389. Find the Difference

题目摘要
给出两个只有小写字母的字符串s和t，t是由s中的字母随机排序并添加一个新字母得到的，找出那个新字母

解法
1. 初始化一个长度位26的整形数组，遍历(foreach)字符串s，++；再遍历字符串t，–，当–结果小于0时，返回遍历的当前的字符

public class Solution {    public char findTheDifference(String s, String t) {        int[] alpha = new int[26];        for (char c : s.toCharArray()) {            alpha[c - 'a']++;        }        for (char c : t.toCharArray()) {            if (--alpha[c - 'a'] < 0) {                return c;            }        }        return 0;    }}

1. 位操作

public class Solution {    public char findTheDifference(String s, String t) {        char c = t.charAt(t.length() - 1);        for (int i = 0; i < s.length(); i++) {            c ^= s.charAt(i);            c ^= t.charAt(i);        }        return c;    }}

注意
* ^=java会自动转换类型，如果 char = char ^ char ^ char;右边可能是int型,因为x ^ x = 0;

可问问题

原题
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.