Day 15: Warehouse Woes
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Uiua
Put this one off for a bit and I’ll put off part two for even longer because I don’t want to deal with any pyramid-shapes of boxes at the moment.
The code for part one feels too long but it works and runs <2s so I’m happy with it for now ^^Run with example input here
Code
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 PartTwoHaskell
This was a fun one! I’m quite pleased with
moveInto, which could be easily extended to support arbitrary box shapes.Solution
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]Nim
Very fiddly solution with lots of debugging required.
Code
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
TypeScript
Not very optimized code today. Basically just a recursive function
Code
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!"); }Dart
canMovedoes a recursive search and returns all locations that need moving, or none if there’s an obstacle anywhere downstream. For part2, that involves checking if there’s half of a box in front of us, and if so ensuring that we also check the other half of that box. I don’t bother tracking whether we’re double-checking as it runs fast enough as is.import 'dart:math'; import 'package:collection/collection.dart'; import 'package:more/more.dart'; var d4 = <Point<num>>[Point(1, 0), Point(-1, 0), Point(0, 1), Point(0, -1)]; var m4 = '><v^'; solve(List<String> lines, {wide = false}) { if (wide) { lines = lines .map((e) => e .replaceAll('#', '##') .replaceAll('.', '..') .replaceAll('O', '[]') .replaceAll('@', '@.')) .toList(); } var room = { for (var r in lines.takeWhile((e) => e.isNotEmpty).indexed()) for (var c in r.value.split('').indexed().where((c) => (c.value != '.'))) Point<num>(c.index, r.index): c.value }; var bot = room.entries.firstWhere((e) => e.value == '@').key; var moves = lines.skipTo('').join('').split(''); for (var d in moves.map((m) => d4[m4.indexOf(m)])) { if (didMove(d, bot, room)) bot += d; } return room.entries .where((e) => e.value == '[' || e.value == 'O') .map((e) => e.key.x + 100 * e.key.y) .sum; } bool didMove(Point m, Point here, Map<Point, String> room) { var moves = canMove(m, here, room).toSet(); if (moves.isNotEmpty) { var vals = moves.map((e) => room.remove(e)!).toList(); for (var ms in moves.indexed()) { room[ms.value + m] = vals[ms.index]; } return true; } return false; } List<Point> canMove(Point m, Point here, Map<Point, String> room) { if (room[here + m] == '#') return []; if (!room.containsKey(here + m)) return [here]; var cm1 = canMove(m, here + m, room); if (m.x != 0) return (cm1.isEmpty) ? [] : cm1 + [here]; List<Point> cm2 = [here]; if (room[here + m] == '[') cm2 = canMove(m, here + m + Point(1, 0), room); if (room[here + m] == ']') cm2 = canMove(m, here + m - Point(1, 0), room); return cm1.isEmpty || cm2.isEmpty ? [] : cm1 + cm2 + [here]; }Rust
Part 2 was a bit tricky. Moving into a box horizontally works mostly the same as for part 1, for the vertical case I used two recursive functions. The first recurses from the left and right side for each box just to find out if the entire tree can be moved. The second function actually does the moving in a similar recursive structure, but now with the knowledge that all subtrees can actually be moved.
Lots of moving parts, but at least it could very nicely be debugged by printing out the map from the two minimal examples after each round.
Solution
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!();Also on github
Haskell
Runs in 12 ms. I was very happy with my code for part 1, but will sadly have to rewrite it completely for part 2.
