左旋转字符串_43

public String LeftRotateString(String str,int n) {
        //左移位数确定
        int length=str.length();
        if (length==n||n==0||length<1){
            return str;
        }
        n%=length;

        //保留第n个字符到末尾再加上前n个字符
        str+=str;
        return str.substring(n,length+n);
    }