src/advent13/advent13.hs

   1 {-# LANGUAGE NegativeLiterals #-}
   2 {-# LANGUAGE FlexibleContexts #-}
   3 {-# LANGUAGE OverloadedStrings #-}
   4
   5 import Data.Text (Text)
   6 import qualified Data.Text as T
   7 import qualified Data.Text.IO as TIO
   8
   9 import Text.Megaparsec
  10 import qualified Text.Megaparsec.Lexer as L
  11 import Text.Megaparsec.Text (Parser)
  12
  13 import qualified Control.Applicative as CA
  14
  15 type ScannerDef = (Integer, Integer)
  16 type Scanner = Integer -> Integer
  17
  18
  19 main :: IO ()
  20 main = do
  21         text <- TIO.readFile "data/advent13.txt"
  22         let scannerDefs = successfulParse text
  23         print $ part1 scannerDefs
  24         print $ part2 scannerDefs
  25
  26
  27 part1 :: [ScannerDef] -> Integer
  28 part1 = sum . map (uncurry (*)) . filter (\(d, r) -> scanner d r 0 == 0)
  29
  30
  31 part2 :: [ScannerDef] -> Integer
  32 part2 scannerDefs = head $ filter (canPass scanners) [0..]
  33     where scanners = scanify scannerDefs
  34
  35
  36 scanify :: [ScannerDef] -> [Scanner]
  37 scanify = map (uncurry scanner)
  38
  39 canPass :: [Scanner] -> Integer -> Bool
  40 canPass scannersF t = all (\s -> s t /= 0) scannersF
  41
  42
  43 scanner :: Integer -> Integer -> Integer -> Integer
  44 scanner depth range t =
  45     let t' = (t + depth) `mod` ((range - 1) * 2)
  46     in if t' < range
  47        then t'
  48        else range - t' - 1 -- t' + (t' - range + 1) * -2
  49
  50
  51 sc :: Parser ()
  52 sc = L.space (skipSome spaceChar) CA.empty CA.empty
  53
  54 lexeme  = L.lexeme sc
  55 integer = lexeme L.integer
  56 symb = L.symbol sc
  57
  58 scannersP = many scannerP
  59
  60 scannerP = (,) <$> integer <*> (symb ":" *> integer)
  61
  62 successfulParse :: Text -> [ScannerDef]
  63 successfulParse input =
  64         case parse scannersP "input" input of
  65                 Left  err   -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
  66                 Right scanners -> scanners