459. Repeated Substring Pattern

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Problem

Given a string s, check if it can be constructed by taking a substring of it and appending multiple copies of the substring together.

Example 1:

Input: s = "abab"
Output: true
Explanation: It is the substring "ab" twice.

Example 2:

Input: s = "aba"
Output: false

Example 3:

Input: s = "abcabcabcabc"
Output: true
Explanation: It is the substring "abc" four times or the substring "abcabc" twice.

Code

class Solution {
    public boolean repeatedSubstringPattern(String s) {
        int len = s.length();
        
        for(int i = len / 2; i >= 1; i--) {
            if(len % i == 0) {
                int groupNum = len / i;
                String sub = s.substring(0, i);
                StringBuilder sb = new StringBuilder();
                
                for(int j = 0; j < groupNum; j++) {
                    sb.append(sub);
                }
                
                if(sb.toString().equals(s)) return true;
            }
        }
        
        return false;
    }
}