public List<Book> getValidCombination(List<Book> books, List<Vote> votes) {
		List<Book> listBookFiltered = new ArrayList<Book>();
		
		if (books == null) {
			return null;
		}

		//baguncar lista para animar a brincadeira
		Collections.shuffle(books);
		
		for (Book book1 : books) {

			for (Book book2 : books) {

				if (!isVoted(book1, book2, votes)) {
					if(book1.equals(book2)){
						continue;
					}
					listBookFiltered.add(book1);
					listBookFiltered.add(book2);
					return listBookFiltered;
				}

			}

		}

		return null;
	}