advent14.hs

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