ArrayList<String> seen_author = new ArrayList();
int count=0;
for (int i = 0; i < numberOfBooks; i++){
	if(!seen_author.contains((book[i].getAuthor())){
		for (int j = i+1; j < numberOfBooks; j++){
			if (book[i].getWriter().equals(book[j].getWriter())) {
				count++;
           		}
      		}
		seen_author.add((book[i].getAuthor())
	}
}