2022-22 part 2 in haskell

2022/22-Monkey-Map/second.hs

@@ -0,0 +1,143 @@
+-- requires cabal install --lib megaparsec parser-combinators vector
+module Main (main) where
+import Control.Monad (void, when)
+import Data.Functor
+import Data.List qualified as L
+import Data.Maybe
+import Data.Vector qualified as V
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import System.Exit (die)
+
+exampleExpectedOutput = 5031
+
+type Line = V.Vector Char
+type Map = V.Vector Line
+data Instruction = Move Int | L | R deriving Show
+data Input = Input Map [Instruction] deriving Show
+
+type Parser = Parsec Void String
+
+parseMapLine :: Parser Line
+parseMapLine = do
+  line <- some (char '.' <|> char ' ' <|> char '#') <* char '\n'
+  return $ V.generate (length line) (line !!)
+
+parseMap :: Parser Map
+parseMap = do
+  lines <- some parseMapLine <* char '\n'
+  return $ V.generate (length lines) (lines !!)
+
+parseInstruction :: Parser Instruction
+parseInstruction = (Move . read <$> some digitChar)
+               <|> (char 'L' $> L)
+               <|> (char 'R' $> R)
+
+parseInput' :: Parser Input
+parseInput' = do
+  m <- parseMap
+  i <- some parseInstruction
+  void $ optional (char '\n') <* eof
+  return $ Input m i
+
+parseInput :: String -> IO Input
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseInput' filename input of
+    Left bundle -> die $ errorBundlePretty bundle
+    Right input' -> return input'
+
+data Heading = N | S | E | W deriving (Eq, Show)
+data Cursor = Cursor Int Int Heading
+
+isOut :: Map -> Int -> Int -> Bool
+isOut m x y = isNothing line || isNothing tile || tile == Just ' '
+  where
+    line = m V.!? y
+    tile = fromJust line V.!? x
+
+stepOutside :: Map -> Int -> Int -> Int -> Heading -> Int -> Cursor
+stepOutside m s x y h i | (t, h) == (a, N) = proceed fw (fn + rx) E
+                        | (t, h) == (a, W) = proceed dw (ds - ry) E
+                        | (t, h) == (b, N) = proceed (fw + rx) fs N
+                        | (t, h) == (b, E) = proceed ee (es - ry) W
+                        | (t, h) == (b, S) = proceed ce (cn + rx) W
+                        | (t, h) == (c, W) = proceed (dw + ry) dn S
+                        | (t, h) == (c, E) = proceed (bw + ry) bs N
+                        | (t, h) == (d, N) = proceed cw (cn + rx) E
+                        | (t, h) == (d, W) = proceed aw (as - ry) E
+                        | (t, h) == (e, E) = proceed be (bs - ry) W
+                        | (t, h) == (e, S) = proceed fe (fn + rx) W
+                        | (t, h) == (f, W) = proceed (aw + ry) an S
+                        | (t, h) == (f, S) = proceed (bw + rx) bn S
+                        | (t, h) == (f, E) = proceed (ew + ry) es N
+  where
+    (tx, rx) = x `divMod` s
+    (ty, ry) = y `divMod` s
+    t = (tx, ty)
+    proceed :: Int -> Int -> Heading -> Cursor
+    proceed x' y' h' = case m V.! y' V.! x' of
+      '.' -> step m s (Cursor x' y' h') (Move $ i - 1)
+      '#' -> Cursor x y h
+    a = (ax, ay)
+    b = (bx, by)
+    c = (cx, cy)
+    d = (dx, dy)
+    e = (ex, ey)
+    f = (fx, fy)
+    (ax, ay) = (1, 0)
+    (bx, by) = (2, 0)
+    (cx, cy) = (1, 1)
+    (dx, dy) = (0, 2)
+    (ex, ey) = (1, 2)
+    (fx, fy) = (0, 3)
+    (an, as, aw, ae) = (ay * s, (ay+1)*s-1, ax *s, (ax+1)*s-1)
+    (bn, bs, bw, be) = (by * s, (by+1)*s-1, bx *s, (bx+1)*s-1)
+    (cn, cs, cw, ce) = (cy * s, (cy+1)*s-1, cx *s, (cx+1)*s-1)
+    (dn, ds, dw, de) = (dy * s, (dy+1)*s-1, dx *s, (dx+1)*s-1)
+    (en, es, ew, ee) = (ey * s, (ey+1)*s-1, ex *s, (ex+1)*s-1)
+    (fn, fs, fw, fe) = (fy * s, (fy+1)*s-1, fx *s, (fx+1)*s-1)
+
+step :: Map -> Int -> Cursor -> Instruction -> Cursor
+step _ _ (Cursor x y N) L = Cursor x y W
+step _ _ (Cursor x y S) L = Cursor x y E
+step _ _ (Cursor x y E) L = Cursor x y N
+step _ _ (Cursor x y W) L = Cursor x y S
+step _ _ (Cursor x y N) R = Cursor x y E
+step _ _ (Cursor x y S) R = Cursor x y W
+step _ _ (Cursor x y E) R = Cursor x y S
+step _ _ (Cursor x y W) R = Cursor x y N
+step m _ c (Move 0) = c
+step m s (Cursor x y h) (Move i) | isOut m x' y' = stepOutside m s x y h i
+                                 | tile == '.' = step m s (Cursor x' y' h) (Move $ i - 1)
+                                 | tile == '#' = Cursor x y h
+  where
+    (x', y') = case h of
+      N -> (x, y-1)
+      S -> (x, y+1)
+      E -> (x+1, y)
+      W -> (x-1, y)
+    tile = m V.! y' V.! x'
+
+compute :: Input -> Int
+compute (Input m i) = 1000 * (y+1) + 4 * (x+1) + hv
+  where
+    xmin = length (V.filter (== ' ') (m V.! 0))
+    startingCursor = Cursor xmin 0 E
+    s = length (m V.! 0) `div` 3
+    Cursor x y h = L.foldl' (step m s) startingCursor i
+    hv = case h of
+      E -> 0
+      S -> 1
+      W -> 2
+      N -> 3
+
+main :: IO ()
+main = do
+  -- not doing the example, this solution is dependent on the shape of the input cube and sadly the example does not match it
+  -- example <- parseInput "example"
+  -- let exampleOutput = compute example
+  -- when  (exampleOutput /= exampleExpectedOutput)  (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input