LeetCode#344 Reverse String

key: traverse from backward
Runtime: 16 ms / beats 9.99%
No reference

class Solution {public:    string reverseString(string s) {        string res(s);        for(int i = s.size()-1; i>=0; i--)            res[s.size()-i-1] = s[i];        return res;    }};

Update: swap towards middle
Runtime: 12 ms / beats 28.49%
Reference:discuss

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