35 lines
1.4 KiB
Haskell
35 lines
1.4 KiB
Haskell
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import Data.List (elemIndex)
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import Data.Matrix (Matrix, fromLists, (!))
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type Grid = Matrix Char
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data Direction = North | South | West | East | Stop deriving Eq
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data State = State (Int, Int) Direction [Char] Int
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nextState :: String -> Grid -> State -> State
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nextState letters grid (State (r, c) dir seen count) =
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let (nextR, nextC) = case dir of
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North -> (r - 1, c)
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South -> (r + 1, c)
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West -> (r, c - 1)
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East -> (r, c + 1)
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nextChar = grid ! (nextR, nextC)
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nextDir = case nextChar of
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'+' -> if dir `elem` [North, South]
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then if grid ! (nextR, nextC - 1) == '-' then West else East
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else if grid ! (nextR - 1, nextC) == '|' then North else South
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' ' -> Stop
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_ -> dir
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nextSeen = if nextChar `elem` letters then nextChar : seen else seen
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in State (nextR, nextC) nextDir nextSeen (count + 1)
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traverseGrid :: String -> Grid -> State -> (String, Int)
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traverseGrid _ _ (State _ Stop seen count) = (reverse seen, count)
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traverseGrid letters grid state = traverseGrid letters grid $ nextState letters grid state
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main :: IO ()
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main = do
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input <- readFile "19.txt"
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let rows = lines input
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Just start = (+1) <$> (elemIndex '|' $ head rows)
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letters = filter (not . (`elem` " +|-\n")) input
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print $ traverseGrid letters (fromLists rows) (State (1, start) South [] 0)
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