389. Find the Difference

class Solution(object):

    def findTheDifference(self, s, t):

        """

        :type s: str

        :type t: str

        :rtype: str

        """

        dic,dif=collections.Counter(s),collections.Counter(t)

        for i in dif:

            if i not in dic or dic[i]!=dif[i]:

                return i
        return

返回不一样的元素