逆转字符串Reverse String

https://leetcode.com/problems/reverse-string/

class Solution {public:    string reverseString(string s) {        int len = s.size();        if (len <= 1){            return s;        }        int i = 0, j = len - 1;        while (i < j){            swap(s[i], s[j]);            i++;            j--;        }        return s;    }};