剑指 Offer 58 - II. 左旋转字符串

public String reverseLeftWords(String s, int n) {
        int len = s.length();
        n = n%len;
        String sub_str1 = s.substring(0,n);
        String sub_str2 = s.substring(n);
        return sub_str2+sub_str1;
    }