docs: private static int postfixLen(String o1, String o2, int prefix) {
      int postfix = 0;
      int p1 = o1.length(), p2 = o2.length();
      while(p1 > prefix && p2 > prefix && (o1.charAt(--p1) == o2.charAt(--p2))) {
        ++postfix;
      }
      return postfix;
    }