day02/boxes.hs

   1 import qualified Data.Map as M
   2
   3 main :: IO ()
   4 main = do
   5     input <- getContents
   6     let ids = lines input
   7     let count_twos = countN 2 ids
   8     let count_threes = countN 3 ids
   9     print (count_twos * count_threes)
  10     putStrLn . abc $ ids
  11
  12 countN :: Int -> [String] -> Int
  13 countN check_count = sum . map (go check_count)
  14     where go :: Int -> String -> Int
  15           go cc test = if any (== cc) . M.elems . countChar $ test
  16                        then 1
  17                        else 0
  18
  19 countChar :: String -> M.Map Char Int
  20 countChar = foldl go M.empty
  21     where go :: M.Map Char Int -> Char -> M.Map Char Int
  22           go chmap char = M.insert char ((M.findWithDefault 0 char chmap) + 1) chmap
  23
  24 abc :: [String] -> String
  25 abc (i:is)
  26     | null test = abc is
  27     | otherwise = head test
  28     where cor_len = (length i) - 1
  29           test = filter (\s -> (length s) == cor_len) . map (diff i) $ is
  30
  31 diff :: Eq a => [a] -> [a] -> [a]
  32 diff [] [] = []
  33 diff (a:as) (b:bs)
  34     | a == b = (a : diff as bs)
  35     | otherwise = diff as bs