| import java.util.ArrayList; |
| import java.util.HashMap; |
| import java.util.List; |
| import java.util.Map; |
| import java.util.Optional; |
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| public class Library { |
| public static final int MAX_LOANS = 3; |
| private final Map<String, String> titles = new HashMap<>(); |
| private final Map<String, String> loans = new HashMap<>(); |
|
|
| public boolean addBook(String isbn, String title) { |
| if (isbn == null || isbn.isBlank() || title == null || title.isBlank()) { |
| throw new IllegalArgumentException("isbn and title are required"); |
| } |
| return titles.putIfAbsent(isbn, title) == null; |
| } |
|
|
| public void borrow(String isbn, String member) { |
| if (!titles.containsKey(isbn)) { |
| throw new java.util.NoSuchElementException("unknown book: " + isbn); |
| } |
| if (loans.containsKey(isbn)) { |
| throw new IllegalStateException("already borrowed"); |
| } |
| if (borrowedBy(member).size() >= MAX_LOANS) { |
| throw new IllegalStateException("loan limit reached"); |
| } |
| loans.put(isbn, member); |
| } |
|
|
| public Optional<String> giveBack(String isbn) { |
| return Optional.ofNullable(loans.remove(isbn)); |
| } |
|
|
| public List<String> borrowedBy(String member) { |
| List<String> out = new ArrayList<>(); |
| for (Map.Entry<String, String> e : loans.entrySet()) { |
| if (e.getValue().equals(member)) { |
| out.add(e.getKey()); |
| } |
| } |
| out.sort(String::compareTo); |
| return out; |
| } |
|
|
| public boolean isAvailable(String isbn) { |
| return titles.containsKey(isbn) && !loans.containsKey(isbn); |
| } |
|
|
| public int bookCount() { |
| return titles.size(); |
| } |
| } |
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