RepeatedSubstringPattern.java

/**
 * 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.
 *
 *
 * Constraints:
 *
 * 1 <= s.length <= 104
 * s consists of lowercase English letters.
 */

class Solution {
    public boolean repeatedSubstringPattern(String s) {
        int len = s.length();


        for(int i = 2; i <= len; i++){
            if(len % i == 0){
                String a = s.substring(0, len / i);
                StringBuilder sb = new StringBuilder();
                while(sb.length() < len) sb.append(a);
                if(sb.toString().equals(s)) return true;
            }
        }

        return false;
    }
}