Begin Day 4, implement parser

[adventofcode2018.git] / day02 / boxes.hs

import qualified Data.Map as M

main :: IO ()
main = do
    input <- getContents
    let ids = lines input
    let count_twos = countN 2 ids
    let count_threes = countN 3 ids
    print (count_twos * count_threes)
    putStrLn . abc $ ids

countN :: Int -> [String] -> Int
countN check_count = sum . map (go check_count)
    where go :: Int -> String -> Int
          go cc test = if any (== cc) . M.elems . countChar $ test
                       then 1
                       else 0
          
countChar :: String -> M.Map Char Int
countChar = foldl go M.empty
    where go :: M.Map Char Int -> Char -> M.Map Char Int
          go chmap char = M.insert char ((M.findWithDefault 0 char chmap) + 1) chmap

abc :: [String] -> String
abc (i:is) 
    | null test = abc is
    | otherwise = head test
    where cor_len = (length i) - 1
          test = filter (\s -> (length s) == cor_len) . map (diff i) $ is

diff :: Eq a => [a] -> [a] -> [a]
diff [] [] = []
diff (a:as) (b:bs) 
    | a == b = (a : diff as bs)
    | otherwise = diff as bs