private static String generateHeuristicPastParticiple(String verb) {
    int length = verb.length();
    char c1 = toLowerCase(verb.charAt(length - 1));
    if (c1 == 'e') return verb + 'd';
    char c2 = toLowerCase(verb.charAt(length - 2));
    if (c1 == 'y' && !isVowel(c2)) return verb.substring(0, length - 1) + "ied";
    return c1 == 'c' && isVowel(c2) ? verb + "ked" : verb + "ed";
  }
private static String generateHeuristicPastParticiple(String verb)