45 lines
1.3 KiB
Haskell
45 lines
1.3 KiB
Haskell
module Day3_1 where
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import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
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import Data.List ( maximumBy, minimumBy, group, sort )
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import Data.Function (on)
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import Data.Char (digitToInt)
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column :: [String] -> Int -> String
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column str i = map (!! i) str
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mostCommon :: String -> Char
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mostCommon str = head . maximumBy (compare `on` length) . group $ sort str
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leastCommon :: String -> Char
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leastCommon str = head . minimumBy (compare `on` length) . group $ sort str
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-- in: input strings, sorting method, current digit
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-- out: filtered strings
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filterColumns :: [String] -> (String -> Char) -> Int -> [String]
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filterColumns str sort i = filter (\a -> (a !! i) == commonChar) str
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where
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commonChar = sort $ column str i
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-- in: input strings, sorting method, current digit
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-- out: final rating
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rating :: [String] -> (String -> Char) -> Int -> String
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rating [str] _ _ = str
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rating str sort i = rating (filterColumns str sort i) sort (i+1)
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binaryToDecimal :: Int -> Int
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binaryToDecimal = foldl1 ((+) . (2 *)) . map digitToInt . show
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main :: IO ()
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main = do
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input <- openFile "inputs/3.txt" ReadMode
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contents <- hGetContents input
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let oxygen = rating (lines contents) mostCommon 0
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let co2 = rating (lines contents) leastCommon 0
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let rating = product (binaryToDecimal . read <$> [oxygen, co2] :: [Int])
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print rating
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hClose input |