思路

方法：首尾双指针

 1 class Solution {
 2 public:
 3     void reverseString(vector<char>& s) {
 4         int i = 0, j = s.size()-1;
 5         while(i < j) {
 6             swap(s[i], s[j]);
 7             ++i;
 8             --j;
 9         }
10     }
11 };