Adds solution 2

2/2.hs

@@ -0,0 +1,13 @@
+module Main where
+
+import Data.List (group, sort)
+
+main = do
+  ids <- lines <$> getContents
+  print (length (repeatCounts 2 ids) * length (repeatCounts 3 ids))
+
+  let (a, b) = head [(x, y) | x <- ids, y <- ids, countDiffChars x y == 1]
+  print $ filter (/= '!') $ zipWith (\x y -> if x == y then x else '!') a b
+  where
+    repeatCounts x = filter (x `elem`) . map (map length . group . sort)
+    countDiffChars as bs = sum $ zipWith (\a b -> if a == b then 0 else 1) as bs