Find the different

# https://leetcode.com/problems/find-the-difference/description/
# aka: remove all duplicated elements
# idea: a XOR a = 0
class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        return chr(reduce(operator.xor, map(ord, s + t)))