize] = Spot::BoxR;
        }
    }
}

fn part2(input: String) {
    let (field1, robot1, moves) = parse(&input);
    let mut field = widen(&field1);
    let mut robot = Point2D::new(robot1.x * 2, robot1.y);
    for m in moves {
        let next = robot + m;
        match field[next.y as usize][next.x as usize] {
            Spot::Empty => robot = next, // Move into space
            Spot::BoxL | Spot::BoxR if m.y == 0 => {
                let mut search = next + m;
                let can_move = loop {
                    match field[search.y as usize][search.x as usize] {
                        Spot::BoxL | Spot::BoxR => {}
                        Spot::Wall => break false,
                        Spot::Empty => break true,
                    }
                    search += m;
                };
                if can_move {
                    robot = next;
                    // Shift boxes by array remove/insert
                    field[next.y as usize].remove(search.x as usize);
                    field[next.y as usize].insert(next.x as usize, Spot::Empty);
                }
            }
            Spot::BoxL | Spot::BoxR => {
                if can_move_rec(&field, robot, m) {
                    do_move(&mut field, robot, m);
                    robot = next;
                }
            }
            Spot::Wall => {} // Cannot move
        }
    }
    println!("{}", gps(&field));
}

util::aoc_main!();

import Control.Monad
import Data.Bifunctor
import Data.List
import Data.Map (Map)
import Data.Map qualified as Map
import Data.Set (Set)
import Data.Set qualified as Set

type C = (Int, Int)

readInput :: String -> (Map C Char, [C])
readInput s =
  let (room, _ : moves) = break null $ lines s
   in ( Map.fromList [((i, j), c) | (i, l) <- zip [0 ..] room, (j, c) <- zip [0 ..] l],
        map dir $ concat moves
      )
  where
    dir '^' = (-1, 0)
    dir 'v' = (1, 0)
    dir '<' = (0, -1)
    dir '>' = (0, 1)

moveInto :: Int -> Set C -> C -> C -> Set C -> Maybe (Set C)
moveInto boxWidth walls (di, dj) = go
  where
    go (i, j) boxes
      | (i, j) `Set.member` walls = Nothing
      | Just j' <- find (\j' -> (i, j') `Set.member` boxes) $ map (j -) [0 .. boxWidth - 1] =
          Set.insert (i + di, j' + dj)
            <$> foldM
              (flip go)
              (Set.delete (i, j') boxes)
              [(i + di, j' + z + dj) | z <- [0 .. boxWidth - 1]]
      | otherwise = Just boxes

runMoves :: (Map C Char, [C]) -> Int -> Int
runMoves (room, moves) scale = score $ snd $ foldl' move (start, boxes) moves
  where
    room' = Map.mapKeysMonotonic (second (* scale)) room
    Just start = fst <$> find ((== '@') . snd) (Map.assocs room')
    walls =
      let ps = Map.keysSet $ Map.filter (== '#') room'
       in Set.unions [Set.mapMonotonic (second (+ z)) ps | z <- [0 .. scale - 1]]
    boxes = Map.keysSet $ Map.filter (== 'O') room'
    move (pos@(i, j), boxes) dir@(di, dj) =
      let pos' = (i + di, j + dj)
       in maybe (pos, boxes) (pos',) $ moveInto scale walls dir pos' boxes
    score = sum . map (\(i, j) -> i * 100 + j) . Set.elems

main = do
  input <- readInput <$> readFile "input15"
  mapM_ (print . runMoves input) [1, 2]

/// Advent of Code 2024, Day 15
/// Copyright 2024 by Alex Utter

use aocfetch;
use std::collections::HashSet;

type Rc = (usize, usize);
type Delta = (isize, isize);
type Moves = Vec<Delta>;

fn add(rc:&Rc, mv:&Delta) -> Rc {
    (rc.0.saturating_add_signed(mv.0),
     rc.1.saturating_add_signed(mv.1))
}

struct Warehouse {
    part2: bool,
    robot: Rc,
    boxes: HashSet<Rc>,
    walls: HashSet<Rc>,
}

impl Warehouse {
    fn new(input: &str, part2: bool) -> (Warehouse, Moves) {
        let mut init = Warehouse {
            part2: part2,
            robot: (0,0),
            boxes: HashSet::new(),
            walls: HashSet::new(),
        };
        let mut moves = Vec::new();
        for (r,line) in input.trim().lines().enumerate() {
            for (c,ch) in line.trim().chars().enumerate() {
                let c2 = if part2 {2*c} else {c};
                match ch {
                    '@' => {init.robot = (r,c2);},
                    'O' => {init.boxes.insert((r,c2));},
                    '#' => {init.walls.insert((r,c2));
                            if part2 {init.walls.insert((r,c2+1));}},
                    '^' => {moves.push((-1, 0));},
                    '>' => {moves.push(( 0, 1));},
                    'v' => {moves.push(( 1, 0));},
                    '<' => {moves.push(( 0,-1));},
                    _   => {},
                }
            }
        }
        return (init, moves);
    }

