389. Find the Difference

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.

解题要点：

用XOR，详情看以下code。

class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        c = 0
        for i in s:
            c ^= ord(i)
        for j in t:
            c ^= ord(j)
        return chr(c)

找差值，在for loop里一定要先处理t再处理s。

class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        diff = 0
        for i in range(len(s)):          
            diff += ord(t[i])
            diff -= ord(s[i])
        diff += ord(t[-1])
        return chr(diff)