import java.util.*;

public class MySet extends AbstractSet {
	private Object[] elements;
	private int size;
	private final int INITIAL_CAPACITY = 10;
	
	/**
	  * Default constructor
	  */
	public MySet() {
		elements = new Object[INITIAL_CAPACITY];
		size = 0;
	} // end constructor
	
	/**
	  * Constructor from a Collection
	  */
	public MySet(Collection c) {
		elements = new Object[c.size()];
		size = 0;
		Iterator cItr = c.iterator();
		while( cItr.hasNext() ) {
			add(cItr.next());
		} // end while
	} // end constructor
	
	/**
	  * Ensures that this set contains the specified element
	  * @returns true if this set is modified
	  */
	public boolean add(Object x) {
		if( contains(x) ) return false;
		if( size == elements.length) resize();
		elements[size++] = x;
		return true;
	} // end add
	
	/**
	  * Returns the number of elemenst in this set
	  * @return the number of elements in this set
	  */
	public int size() {
		return size;
	} // end size
	
	/**
	  * Returns an iterator over the elements in this set
	  * @return an Iterator over the elemenst in this set
	  */
	public Iterator iterator() {
		return new MyIterator();
	}
	
	private class MyIterator implements Iterator {
		private int current;
		private boolean removeOK;
		
		public MyIterator() {
			current = 0;
			removeOK = false;
		} // end constructor
		
		public boolean hasNext() {
			return current < size;
		}// end hasNext
		
		public Object next() {
			if( !hasNext() ) throw new NoSuchElementException();
			removeOK = true;
			return elements[current++];
		} // end next
		
		public void remove() {
			if( !removeOK ) throw new IllegalStateException();
			for( int i = current; i < size; i++ ) {
				elements[i-1] = elements[i];
			} // end for
			size--;
			current--;
			removeOK = false;
		} // end remove
		
	} // end MyIterator
	
	private void resize() {
		Object[] save = elements;
		elements = new Object[2*save.length+1];
		for( int i = 0; i < size; i++ ) {
			elements[i] = save[i];
		} // end for
	} // end resize
	
} // end MySet