    fn gps(&self) -> usize {
        self.boxes.iter().map(|(r,c)| 100*r + c).sum()
    }

    fn get_box(&self, rc: &Rc) -> Option<Rc> {
        let ll = add(rc, &(0,-1));
        let rr = rc.clone();
        if self.part2 && self.boxes.contains(&ll) {
            return Some(ll);
        } else if self.boxes.contains(&rr) {
            return Some(rr);
        } else {
            return None;
        }
    }

    fn push(&mut self, mv: &Delta) -> bool {
        // Identify all boxes affected by this push.
        let mut boxes = HashSet::new();     // List of affected boxes
        let mut queue = Vec::new();         // Squares being pushed
        queue.push(add(&self.robot, mv));
        while let Some(rc) = queue.pop() {
            if let Some(bx) = self.get_box(&rc) {
                // Push all square(s) affected by this box.
                let left  = add(&bx, mv);
                let right = add(&left, &(0,1));
                boxes.insert(bx);
                if left != rc {queue.push(left);}
                if self.part2 && right != rc {queue.push(right);}
            } else if self.walls.contains(&rc) {
                // If we hit a wall, the move cannot be applied.
                return false;
            }
        }

        // Move successful, update the warehouse state.
        self.robot = add(&self.robot, mv);
        for bx in boxes.iter() {self.boxes.remove(bx);}
        for bx in boxes.iter() {self.boxes.insert(add(bx, mv));}
        return true;
    }
}

fn part1(input: &str) -> usize {
    let (mut state, moves) = Warehouse::new(input, false);
    for mv in moves.iter() {state.push(mv);}
    return state.gps();
}

fn part2(input: &str) -> usize {
    let (mut state, moves) = Warehouse::new(input, true);
    for mv in moves.iter() {state.push(mv);}
    return state.gps();
}

const EXAMPLE1: &'static str = "\
    ########
    #..O.O.#
    ##@.O..#
    #...O..#
    #.#.O..#
    #...O..#
    #......#
    ########

    <^^>>>vv<v>>v<<";

const EXAMPLE2: &'static str = "\
    ##########
    #..O..O.O#
    #......O.#
    #.OO..O.O#
    #..O@..O.#
    #O#..O...#
    #O..O..O.#
    #.OO.O.OO#
    #....O...#
    ##########

    <vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
    vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
    ><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
    <<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
    ^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
    ^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
    >^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
    <><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
    ^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
    v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^";

fn main() {
    // Fetch input from server.
    let input = aocfetch::get_data(2024, 15).unwrap();

    assert_eq!(part1(EXAMPLE1), 2028);
    assert_eq!(part1(EXAMPLE2), 10092);
    assert_eq!(part2(EXAMPLE2), 9021);

    println!("Part 1: {}", part1(&input));
    println!("Part 2: {}", part2(&input));
}

import Control.Monad.State.Lazy
import qualified Data.Map.Strict as M

type Coord = (Int, Int)
data Block = Box | Wall
type Grid = M.Map Coord Block

parse :: String -> ((Coord, Grid), [Coord])
parse s =
    let robot = head
            [ (r, c)
            | (r, row) <- zip [0 ..] $ lines s
            , (c, '@') <- zip [0 ..] row
            ]
        grid = M.fromAscList
            [ ((r, c), val)
            | (r, row) <- zip [0 ..] $ lines s
            , (c, Just val) <- zip [0 ..] $ map f row
            ]
    in  ((robot, grid), go s)
    where
        f 'O' = Just Box
        f '#' = Just Wall
        f _ = Nothing
        go ('^' : rest) = (-1,  0) : go rest
        go ('v' : rest) = ( 1,  0) : go rest
        go ('<' : rest) = ( 0, -1) : go rest
        go ('>' : rest) = ( 0,  1) : go rest
        go (_   : rest) =            go rest
        go [] = []

add :: Coord -> Coord -> Coord
add (r0, c0) (r1, c1) = (r0 + r1, c0 + c1)

moveBoxes :: Coord -> Coord -> Grid -> Maybe Grid
moveBoxes dr r grid = case grid M.!? r of
    Nothing   -> Just grid
    Just Wall -> Nothing
    Just Box  ->
        M.insert (add r dr) Box . M.delete r <$> moveBoxes dr (add r dr) grid

move :: Coord -> State (Coord, Grid) Bool
move dr = state $ \(r, g) -> case moveBoxes dr (add r dr) g of
    Just g' -> (True, (add r dr, g'))
    Nothing -> (False, (r, g))

moves :: [Coord] -> State (Coord, Grid) ()
moves = mapM_ move

main :: IO ()
main = do
    ((robot, grid), movements) <- parse <$> getContents
    let (_, grid') = execState (moves movements) (robot, grid)
    print $ sum [100 * r + c | ((r, c), Box) <- M.toList grid']

