OJ lintcode 旋转字符串

给定一个字符串和一个偏移量，根据偏移量旋转字符串(从左向右旋转)
您在真实的面试中是否遇到过这个题？
Yes
样例
对于字符串 "abcdefg".
offset=0 => "abcdefg"
offset=1 => "gabcdef"
offset=2 => "fgabcde"
offset=3 => "efgabcd"

class Solution {
public:
    /**
    * @param str: a string
    * @param offset: an integer
    * @return: nothing
    */
    void rotateString(string &str, int offset) {
        //wirte your code here
        if(str.size()==0){
            return ;
        }
        if (offset == 0 || offset % str.length()==0) {
            return ;
        }
        if (offset > str.length()) {
            offset = offset%str.length();
        }
        int newbegin = str.length() - offset;
        int newend = str.length();

        string res(str.begin()+newbegin, str.end());
        string res1(str.begin(), str.begin() + newbegin);

        //res.insert(str.end(), str.begin(), str.begin() + newbegin);
        str = res+res1;
    }
};