左旋转字符串

class Solution {
public:
string reverse(string str,int i,int j)
{
while(i<j)
{
char tmp=str[j];
str[j]=str[i];
str[i]=tmp;
i++;j--;
}
return str;
}
string LeftRotateString(string str, int n) {
string s;
if(str.empty())
return s;
if(n>str.size())return s;
s=reverse(str,0,str.size()-1);
s=reverse(s,0,s.size()-n-1);
s=reverse(s,s.size()-n,s.size()-1);
return s;
}
};