Cleanup (and apparently performance improvements)

Day2/Day2B.hs

@@ -1,25 +1,25 @@
 {-# LANGUAGE TupleSections #-}
 module Day2B where
-import Data.List (find)
+import Data.Maybe (mapMaybe)
-import qualified Data.Sequence as S
+import Data.Foldable (toList)
-import qualified Data.Foldable as F
+import qualified Data.Sequence as Seq
 
-dist' :: Int -> (S.Seq Char) -> String -> String -> (Int, String)
+distance' :: Int -> (Seq.Seq Char) -> String -> String -> Maybe String
-dist' n common (a:x) (b:y)
+distance' n common (a:x) (b:y)
-  | a == b    = dist' n (common S.|> a) x y
+  | a == b    = distance' n (common Seq.|> a) x y
-  | otherwise = dist' (n + 1) common x y
+  | otherwise = distance' (n + 1) common x y
-dist' n common _ _ = (n, F.toList common)
+distance' 1 common "" "" = Just(toList common)
+distance' _ _ _ _        = Nothing
 
-dist :: String -> String -> (Int, String)
+distance :: (String, String) -> Maybe String
-dist = dist' 0 S.empty
+distance (a, b) = distance' 0 Seq.empty a b
+
+distances :: [(String, String)] -> String
+distances xs = head $ mapMaybe distance xs
 
 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