2019-02-05 Day 31

1.反转字符串
编写一个函数，其作用是将输入的字符串反转过来。输入字符串以字符数组 char[] 的形式给出。

不要给另外的数组分配额外的空间，你必须原地修改输入数组、使用 O(1) 的额外空间解决这一问题。

你可以假设数组中的所有字符都是 ASCII 码表中的可打印字符。

示例 1：

">输入：["h","e","l","l","o"]
输出：["o","l","l","e","h"]

示例 2：

输入：["H","a","n","n","a","h"]
输出：["h","a","n","n","a","H"]

class Solution {
public:
    void reverseString(vector<char>& s) {
        
        int head = 0, end = s.size() - 1;
       
        while( head < end )
        {
            s[head] = s[head] ^ s[end];
            s[end] = s[head] ^ s[end];
            s[head] = s[head] ^ s[end];
            
            head ++;
            end --;
        }
        
        
    }
};