advent13/src/advent13.hs

   1 -- import Debug.Trace
   2
   3 import Data.Text (Text)
   4 -- import qualified Data.Text as T
   5 import qualified Data.Text.IO as TIO
   6
   7 import Data.Attoparsec.Text
   8 -- import Data.Attoparsec.Combinator
   9 import Control.Applicative
  10 import Data.Maybe
  11 import Data.List
  12 import Math.NumberTheory.Moduli.Chinese
  13
  14
  15
  16 main :: IO ()
  17 main =
  18   do  text <- TIO.readFile "data/advent13.txt"
  19       let (timestamp, busses) = successfulParse text
  20       -- print timestamp
  21       -- print busses
  22       print $ part1 timestamp busses
  23       print $ part2 busses
  24
  25 part1 timestamp maybeBusses = eBus * eTime
  26   where busses = catMaybes maybeBusses
  27         busDepartures = map (busAndTime timestamp) busses
  28         (eBus, eTime) = head $ sortOn snd busDepartures
  29
  30 part2 maybeBusses = b - a
  31   where (a, b) = earliestGroup $ periodOffsets maybeBusses
  32
  33
  34 busAndTime timestamp period = (period, earliestDeparture timestamp period)
  35
  36 earliestDeparture timestamp period = period - (timestamp `mod` period)
  37
  38 periodOffsets :: [Maybe Integer] -> [(Integer, Integer)]
  39 periodOffsets maybeBusses = offsetBusses
  40   where offsetMaybeBusses = zip [0..] maybeBusses
  41         offsetJustBusses = filter (isJust . snd) offsetMaybeBusses
  42         offsetBusses = map (\(o, b) -> (o, fromJust b)) offsetJustBusses
  43
  44
  45 earliestGroup :: [(Integer, Integer)] -> (Integer, Integer)
  46 earliestGroup offsetBusses = foldl1 chineseStep offsetBusses
  47
  48
  49 chineseStep (n1, m1) (n2, m2) = (n, m1 * m2)
  50   where n = fromJust $ chinese (n1, m1) (n2, m2)
  51
  52
  53 -- Parse the input file
  54
  55 timeBusP = (,) <$> decimal <* endOfLine <*> busPeriodsP
  56
  57 busPeriodsP = busPeriodP `sepBy` (string ",")
  58
  59 busPeriodP = (Just <$> decimal) <|> ("x" *> pure Nothing)
  60
  61
  62 successfulParse :: Text -> (Integer, [Maybe Integer])
  63 successfulParse input =
  64   case parseOnly timeBusP input of
  65     Left  _err -> (0, []) -- TIO.putStr $ T.pack $ parseErrorPretty err
  66     Right timeBus -> timeBus