LintCode（easy）旋转字符串（！！！我有史以来解决的问题最快的一次，心酸流泪）

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){        offset=offset%str.size();       string a = str.substr(str.size() - offset, offset);    str.erase(str.size() - offset, offset);    str = a + str;}else{}    }};