54 lines
1.3 KiB
Haskell
54 lines
1.3 KiB
Haskell
{-# LANGUAGE OverloadedStrings #-}
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module Day01 (parse, solveA, solveB) where
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import qualified Data.Text as T
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import Data.Text (Text)
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import Data.Char (isDigit)
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import Data.Maybe (mapMaybe, listToMaybe)
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parse :: Text -> [Text]
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parse = T.lines
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merge :: [Int] -> Int
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merge xs = 10 * head xs + last xs
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solveA :: [Text] -> Int
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solveA = sum . map (merge . convert)
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where
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convert :: Text -> [Int]
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convert = map (read . pure) . T.unpack . T.filter isDigit
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replaces :: [(Text, Int)]
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replaces =
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[ ("one", 1)
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, ("two", 2)
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, ("three", 3)
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, ("four", 4)
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, ("five", 5)
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, ("six", 6)
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, ("seven", 7)
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, ("eight", 8)
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, ("nine", 9)
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]
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solveB :: [Text] -> Int
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solveB = sum . map (merge . convert)
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where
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-- If `text` starts with `prefix` return `Just n`, otherwise return `Nothing`
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tryReplace :: Text -> (Text, Int) -> Maybe Int
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tryReplace text (prefix, n)
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| prefix `T.isPrefixOf` text = Just n
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| otherwise = Nothing
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-- If `firstChar` is a digit return it, otherwise try replace the prefix
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parsePrefix :: Text -> Maybe Int
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parsePrefix text
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| isDigit firstChar = Just . read . pure $ firstChar
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| otherwise = listToMaybe $ mapMaybe (tryReplace text) replaces
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where
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firstChar = T.head text
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convert :: Text -> [Int]
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convert = mapMaybe parsePrefix . filter (not . T.null) . T.tails
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