我是菜鸟,我暂时没有考虑效率的问题,直接就为达目的不择手段了,能解决对我来说已经很不错了,等我经验多一点了,再考虑更多一些,请大家多多包涵,多多指正!

import java.util.*;
import java.lang.StringBuffer;
public class Solution {
    public String LeftRotateString(String str,int n) {
        String string = "";
        StringBuilder stringB = new StringBuilder(str);
        char c[] = str.toCharArray();
        if(c == null || c.length == 0){
           return "";     
        }
        for(int i = 0; i < n; i++){
            //deleteCharAt() 定位删除
            stringB.deleteCharAt(0);
            stringB.append(c[i]);
        }
        string = stringB.toString();
        return string;
    }
}