TheAlgorithms/Java · error · WordsToNumberException

INVALID_CONJUNCTION

INVALID_CONJUNCTION

Error message

Invalid Input. Incorrect 'and' placement

What it means

Thrown inside handleConjunction when the word deque is empty at the point 'and' is being processed — meaning 'and' was the last token in the input with no number following it. This is a structural error: English number grammar requires a number after 'and' (e.g., 'one hundred and five').

Source

Thrown at src/main/java/com/thealgorithms/conversions/WordsToNumber.java:129

    private static ArrayDeque<String> preprocessWords(String numberInWords) {
        String[] wordSplitArray = numberInWords.trim().split("[ ,-]");
        ArrayDeque<String> wordDeque = new ArrayDeque<>();
        for (String word : wordSplitArray) {
            if (word.isEmpty()) {
                continue;
            }
            wordDeque.add(word.toLowerCase());
        }
        if (wordDeque.isEmpty()) {
            throw new WordsToNumberException(WordsToNumberException.ErrorType.NULL_INPUT, "");
        }
        return wordDeque;
    }

    private static void handleConjunction(boolean prevNumWasHundred, boolean prevNumWasPowerOfTen, ArrayDeque<String> wordDeque) {
        if (wordDeque.isEmpty()) {
            throw new WordsToNumberException(WordsToNumberException.ErrorType.INVALID_CONJUNCTION, "");
        }

        String nextWord = wordDeque.pollFirst();
        String afterNextWord = wordDeque.peekFirst();

        wordDeque.addFirst(nextWord);

        Integer number = NumberWord.getValue(nextWord);

        boolean isPrevWordValid = prevNumWasHundred || prevNumWasPowerOfTen;
        boolean isNextWordValid = number != null && (number >= 10 || afterNextWord == null || "point".equals(afterNextWord));

        if (!isPrevWordValid || !isNextWordValid) {
            throw new WordsToNumberException(WordsToNumberException.ErrorType.INVALID_CONJUNCTION, "");
        }
    }

    private static BigDecimal handleHundred(BigDecimal currentChunk, String word, boolean prevNumWasPowerOfTen) {

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Ensure every 'and' is followed by a number word (ten through ninety-nine forms).
2. Trim trailing 'and' from input before conversion if it is spurious.
3. Validate the phrase structure with a regex or grammar check before calling convert.

Example fix

// before
WordsToNumber.convert('one hundred and');
// after
String s = input.trim();
if (s.endsWith(' and')) {
    throw new IllegalArgumentException('phrase cannot end with "and"');
}
WordsToNumber.convert(s);

static String sanitize(String s) {
    String t = s.trim();
    if (t.endsWith(" and") || t.equals("and")) throw new IllegalArgumentException("phrase cannot end with 'and'");
    return t;
}

static boolean endsWithConjunction(String s) {
    return s != null && s.trim().toLowerCase(Locale.ROOT).endsWith(" and");
}

try { WordsToNumber.convert(input); } catch (WordsToNumberException e) {
    if (e.errorType == ErrorType.INVALID_CONJUNCTION) throw new ApiException(400, "'and' must be followed by a number");
    throw e;
}

When it happens

Trigger: Input ending with 'and': convert('one hundred and'), convert('twenty and'). Also when trailing delimiters produce 'and' as the final token.

Common situations: Truncated user input; copy-paste that cuts off mid-phrase; voice-to-text that drops the trailing number; building phrases programmatically and forgetting the final operand.

Related errors

• UNEXPECTED_WORD
• MULTIPLE_NEGATIVES
• INVALID_NEGATIVE
• UNEXPECTED_WORD_AFTER_POINT
• MISSING_DECIMAL_NUMBERS

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/b509b1dfbfb77829. Report an issue: GitHub.