每天一道剑指offer-左旋转字符串

public class Solution {
    public String LeftRotateString(String str,int n) {
        if(str == null || str.equals(""))
            return "";
        n = n % str.length();
        char [] strArray = str.toCharArray();
        reverse(strArray,0,str.length()-1);//反转整个字符串
        reverse(strArray,0,str.length()-n-1);//反转前字符串长度-n个字符
        reverse(strArray,str.length()-n,str.length()-1);//反转后n个字符
        return String.valueOf(strArray);
    }
    public void reverse(char [] strArray,int start,int end)
    {//反转字符数组
        while(start < end)
        {
            char ch = strArray[start];
            strArray[start] = strArray[end];
            strArray[end] = ch;
            start++;
            end--;
        }
    }
}