230327 브라이언의 고민

private static final String INVALID = "invalid";

private String rule1(String str) {
    StringBuilder ret = new StringBuilder();
    if (str.length() < 3) {
        return "-1";
    }
    char c = str.charAt(1);
    boolean ok = false;
    for (int i = 0; i < str.length(); i++) {
        if (Character.isLowerCase(str.charAt(i))) {
            ok = true;
        }
        if (i % 2 == 0) {
            if (Character.isLowerCase(str.charAt(i))) {
                return "-1";
            }
            ret.append(str.charAt(i));
        } else {
            if (c != str.charAt(i)) {
                return "-1";
            }
        }
    }
    if (!ok) {
        return "-1";
    }
    return ret.toString();
}

private String allUpper(String str) {
    StringBuilder ret = new StringBuilder();
    for (char c : str.toCharArray()) {
        if (!Character.isUpperCase(c)) {
            return "-1";
        }
        ret.append(c);
    }
    return ret.toString();
}

public String solution(String sentence) {
    boolean[] used = new boolean[26];
    StringBuilder answer = new StringBuilder();
    while (!sentence.isEmpty()) {
        String ret;
        List<Integer> pos = new ArrayList<>();
        if (Character.isLowerCase(sentence.charAt(0))) {
            if (used[sentence.charAt(0) - 'a']) {
                return INVALID;
            }
            used[sentence.charAt(0) - 'a'] = true;
            for (int i = 0; i < sentence.length(); i++) {
                if (sentence.charAt(i) == sentence.charAt(0)) {
                    pos.add(i);
                }
            }
            if (pos.size() != 2) {
                return INVALID;
            }

            String center = sentence.substring(1, pos.get(pos.size() - 1));
            if (center.isEmpty()) {
                return INVALID;
            }
            ret = rule1(center);
            if (ret.equals("-1")) {
                ret = allUpper(center);
                if (ret.equals("-1")) {
                    return INVALID;
                }
            } else {
                if (used[sentence.charAt(2) - 'a']) {
                    return INVALID;
                }
                used[sentence.charAt(2) - 'a'] = true;
            }
            sentence = sentence.substring(pos.get(pos.size() - 1) + 1);
        } else {
            if (sentence.length() == 1 || Character.isUpperCase(sentence.charAt(1))) {
                ret = String.valueOf(sentence.charAt(0));
                sentence = sentence.substring(1);
            } else {
                for (int i = 0; i < sentence.length(); i++) {
                    if (sentence.charAt(1) == sentence.charAt(i)) {
                        pos.add(i);
                    }
                }

                if (pos.size() != 2) {
                    if (pos.get(pos.size() - 1) == sentence.length() - 1) {
                        return INVALID;
                    }
                    if (Character.isLowerCase(sentence.charAt(pos.get(pos.size() - 1) + 1))) {
                        return INVALID;
                    }
                    String center = sentence.substring(0, pos.get(pos.size() - 1) + 2);
                    ret = rule1(center);
                    if (ret.equals("-1")) {
                        return INVALID;
                    }
                    if (used[sentence.charAt(1) - 'a']) {
                        return INVALID;
                    }
                    used[sentence.charAt(1) - 'a'] = true;
                    sentence = sentence.substring(pos.get(pos.size() - 1) + 2);
                } else {
                    ret = sentence.charAt(0) + "";
                    sentence = sentence.substring(1);
                }
            }
        }
        answer.append(ret + " ");
    }
    answer.delete(answer.length()-1, answer.length());
    return answer.toString();
}