advent14c.hs

   1 import Data.List (nub, tails, null)
   2 import Data.Hash.MD5 (md5s, Str(..))
   3
   4 import Data.ByteString.Char8 (pack)
   5 import Crypto.Hash (hash, Digest, MD5)
   6
   7 salt = "yjdafjpo"
   8 -- salt = "abc"
   9
  10 main :: IO ()
  11 main = do
  12         part1
  13         part2
  14
  15
  16 part1 :: IO ()
  17 part1 = print $ head $ drop 63 $ filter (\i -> possibleStart sq i && confirmStart sq i) [0..]
  18     where sq = md5sequence
  19
  20 part2 :: IO ()
  21 part2 = print $ head $ drop 63 $ filter (\i -> possibleStart sq i && confirmStart sq i) [0..]
  22     where sq = md5sequenceS
  23
  24
  25 getHash :: String -> String
  26 getHash bs = show (hash $ pack bs :: Digest MD5)
  27
  28 md5sequence :: [String]
  29 md5sequence = [makeMd5 i | i <- [0..]]
  30     where makeMd5 i = getHash (salt ++ show i)
  31
  32 md5sequenceS :: [String]
  33 md5sequenceS = [makeMd5 i | i <- [0..]]
  34     where makeMd5 i = stretch $ md5s (Str (salt ++ show i))
  35           stretch h0 = foldr (\_ h -> getHash h) h0 [1..2016]
  36
  37 possibleStart :: [String] -> Int-> Bool
  38 -- possibleStart s i = not $ null $ repeats 3 $ s!!i
  39 possibleStart s = not . null . repeats 3 . ((!!) s)
  40
  41 confirmStart :: [String] -> Int -> Bool
  42 confirmStart s i = any (confirmation) $ take 1000 $ drop (i+1) s
  43     where c = head $ repeats 3 $ s!!i
  44           confirmation m = c `elem` (repeats 5 m)
  45
  46
  47 repeats :: Int -> String -> [String]
  48 repeats n = filter (null . tail) . map (nub) . substrings n
  49
  50 substrings :: Int -> [a] -> [[a]]
  51 substrings l = filter (\s -> (length s) == l) . map (take l) . tails
  52