class Solution(object):

def findTheDifference\(self, s, t\):

    """

    :type s: str

    :type t: str

    :rtype: str

    """

    letters = \[0\] \* 26

    for c in s:

        letters\[ord\(c\) - 97\] += 1

    for c in t:

        letters\[ord\(c\) - 97\] -= 1

        if letters\[ord\(c\) - 97\] < 0:

            return c

可以设成dict