make books

        // TODO make books for this hand. Remove cards from the hand, and add one entry to the books list.
        // example: hand has 4 "6" values in, so a book of 6s. Remove all "6" from hand, and add one "6" to books.
        // example: hand starts as ["6","6","6","2","6","7"], books starts as ["4", "Q"]
        // After transfer, hand = ["2","7"] and books = ["4","Q","6"]

        // TODO comment your code!!!
        
        ArrayList<String> cardsToRemove = new ArrayList<>();
        for (String cardType : hand) {

           if (Collections.frequency(hand,cardType) == 4) {
               cardsToRemove.add(cardType);
           }


        }
        System.out.println("cards to remove " + cardsToRemove);
        
        if (cardsToRemove.size() > 0) {
            
            for (String c: cardsToRemove) {
                if (!books.contains(c)) books.add(c);
                
            }
        }

        hand.removeAll(cardsToRemove);
    
        System.out.println("books = " + books);
        System.out.println("hand = " + hand);

        }