左旋转字符串

Question

直接字符串相加利用其自身的函数

public class Solution {
  public String LeftRotateString(String str,int n) {
    if(str == null) return "";
    int len = str.length();
    if (len == 0) return "";
    n = n % len;
    str += str;
    return str.substring(n,n+len);
  }
}