左旋转字符串

 1 class Solution {
 2 public:
 3     string reverse(string str,int i,int j)
 4         {
 5         while(i<j)
 6              {
 7              char tmp=str[j];
 8             str[j]=str[i];
 9             str[i]=tmp;
10             i++;j--;
11          }
12         return str;
13     }
14     string LeftRotateString(string str, int n) {
15         string s;
16        if(str.empty())
17            return s;
18         if(n>str.size())return s;
19         s=reverse(str,0,str.size()-1);
20         s=reverse(s,0,s.size()-n-1);
21         s=reverse(s,s.size()-n,s.size()-1);
22         return s;
23     }
24 };