Day 10

day10/Commons.hs

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+module Commons where
+
+import GHC.IO.Handle (isEOF)
+import Data.Array (Array, listArray, (!), indices)
+
+
+data Direction = North | East | West | South deriving (Eq, Show)
+data Tile = Ground | Start | Pipe (Direction, Direction) deriving (Eq, Show)
+type Grid = Array (Int, Int) Tile
+
+
+parseLine :: String -> [Tile]
+parseLine [] = []
+parseLine ('.': t) = Ground: parseLine t
+parseLine ('S': t) = Start: parseLine t
+parseLine ('|': t) = Pipe (North, South): parseLine t
+parseLine ('-': t) = Pipe (East, West): parseLine t
+parseLine ('L': t) = Pipe (North, East): parseLine t
+parseLine ('J': t) = Pipe (North, West): parseLine t
+parseLine ('7': t) = Pipe (South, West): parseLine t
+parseLine ('F': t) = Pipe (South, East): parseLine t
+
+parseGrid :: [[Tile]] -> IO Grid
+parseGrid otherTiles = do done <- isEOF
+                          if done
+                             then return $ listArray ((1, 1), (length otherTiles, length (otherTiles !! 1)))
+                                         $ concat otherTiles
+                             else do line <- getLine
+                                     let tiles = parseLine line
+                                     parseGrid (otherTiles ++ [tiles])
+
+parse :: IO Grid
+parse = parseGrid []
+
+
+findStart :: [(Int, Int)] -> Grid -> (Int, Int)
+findStart (h: t) grid | grid ! h == Start = h
+                      | otherwise         = findStart t grid
+
+getStartCoordinates :: Grid -> (Int, Int)
+getStartCoordinates grid = findStart (indices grid) grid
+
+getStartDirection :: (Int, Int) -> Grid -> (Direction, (Int, Int))
+getStartDirection (y, x) grid | grid ! (y + 1, x) == Pipe (North, South) = (South, (y + 1, x))
+                              | grid ! (y + 1, x) == Pipe (North, East) = (South, (y + 1, x))
+                              | grid ! (y + 1, x) == Pipe (North, West) = (South, (y + 1, x))
+                              | grid ! (y, x + 1) == Pipe (East, West) = (East, (y, x + 1))
+                              | grid ! (y, x + 1) == Pipe (North, West) = (East, (y, x + 1))
+                              | grid ! (y, x + 1) == Pipe (South, West) = (East, (y, x + 1))