[Leetcode从零开刷]389. Find the Difference

题目来源
leetcode
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:eExplanation:'e' is the letter that was added.

翻译：给你两个字符串s和t，只包含小写字母，其中t是s的随机排列，其中在任意位置还增加了一个字母，题目就是找到这个字母。
cpp

class Solution {public:    char findTheDifference(string s, string t) {        char r=0;        for(char c:s) r ^=c;        for(char c:t) r ^=c;        return r;    }};

首先：
1 0^1 1 = 0 1
a^b = b^a
a^a = 0
则遍历s :0^a^b^c^d 为r
再遍历t:0^a^b^c^d ^a^b^c^d^e = e
简言之
先用0异或遍历s的每个元素变成r,再用r和遍历t的每个元素，返回r即是两者不同的地方。