leetcode 344:反转字符串

题目:

算法思想：双下标即可。

代码：

    void reverseString(vector<char>& s) {
        int a = 0;
        int b = s.size()-1;
        while(a <= b)
        {
            char tmp = s[a];
            s[a] = s[b];
            s[b] = tmp;
            a++;
            b--;
        }
    }