#include "common.h"

#define GW 104
#define GH 52

struct world { char g[GH][GW]; int px,py; };

static int
can_clear(struct world *w, int x, int y, int dx, int dy)
{
	assert(x>=0); assert(x<GW);
	assert(y>=0); assert(y<GH);
	assert((dx && !dy) || (dy && !dx));

	return
	    (x+dx >= 0 || x+dx < GW) &&
	    (y+dy >= 0 || y+dy < GW) &&
	    (w->g[y][x] == '.' || (
	     w->g[y][x] != '#' && can_clear(w, x+dx,y+dy, dx,dy) &&
	     (!dy || w->g[y][x]!='[' || can_clear(w, x+1,y+dy, 0,dy)) &&
	     (!dy || w->g[y][x]!=']' || can_clear(w, x-1,y,    0,dy)) &&
	     (!dy || w->g[y][x]!=']' || can_clear(w, x-1,y+dy, 0,dy))));
}

/* check can_clear() first! */
static void
clear(struct world *w, int x, int y, int dx, int dy)
{
	assert(x>=0); assert(x<GW); assert(x+dx>=0); assert(x+dx<GW);
	assert(y>=0); assert(y<GH); assert(y+dy>=0); assert(y+dy<GH);

	if (w->g[y][x] == '.')
		return;
	if (dy && w->g[y][x] == ']')
		{ clear(w, x-1,y, dx,dy); return; }

	if (dy && w->g[y][x] == '[') {
		clear(w, x+1,y+dy, dx,dy);
		w->g[y+dy][x+dx+1] = ']';
		w->g[y][x+1] = '.';
	}

	clear(w, x+dx,y+dy, dx,dy);
	w->g[y+dy][x+dx] = w->g[y][x];
	w->g[y][x] = '.';
}

static void
move(struct world *w, int dx, int dy)
{
	if (can_clear(w, w->px+dx, w->py+dy, dx,dy)) {
		clear(w, w->px+dx, w->py+dy, dx,dy);
		w->px += dx;
		w->py += dy;
	}
}

static int
score(struct world *w)
{
	int acc=0, x,y;

	for (y=0; y<GH && w->g[y][0]; y++)
	for (x=0; x<GW && w->g[y][x]; x++)
		if (w->g[y][x] == 'O' || w->g[y][x] == '[')
			acc += 100*y + x;

	return acc;
}

int
main(int argc, char **argv)
{
	static struct world w1,w2;
	int x,y, c;
	char *p;

	if (argc > 1)
		DISCARD(freopen(argv[1], "r", stdin));

	for (y=0; fgets(w1.g[y], GW, stdin); y++) {
		if (!w1.g[y][0] || w1.g[y][0]=='\n')
			break;

		assert(y+1 < GH);
		assert(strlen(w1.g[y])*2+1 < GW);

		for (x=0; w1.g[y][x]; x++)
			if (w1.g[y][x] == 'O') {
				w2.g[y][x*2]   = '[';
				w2.g[y][x*2+1] = ']';
			} else {
				w2.g[y][x*2]   = w1.g[y][x];
				w2.g[y][x*2+1] = w1.g[y][x];
			}

		if ((p = strchr(w1.g[y], '@'))) {
			w1.py = y; w1.px = p-w1.g[y];
			w2.py = y; w2.px = w1.px*2;

			w1.g[w1.py][w1.px]   = '.';
			w2.g[w2.py][w2.px]   = '.';
			w2.g[w2.py][w2.px+1] = '.';
		}
	}

	while ((c = getchar()) != EOF)
		switch (c) {
		case '^': move(&w1, 0,-1); move(&w2, 0,-1); break;
		case 'v': move(&w1, 0, 1); move(&w2, 0, 1); break;
		case '<': move(&w1,-1, 0); move(&w2,-1, 0); break;
		case '>': move(&w1, 1, 0); move(&w2, 1, 0); break;
		}

	printf("15: %d %d\n", score(&w1), score(&w2));
	return 0;
}