459. Repeated Substring Pattern

Given a non-empty string check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. You may assume the given string consists of lowercase English letters only and its length will not exceed 10000.

Example 1:

Input: "abab" Output: True Explanation: It's the substring "ab" twice.

Example 2:

Input: "aba" Output: False

Example 3:

Input: "abcabcabcabc" Output: True Explanation: It's the substring "abc" four times. (And the substring "abcabc" twice.)

class Solution {

   public boolean repeatedSubstringPattern(String str) {

        int len = str.length(); //设str是ababab，则len为6

        for(int i = len/2 ; i >= 1 ; i--) { //i从3开始

            if(len % i == 0) {

                int m = len / i; //说明str中有m个子数组

                String subS = str.substring(0,i);

                int j;

                for (j = 1; j < m; j++) {

                    if(!subS.equals(str.substring(j * i,i + j * i))) 

                   break; //！！！注意这个break只跳出内循环

                }

                if (j == m)

                   return true;

           }

       }

       return false;

    }

}