package java.util;

public class HashSet<T> implements Set<T> {
  private static final Object Value = new Object();

  private final HashMap<T, Object> map;

  public HashSet(int capacity) {
    map = new HashMap(capacity);
  }

  public HashSet() {
    this(0);
  }

  public int size() {
    return map.size();
  }

  public boolean contains(T element) {
    return map.containsKey(element);
  }

  public boolean add(T element) {
    return map.put(element, Value) != Value;
  }

  public boolean remove(T element) {
    return map.remove(element) != Value;
  }

  public void clear() {
    map.clear();
  }

  public Iterator<T> iterator() {
    return new MyIterator(map.iterator());
  }

  private static class MyIterator<T> implements Iterator<T> {
    private final Iterator<Map.Entry<T, Object>> it;

    public MyIterator(Iterator<Map.Entry<T, Object>> it) {
      this.it = it;
    }

    public T next() {
      return it.next().getKey();
    }

    public boolean hasNext() {
      return it.hasNext();
    }

    public void remove() {
      it.remove();
    }
  }
}