40 lines
1.6 KiB
Haskell
40 lines
1.6 KiB
Haskell
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import Data.List.Split
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import Data.List
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import Data.Maybe
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getRightMin :: [Integer] -> [Integer] -> Maybe Integer
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getRightMin prevRight currRight =
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case currRight of
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[] -> Nothing
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_ -> Just $ minimum $ zipWith (+) prevRight $ tail $ scanl (+) 0 currRight
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getLeftMin :: [Integer] -> [Integer] -> Maybe Integer
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getLeftMin prevLeft currLeft = getRightMin (reverse prevLeft) (reverse currLeft)
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type Acc = ([Integer], [Integer], [Integer], [Integer])
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type PrevCurr = (Integer, Integer)
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getMin :: Acc -> PrevCurr -> Integer
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getMin (prevLeft, currLeft, prevRight, currRight) (prev, curr) =
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curr + (minimum $ catMaybes [getLeftMin prevLeft currLeft, Just prev, getRightMin prevRight currRight])
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shift :: Acc -> PrevCurr -> Acc
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shift (prevLeft, currLeft, prevRight, currRight) (prev, curr) =
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(prevLeft ++ [prev], currLeft ++ [curr], tail prevRight, tail currRight)
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getNextLine :: [Integer] -> [Integer] -> [Integer]
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getNextLine prevLine currLine =
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let initPrevLeft = []
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initCurrLeft = []
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initPrevRight = tail prevLine
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initCurrRight = tail currLine
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next acc prevCurr = (shift acc prevCurr, getMin acc prevCurr)
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in snd $ mapAccumL next (initPrevLeft, initCurrLeft, initPrevRight, initCurrRight) $ zip prevLine currLine
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main :: IO ()
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main = do
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contents <- readFile "p081_matrix.txt"
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let fileLines = lines contents
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upDownMatrix = map (map read . (splitOn ",")) fileLines
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matrix = transpose upDownMatrix
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print $ minimum $ foldl getNextLine (head matrix) (tail matrix)
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