剑指offer43：左旋转字符串（字符串）：对于一个给定的字符序列S，请你把其循环左移K位后的序列输出。

1 class Solution {
2 public:
3     string LeftRotateString(string str, int n) {
4         string str1;
5         str1 = str.substr(0,n);
6         str.erase(0,n);
7         return str+str1;
8     }
9 };

 1 class Solution {
 2 public:
 3     string LeftRotateString(string str, int n) {
 4         if (n>str.size()||n<0)return "";
 5         if (n == str.size()||n==0)return str;
 6         string s1, s2;
 7         for (int i = 0; i < str.size();i++)
 8             if (i < n)
 9                 s1 += str[i];
10             else 
11                 s2 += str[i];
12         return s2 + s1;
13     }
14 };