AoC2018/Day2/Part2.hs

24 lines
725 B
Haskell
Executable File

#! /usr/bin/env stack
-- stack --resolver lts-12.20 --install-ghc script
module Main where
loopRight :: b -> (b -> Either a b) -> a
loopRight b f = case f b of
Left a -> a
Right b' -> loopRight b' f
main :: IO ()
main = interact $ show . \input ->
let codes = lines input :: [[Char]]
in loopRight ([], codes) $ \(seen, c:cs) ->
case filter (`isSimilarTo` c) seen of
[] -> Right (c:seen, cs)
(x:_) -> Left (c, x, foldMap (\(a,b) -> if a == b then [a] else [])
(zip c x))
isSimilarTo :: (Eq a) => [a] -> [a] -> Bool
(x:xs) `isSimilarTo` (y:ys)
| x == y = xs `isSimilarTo` ys
| otherwise = xs == ys
_ `isSimilarTo` _ = False