[leetcode: Python]389. Find the Difference

题目：
Given two strings s and t which consist of only lowercase letters.

String t is generated by random shuffling string s and then add one more letter at a random position.

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

方法一：性能46ms

class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        res = ord(t[-1])
        for i in range(len(s)):
            res += ord(t[i]) - ord(s[i])
        return chr(res)

方法二：性能39ms

class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """

        a=ord(t[0])

        for i in s+t[1:]:
            a=a^ord(i)
        return chr(a)