46 lines
1.2 KiB
Haskell
46 lines
1.2 KiB
Haskell
import Data.List
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import Data.Maybe
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type Path = ([String], [(Int, Int)])
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main :: IO ()
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main = do
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input <- lines <$> readFile "input"
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let s = findLetter 'S' input
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let e = findLetter 'E' input
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print $ step e (input, []) [s]
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findLetter :: Char -> [String] -> (Int, Int)
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findLetter c = f <*> fromJust . findIndex (/= Nothing) <$> map (elemIndex c)
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where
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f x y = (head $ catMaybes x, y)
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step :: (Int,Int)->Path -> [(Int, Int)] -> Int
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step c (field, visited) active
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| c `elem` active = 0
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| otherwise = 1 + step c (field, active ++ visited) next
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where next = nub $ sort $ concatMap (nextSteps (field, visited)) active
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nextSteps :: Path -> (Int, Int) -> [(Int, Int)]
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nextSteps (field, visited) (x, y) =
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[ (x + x', y + y')
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| x' <- [-1 .. 1]
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, x' + x >= 0
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, x' + x < lenX
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, y' <- [-1 .. 1]
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, y' + y >= 0
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, y + y' < lenY
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, abs x' /= abs y'
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, let a = field !! (y + y') !! (x + x')
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in (a `elem` ['a' .. succ current] || (a == 'E' && current == 'z'))
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, (x + x', y + y') `notElem` visited
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]
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where
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lenX = length $ head field
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lenY = length field
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char = field !! y !! x
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current
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| char == 'S' = 'a'
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| char == 'E' = 'z'
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| otherwise = char
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