Adds solution 2

2/2.hs

@@ -0,0 +1,14 @@
+module Main where
+
+import Data.List (group, sort)
+
+main = do
+  ids <- lines <$> getContents
+  print (length (repeatCounts 2 ids) * length (repeatCounts 3 ids))
+
+  let diff = head [ diff | x <- ids, y <- ids
+                         , let diff = zipWith (\ a b -> if a == b then a else '!') x y
+                         , length (filter (== '!') diff) == 1 ]
+  print $ filter (/= '!') diff
+  where
+    repeatCounts x = filter (x `elem`) . map (map length . group . sort)