2024-15 in haskell

1 files changed, 164 insertions, 0 deletions

diff --git a/2024/15-Warehouse_Woes/second.hs b/2024/15-Warehouse_Woes/second.hs
new file mode 100644
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+++ b/2024/15-Warehouse_Woes/second.hs
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+-- requires cabal install --lib megaparsec parser-combinators heap vector
+module Main (main) where
+
+import           Control.Monad        (void, when)
+import           Data.Functor
+import qualified Data.List            as L
+import qualified Data.Vector          as V
+import           Data.Void            (Void)
+import           Text.Megaparsec
+import           Text.Megaparsec.Char
+
+exampleExpectedOutput = 9021
+
+data Tile = Wall | Box | Lbox | Rbox | Floor | Robot deriving (Eq, Show)
+type Line = V.Vector Tile
+type Warehouse = V.Vector Line
+data Op = N | S | E | W deriving (Eq, Show)
+data Input = Input Warehouse [Op] deriving Show
+
+type Parser = Parsec Void String
+
+parseTile :: Parser Tile
+parseTile = char '#' $> Wall
+        <|> char 'O' $> Box
+        <|> char '.' $> Floor
+        <|> char '@' $> Robot
+
+parseLine :: Parser Line
+parseLine = do
+  line <- some parseTile <* eol
+  return $ V.generate (length line) (line !!)
+
+parseOp :: Parser Op
+parseOp = char '^' $> N
+      <|> char 'v' $> S
+      <|> char '>' $> E
+      <|> char '<' $> W
+
+parseInput' :: Parser Input
+parseInput' = do
+  line <- some parseLine <* eol
+  ops <- some (parseOp <* optional eol) <* eof
+  return $ Input (V.generate (length line) (line !!)) ops
+
+parseInput :: String -> IO Input
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseInput' filename input of
+    Left bundle  -> error $ errorBundlePretty bundle
+    Right input' -> return input'
+
+type Coord = (Int, Int)
+
+next :: Coord -> Op -> Coord
+next (x, y) N = (x, y-1)
+next (x, y) S = (x, y+1)
+next (x, y) E = (x+1, y)
+next (x, y) W = (x-1, y)
+
+showWarehouse :: Warehouse -> String
+showWarehouse w = V.foldl' showOne [] w
+showOne acc line = acc ++ (V.foldl' showTile [] line) ++ "\n"
+showTile acc Wall  = acc ++ "#"
+showTile acc Lbox  = acc ++ "["
+showTile acc Rbox  = acc ++ "]"
+showTile acc Floor = acc ++ "."
+showTile acc Robot = acc ++ "@"
+showTile acc Box   = acc ++ "O"
+
+compute :: Input -> Int
+compute (Input warehouse ops) = V.ifoldl' scoreBoxes 0 warehouse''
+  where
+    scoreBoxes :: Int -> Int -> Line -> Int
+    scoreBoxes acc y line = V.ifoldl' (scoreBox y) acc line
+    scoreBox :: Int -> Int -> Int -> Tile -> Int
+    scoreBox y acc x Lbox = acc + 100 * y + x
+    scoreBox _ acc _ _    = acc
+    warehouse'' = fst $ L.foldl' step (warehouse', start) ops
+    step :: (Warehouse, Coord) -> Op -> (Warehouse, Coord)
+    step a@(w, r@(x, y)) op | t == Wall = a
+                            | t == Lbox = case push w r' op of
+                                Just w' -> (w', r')
+                                Nothing -> a
+                            | (op == N || op == S) && t == Rbox = case push w (x'-1, y') op of -- we want to always push boxes from their left side to reduce push cases
+                                Just w' ->(w', r')
+                                Nothing -> a
+                            | t == Rbox = case push w (x', y') op of
+                                Just w' -> (w', r')
+                                Nothing -> a
+                            | otherwise = (w, (x', y'))
+      where
+        r'@(x', y') = next r op
+        t = w V.! y' V.! x'
+    push :: Warehouse -> Coord -> Op -> Maybe Warehouse
+    push w r@(x, y) op | t == Wall = Nothing
+                       | (op == N || op == S) && tr == Wall = Nothing
+                       | (op == N || op == S) && t == Lbox = case push w (x, y') op of -- pushing a boxes that matches ours
+                           Just w' -> let l1 = w' V.! y
+                                          l1' = l1 V.// [(x, Floor), (x+1, Floor)]
+                                          l2 = w' V.! y'
+                                          l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
+                                      in Just (w' V.// [(y, l1'), (y', l2')])
+                           Nothing -> Nothing
+                       | (op == N || op == S) && t == Rbox = case push w (x-1, y') op of
+                           Just w' -> if tr == Lbox then case push w' (x+1, y') op of -- are we pushing two boxes?
