左旋转字符串

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