Code
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']J
Nothing much to say about today’s. I think I wrote basically the same code you’d write in Python, just with fewer characters, more of which are punctuation. I did learn a little bit more about how to use J’s step debugger, and that
/is specifically a right fold, so you can use it on a dyad with arguments of different types as long as the list argument is the left one.data_file_name =: '15.data' lines =: cutopen fread data_file_name NB. instructions start with the first line not containing a # character start_of_moves =: 0 i.~ '#' e."1 > lines grid =: ,. > start_of_moves {. lines start_row =: 1 i.~ '@' e."1 grid start_col =: '@' i.~ start_row { grid pos =: start_row, start_col grid =: '.' ( start_of_moves }. lines translate_move =: monad define"0 if. y = '>' do. 0 1 elseif. y = '^' do. _1 0 elseif. y = '<' do. 0 _1 elseif. y = 'v' do. 1 0 else. 0 0 end. ) moves =: translate_move move_instructions NB. pos step move updates grid as needed and returns the new position step =: dyad define"1 1 new_pos =. x + y if. '#' = (< new_pos) { grid do. x NB. obstructed by wall elseif. '.' = (< new_pos) { grid do. new_pos NB. free to move else. NB. it's 'O', need to push a stack p =. new_pos NB. pointer to box at end of stack while. 'O' = (< p) { grid do. p =. p + y end. if. '#' = (< p) { grid do. x NB. stack is blocked else. NB. move stack grid =: 'O.' (< p ,: new_pos)} grid new_pos end. end. ) score =: dyad define"0 2 +/ ; ((<"0) 100 * i.#y) +&.> (< @: I. @: = & x)"1 y ) final_pos =: step~/ |. pos , moves NB. / is a right fold result1 =: 'O' score grid translate_cell =: monad define"0 if. y = '#' do. '##' elseif. y = '.' do. '..' elseif. y = 'O' do. '[]' else. '@.' end. ) grid2 =: (,/ @: translate_cell)"1 ,. > start_of_moves {. lines start_row2 =: 1 i.~ '@' e."1 grid2 start_col2 =: '@' i.~ start_row { grid2 pos =: start_row2, start_col2 grid2 =: '.' (< pos)} grid2 NB. erase the @ NB. (grid; box_pos) try_push dir attempts to push the box at box_pos one NB. cell in direction dir. box_pos can be either the left or right cell of NB. the box. it returns (grid; success) where grid is the maybe-changed grid NB. and success is whether the box moved. if any box that would be pushed NB. cannot move, this box cannot move either and the grid does not change. try_push =: dyad define"1 1 'grid pos' =. x if. ']' = (< pos) { grid do. pos =. pos + 0 _1 end. NB. make pos left cell source_cells =. pos ,: pos + 0 1 if. 0 = {: y do. NB. moving up or down target_cells =. (pos + y) ,: (pos + y + 0 1) NB. cells we move into elseif. y -: 0 _1 do. target_cells =. 1 2 $ pos + y NB. moving left else. target_cells =. 1 2 $ pos + y + 0 1 end. NB. moving right NB. Have to check target cells one at a time because pushing a box up or NB. down may vacate the other target cell, or it may not trial_grid =. grid for_tc. target_cells do. NB. if a target cell is blocked by wall, fail if. '#' = (< tc) { trial_grid do. grid; 0 return. elseif. '[]' e.~ (< tc) { trial_grid do. 'trial_grid success' =. (trial_grid; tc) try_push y if. -. success do. grid; 0 return. end. end. end. NB. at this point either target_cells are clear or we have returned failure, NB. so push the box grid =. '[]' (<"1 source_cells +"1 y)} '.' (<"1 source_cells)} trial_grid grid; 1 ) NB. (grid; pos) step2 move executes the move and returns new (grid; pos) step2 =: dyad define"1 1 'grid pos' =. x new_pos =. pos + y if. '#' = (< new_pos) { grid do. grid; pos NB. obstructed by wall elseif. '.' = (< new_pos) { grid do. grid; new_pos NB. free to move else. NB. need to push a box 'new_grid success' =. (grid; new_pos) try_push y if. success do. new_grid; new_pos else. grid; pos end. end. ) 'final_grid final_pos' =: > (step2~ &.>)/ (<"1 |. moves) , <(grid2; pos) result2 =: '[' score final_gridRust
The work is all in the “push” method. The robot pushes one square, which may chain to additional squares. HashSet probably isn’t the optimal data structure, but it’s good enough.
