advent05.hs

   1 module Main(main) where
   2
   3 import Data.Hash.MD5 (md5s, Str(..))
   4 import Data.List (isPrefixOf)
   5 import qualified Data.Map.Lazy as Map
   6
   7 type Password = Map.Map Integer Char
   8
   9 input = "cxdnnyjw"
  10
  11 main :: IO ()
  12 main = do
  13         part1
  14         part2
  15
  16
  17 part1 :: IO ()
  18 part1 = do
  19     print $ take 8 [h!!5 | h <- filter (interesting) $ md5sequence input 0]
  20
  21 part2 :: IO ()
  22 part2 = do
  23     print $ Map.foldr (:) [] password
  24     where interestingHashes =
  25             [(read [h!!5], h!!6) |
  26               h <- filter (interesting) (md5sequence input 0),
  27               h!!5 `elem` "01234567"]
  28           password = findPassword Map.empty interestingHashes
  29
  30
  31 md5sequence :: String -> Integer -> [String]
  32 md5sequence key i = (md5s (Str (key ++ show i))) : (md5sequence key (i+1))
  33
  34 interesting :: String -> Bool
  35 interesting hash = "00000" `isPrefixOf` hash
  36
  37 dontReplace :: (Integer, Char) -> Password -> Password
  38 dontReplace (k, v) = Map.insertWith (\_ v -> v) k v
  39
  40 findPassword :: Password -> [(Integer, Char)] -> Password
  41 findPassword p (c:cs)
  42   | Map.size p == 8 = p
  43   | otherwise = findPassword p' cs
  44       where p' = dontReplace c p