repeated substring

import java.util.*;

public class Solution {
  public boolean repeatedSubstringPattern(String str) {
    int length = str.length();
    if (length <= 1) return false;

    List<Integer> factors = new ArrayList();
    // Factor
    for (int i = 1; i * 2 <= length; ++i) {
      if (length % i == 0) {
        factors.add(i);
        factors.add(length / i);
      }
    }
    Collections.sort(factors);
    Collections.reverse(factors);
    factors.remove(0);
    HashSet<Integer> uniqueFactors = new HashSet<Integer>();

    for (Integer n : factors) {
      uniqueFactors.add(n);
    }

    for (Integer possibleLength : factors) {
      String sub = str.substring(0, possibleLength);
      boolean works = true;
      for (int i = possibleLength; i <= str.length() - possibleLength; i += possibleLength) {
        String sub2 = str.substring(i, i + possibleLength);
        if (!str.substring(i, i + possibleLength).equals(sub)) {
          works = false;
          break;
        }
      }
      if (works) { return works; }
    }

    return false;
  }
}