advent02/src/advent02.hs

   1 -- import Debug.Trace
   2
   3 import Data.Text (Text)
   4 import qualified Data.Text.IO as TIO
   5
   6 import Data.Void (Void)
   7
   8 import Text.Megaparsec hiding (State)
   9 import Text.Megaparsec.Char
  10 import qualified Text.Megaparsec.Char.Lexer as L
  11 import qualified Control.Applicative as CA
  12
  13 data Policy = Policy
  14   { lower :: Int
  15   , upper :: Int
  16   , character :: Char
  17   , password :: String
  18   } deriving (Show, Eq, Ord)
  19
  20 main :: IO ()
  21 main =
  22   do  text <- TIO.readFile "data/advent02.txt"
  23       let policies = successfulParse text
  24       print $ part1 policies
  25       print $ part2 policies
  26
  27 part1 = length . filter inRange
  28   where nCharsPresent p = length $ filter (== (character p)) (password p)
  29         inRange p = (nCharsPresent p >= (lower p)) && (nCharsPresent p <= (upper p))
  30
  31 part2 = length . filter matches
  32
  33 matches p = ((pw!!l) == c) /= ((pw!!u) == c)
  34   where pw = password p
  35         c = character p
  36         l = (lower p) - 1
  37         u = (upper p) - 1
  38
  39
  40 -- Parse the input file
  41 type Parser = Parsec Void Text
  42
  43 sc :: Parser ()
  44 sc = L.space (skipSome spaceChar) CA.empty CA.empty
  45 -- sc = L.space (skipSome (char ' ')) CA.empty CA.empty
  46
  47 lexeme  = L.lexeme sc
  48 integerP = lexeme L.decimal
  49 -- signedInteger = L.signed sc integer
  50 symb = L.symbol sc
  51 hyphenP = symb "-"
  52 colonP = symb ":"
  53 characterP = alphaNumChar <* sc
  54 passwordP = some alphaNumChar <* sc
  55
  56 policiesP = many policyP
  57 policyP = Policy <$> integerP <* hyphenP <*> integerP <*> characterP <* colonP <*> passwordP
  58
  59 successfulParse :: Text -> [Policy]
  60 successfulParse input =
  61   case parse policiesP "input" input of
  62     Left  _err -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
  63     Right policies -> policies