advent01/src/advent01.hs

   1 {-# LANGUAGE NegativeLiterals #-}
   2 {-# LANGUAGE OverloadedStrings #-}
   3
   4 import Data.Text (Text)
   5 import qualified Data.Text.IO as TIO
   6
   7 import Data.Void (Void)
   8
   9 import Text.Megaparsec
  10 import Text.Megaparsec.Char
  11 import qualified Text.Megaparsec.Char.Lexer as L
  12 import qualified Control.Applicative as CA
  13
  14 import Data.IntSet (IntSet)
  15 import qualified Data.IntSet as S
  16
  17 main :: IO ()
  18 main = do
  19         text <- TIO.readFile "data/advent01.txt"
  20         let changes = successfulParse text
  21         print $ part1 changes
  22         print $ part2 changes
  23
  24
  25 part1 :: [Int] -> Int
  26 part1 = sum
  27
  28 part2 :: [Int] -> Int
  29 part2 = snd . head . dropWhile unRepeated . scanl merge (S.empty, 0) . cycle
  30
  31 merge :: (IntSet, Int) -> Int -> (IntSet, Int)
  32 merge (frequencies, frequency) change = (S.insert frequency frequencies, frequency + change)
  33
  34 unRepeated :: (IntSet, Int) -> Bool
  35 unRepeated (frequencies, frequency) = frequency `S.notMember` frequencies
  36
  37 -- Parse the input file
  38 type Parser = Parsec Void Text
  39
  40 sc :: Parser ()
  41 sc = L.space (skipSome spaceChar) CA.empty CA.empty
  42 -- sc = L.space (skipSome (char ' ')) CA.empty CA.empty
  43
  44
  45 lexeme  = L.lexeme sc
  46 integer = lexeme L.decimal
  47 signedInteger = L.signed sc integer
  48
  49 changesP = many signedInteger
  50
  51 successfulParse :: Text -> [Int]
  52 successfulParse input =
  53         case parse changesP "input" input of
  54                 Left  _err -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
  55                 Right changes -> changes