2018/Day2/Day2B.hs

{-# LANGUAGE TupleSections #-}
module Day2B where
import Data.List (find)
import qualified Data.Sequence as S
import qualified Data.Foldable as F

dist' :: Int -> (S.Seq Char) -> String -> String -> (Int, String)
dist' n common (a:x) (b:y)
  | a == b    = dist' n (common S.|> a) x y
  | otherwise = dist' (n + 1) common x y
dist' n common _ _ = (n, F.toList common)

dist :: String -> String -> (Int, String)
dist = dist' 0 S.empty

combinations :: [String] -> [(String, String)]
combinations (x:xs) = map (x,) xs ++ combinations xs
combinations [] = []

distances :: [(String, String)] -> String
distances xs = result
  where Just(_, result) = find (\(x, _) -> x == 1) $ map (uncurry dist) xs

main :: IO ()
main = interact $ distances . combinations . lines