+                                                           Just w'' -> let l1 = w'' V.! y
+                                                                           l1' = l1 V.// [(x, Floor), (x+1, Floor)]
+                                                                           l2 = w'' V.! y'
+                                                                           l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
+                                                                       in Just (w'' V.// [(y, l1'), (y', l2')])
+                                                           Nothing -> Nothing
+                                                    else let l1 = w' V.! y -- or just one on our left
+                                                             l1' = l1 V.// [(x, Floor), (x+1, Floor)]
+                                                             l2 = w' V.! y'
+                                                             l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
+                                                         in Just (w' V.// [(y, l1'), (y', l2')])
+                           Nothing -> Nothing
+                       | (op == N || op == S) && tr == Lbox = case push w (x+1, y') op of -- or just one on our right
+                           Just w' -> let l1 = w' V.! y
+                                          l1' = l1 V.// [(x, Floor), (x+1, Floor)]
+                                          l2 = w' V.! y'
+                                          l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
+                                      in Just (w' V.// [(y, l1'), (y', l2')])
+                           Nothing -> Nothing
+                       | (op == N || op == S) = let l1 = w V.! y -- free space
+                                                    l1' = l1 V.// [(x, Floor), (x+1, Floor)]
+                                                    l2 = w V.! y'
+                                                    l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
+                                                in Just (w V.// [(y, l1'), (y', l2')])
+                       | t == Lbox || t == Rbox = case push w (x', y) op of -- East-West movements are simpler
+                           Just w' -> let l = w' V.! y
+                                          l' = l V.// [(x, Floor), (x', to)]
+                                      in Just (w' V.// [(y, l')])
+                           Nothing -> Nothing
+                       | otherwise = let l = w V.! y -- free space
+                                         l' = l V.// [(x, Floor), (x', to)]
+                                     in Just (w V.// [(y, l')])
+      where
+        (x', y') = next r op
+        t = w V.! y' V.! x'
+        tr = w V.! y' V.! (x'+1)
+        to = w V.! y V.! x
+    start = V.ifoldl' findRobot (0, 0) warehouse'
+    findRobot :: (Int, Int) -> Int -> Line -> (Int, Int)
+    findRobot (0, _) y line = (V.ifoldl' findRobotInLine 0 line, y)
+    findRobot a _ _         = a
+    findRobotInLine :: Int -> Int -> Tile -> Int
+    findRobotInLine 0 x Robot = x
+    findRobotInLine a _ _     = a
+    wideWidth = 2 * V.length (warehouse V.! 0)
+    warehouse' = V.map widen warehouse
+    widen line = V.ifoldl' widenOne (V.replicate wideWidth Floor) line
+    widenOne acc x Wall  = acc V.// [(2*x, Wall), (2*x+1, Wall)]
+    widenOne acc x Box   = acc V.// [(2*x, Lbox), (2*x+1, Rbox)]
+    widenOne acc x Robot = acc V.// [(2*x, Robot)]
+    widenOne acc _ _     = acc
+
+main :: IO ()
+main = do
+  example <- parseInput "example2"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input