Large codeblock
/// 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)); }C#
beautiful
public class Day15 : Solver { private char[][] map; private int width, height; private string movements; public void Presolve(string input) { var blocks = input.Trim().Split("\n\n").ToList(); map = blocks[0].Split("\n").Select(line => line.ToArray()).ToArray(); width = map[0].Length; height = map.Length; movements = blocks[1]; } public string SolveFirst() { var data = map.Select(row => row.ToArray()).ToArray(); int robot_x = -1, robot_y = -1; for (int i = 0; i < width; i++) { for (int j = 0; j < height; j++) { if (data[j][i] == '@') { robot_x = i; robot_y = j; data[j][i] = '.'; break; } } } foreach (var m in movements) { var (dx, dy) = m switch { '^' => (0, -1), '>' => (1, 0), 'v' => (0, 1), '<' => (-1, 0), _ => (0, 0) }; if ((dx, dy) == (0, 0)) continue; var (x, y) = (robot_x + dx, robot_y + dy); if (data[y][x] == '#') continue; if (data[y][x] == '.') { (robot_x, robot_y) = (x, y); continue; } var (end_of_block_x, end_of_block_y) = (x + dx, y + dy); while (data[end_of_block_y][end_of_block_x] == 'O') { (end_of_block_x, end_of_block_y) = (end_of_block_x + dx, end_of_block_y + dy); } if (data[end_of_block_y][end_of_block_x] == '.') { data[end_of_block_y][end_of_block_x] = 'O'; data[y][x] = '.'; (robot_x, robot_y) = (x, y); } } long answer = 0; for (int i = 0; i < width; i++) { for (int j = 0; j < height; j++) { if (data[j][i] == 'O') { answer += i + 100 * j; } } } return answer.ToString(); } public string SolveSecond() { var expanded_data = map.Select(row => row.SelectMany<char, char>(ch => ch switch { '#' => ['#', '#'], 'O' => ['[', ']'], '.' => ['.', '.'], '@' => ['@', '.'] }).ToArray()).ToArray(); int robot_x = -1, robot_y = -1; for (int i = 0; i < width * 2; i++) { for (int j = 0; j < height; j++) { if (expanded_data[j][i] == '@') { robot_x = i; robot_y = j; expanded_data[j][i] = '.'; break; } } } if (robot_x < 0) throw new InvalidDataException(); foreach (var m in movements) { var (dx, dy) = m switch { '^' => (0, -1), '>' => (1, 0), 'v' => (0, 1), '<' => (-1, 0), _ => (0, 0) }; if ((dx, dy) == (0, 0)) continue; var (x, y) = (robot_x + dx, robot_y + dy); if (expanded_data[y][x] == '#') continue; if (expanded_data[y][x] == '.') { (robot_x, robot_y) = (x, y); continue; } if (dy == 0) { var (end_of_block_x, end_of_block_y) = (x + dx * 2, y); while (expanded_data[end_of_block_y][end_of_block_x] == '[' || expanded_data[end_of_block_y][end_of_block_x] == ']') { (end_of_block_x, end_of_block_y) = (end_of_block_x + dx, end_of_block_y); } if (expanded_data[end_of_block_y][end_of_block_x] == '.') { var (fill_start, fill_end) = dx > 0 ? (x + 1, end_of_block_x) : (end_of_block_x, x); for (int fill_x = fill_start; fill_x < fill_end; fill_x += 2) { expanded_data[y][fill_x] = '['; expanded_data[y][fill_x + 1] = ']'; } expanded_data[y][x] = '.'; (robot_x, robot_y) = (x, y); } continue; } List<(int, int)> boxes_to_move = [(x, y)]; if (expanded_data[y][x] == ']') { boxes_to_move.Add((x - 1, y)); } else { boxes_to_move.Add((x + 1, y)); } List<(int, int)> boxes_move_ordered = []; bool impossible = false; while (boxes_to_move.Count > 0) { HashSet<(int, int)> next_boxes = []; foreach (var (box_x, box_y) in boxes_to_move) { boxes_move_ordered.Add((box_x, box_y)); if (expanded_data[box_y + dy][box_x] == '.') continue; if (expanded_data[box_y + dy][box_x] == '#') { impossible = true; break; } next_boxes.Add((box_x, box_y + dy)); if (expanded_data[box_y + dy][box_x] == ']') { next_boxes.Add((box_x - 1, box_y + dy)); } else { next_boxes.Add((box_x + 1, box_y + dy)); } } if (impossible) break; boxes_to_move = [..next_boxes]; } if (impossible) continue; boxes_move_ordered.Reverse(); foreach (var (box_x, box_y) in boxes_move_ordered) { expanded_data[box_y + dy][box_x] = expanded_data[box_y][box_x]; expanded_data[box_y][box_x] = '.'; } (robot_x, robot_y) = (x, y); } long answer = 0; for (int i = 0; i < width * 2; i++) { for (int j = 0; j < height; j++) { if (expanded_data[j][i] == '[') { answer += i + 100 * j; } } } return answer.ToString(); } }C
3h+ train ride back home from weekend trip but a little tired and not feeling it much. Finished part 1, saw that part 2 was fiddly programming, left it there.
Finally hacked together something before bed. The part 2 twist required rewriting the push function to be recursive but also a little care and debugging to get that right. Cleaned it up over lunch, happy enough with the solution now!
Code
#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; }
