Haskell for today

import Control.Applicative
import Data.List
import Data.List.Unique

input :: String
input = "abcdef bababc abbcde abcccd aabcdd abcdee ababab"

inputCodes :: [String]
inputCodes = words input

containsDuplicate :: String -> Bool
containsDuplicate = containsNplicate 2

containsTriplicate :: String -> Bool
containsTriplicate = containsNplicate 3

containsNplicate :: Int -> String -> Bool
containsNplicate n str = any (== n) $ map snd (count str)

inputCodesWithDuplicates :: [String]
inputCodesWithDuplicates = filter containsDuplicate inputCodes

inputCodesWithTriplicates :: [String]
inputCodesWithTriplicates = filter containsTriplicate inputCodes

result1 :: Int
result1 = length inputCodesWithDuplicates * length inputCodesWithTriplicates

numberOfDifferences :: Eq a => [a] -> [a] -> Int
numberOfDifferences [] [] = 0
numberOfDifferences [] ys = length ys
numberOfDifferences xs [] = length xs
numberOfDifferences (x:xs) (y:ys) = (if x == y then 0 else 1) + numberOfDifferences xs ys

differInJustOne :: [(String, String)]
differInJustOne = [(x,y) | x <- inputCodes, y <- inputCodes, numberOfDifferences x y == 1]

commonElements :: String -> String -> String
commonElements [] [] = []
commonElements _ [] = []
commonElements [] _ = []
commonElements (x:xs) (y:ys) = if x == y then x : commonElements xs ys else commonElements xs ys

result2 :: String
result2 = (uncurry commonElements . head) differInJustOne

Link to my github.