6b.hs

import Data.List
import Prelude

main = do
  input <- getContents
  putStr $ show $ fn input

groupAnswer :: [String] -> [[String]]
groupAnswer = map (filter ("" /=)) . groupBy (\_ y -> y /= "")

mergeAnswer :: [String] -> (Int, String)
mergeAnswer ys = (length ys, unwords ys)

countOccurances :: Eq a => [a] -> a -> Int
countOccurances xs y = length $ filter (y ==) xs

-- This does, right to left:

-- $ create a list of unique items from the answers

-- $ map the unique items, replace each of them with the count of them in the original list

-- $ filter where the count is equal to the amount of group members (ie. 3 people answered, filter the items where all 3 did for that specific answer)
-- check length

checkAnswer :: (Int, String) -> Int
checkAnswer (count, answers) = length $ filter (count ==) $ map (countOccurances answers) $ nub answers

fn :: String -> Int
fn xs = sum $ map (checkAnswer . mergeAnswer) $ groupAnswer $ lines xs