aoc2020/day6.hs

import Data.List (nub, sort)

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, Eq a) => [a] -> [a] -> [a]
match as bs = (sort . nub) $ filter (`elem` bs) as

split :: Eq a => a -> [a] -> [[a]]
split _ [] = []
split v as = split' v as [] []

split' :: Eq a => a -> [a] -> [a] -> [[a]] -> [[a]]
split' _ [] a as = as ++ [a]
split' v (b:bs) a as
  | b == v = split' v bs [] (as ++ [a])
  | otherwise = split' v bs (a ++ [b]) as