new_contents: class Solution(object):
      def findTheDifference(self, s, t):
          """
          :type s: str
          :type t: str
          :rtype: str
          """
          s = list(s)
          for i in range(len(t)):
              try:
                  s.pop(s.index(t[i]))
              except ValueError:
                  return t[i]
  
subject: Solve task #389