aoc2020/day6.hs

import Data.List (nub)

main :: IO ()
main = do
  raw <- readFile "day6.txt"
  let ls = map concat $ split "" $ lines raw
      ms = split "" $ lines raw
      ansA = sum $ map (length . nub) ls
      ansB = sum $ map (length . (foldr match ['a'..'z'])) ms
   in do 
     putStrLn $ "day6a: " ++ (show ansA)
     putStrLn $ "day6b: " ++ (show ansB)

match :: Ord a => [a] -> [a] -> [a]
match as bs = nub $ filter (`elem` bs) as

split :: Eq a => a -> [a] -> [[a]]
split _ [] = []
split d as = chunk : (split d rest)
  where
    chunk = takeWhile (/= d) as
    rest = drop 1 $ dropWhile (/= d) as