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import Data.List
main :: IO ()
main = do
input <- readFile "input"
putStrLn . formatOutput . both (sum . map length) . groups . map lines . dlfsplit $ input
formatOutput :: Show a => (a, a) -> String
formatOutput (part1,part2) = "Part 1: " ++ show part1 ++ "\nPart 2: " ++ show part2
-- Collect each group's answers
groups :: (Foldable t, Eq a) => [t [a]] -> ([[a]], [[a]])
groups [] = ([],[])
groups (g:gs) = (foldr1 union g : unions, foldr1 intersect g : intersections)
where (unions, intersections) = groups gs
-- Split a string into a list across all the double newlines in it
dlfsplit :: String -> [String]
dlfsplit str = a : case b of
[] -> []
b -> dlfsplit b
where (a,b) = dlfsplitonce str
-- Split a string into two across the first double newline found
dlfsplitonce :: String -> (String, String)
dlfsplitonce [] = ([], [])
dlfsplitonce (ca:cb:rest)
| ca == '\n' && cb == '\n' = ([], rest)
| otherwise = (ca:before, after)
where (before, after) = dlfsplitonce (cb : rest)
dlfsplitonce c = (c, [])
-- Apply a function to both parts of a pair
both :: (a -> b) -> (a, a) -> (b, b)
both f (a,b) = (f a, f b)