private List<Card> findPossibleCards(List<Card> cardList, int rowNumber) {
        List<Card> result = new ArrayList<>();
        if ((rowNumber > 4)||(rowNumber < 1)) {
            throw new IllegalArgumentException();
        }
        int rowIndex = rowNumber - 1;
        for (int columnIndex = 0; columnIndex < 4; columnIndex++) {
            result.add(cardList.get(4*rowIndex + columnIndex));
        }
        return result;
    }