import java.util.Comparator;

/**
 * Abstract base class for priority queue implementations.  This 
 * gives the basic functions and interface required for a priority queue.
 * It might have been better done with an interface that had the methods
 * and have this class implement the interface (like the Java API does
 * with lists, maps, etc.) but that would have been overkill for the 
 * probably scope of usage this class will receive.
 */
public abstract class PriorityQueue {
	/**
	 * Constructs a new, empty priority queue according to the given 
	 * comparator. All objects inserted into the priority queue must
	 * be mutually comparable using the comparator c.
	 * 
	 * @param c	the comparator that will be used to order this queue.
	 */
	 public PriorityQueue(Comparator c) {
	 	comparator = c;
	 }

	/**
	 * Returns true if priority queue has no elements
	 *
	 * @return 	true if the priority queue has no elements
	 */
	public abstract boolean isEmpty();


	/**
	 * Returns a reference to the minimum element in the priority queue
	 *
	 * @return 	reference to the minimum element in the priority queue.
	 */
	public abstract Object findMin();

	/**
	 * Inserts a new object to the priority queue
	 *
	 * @param x	Object to be inserted into the priority queue.
	 */
	public abstract void insert(Object x);

	/**
	 * Removes the minimum element from the priority queue.
	 *
	 * @return 	reference to the minimum element.
	 */
	public abstract Object deleteMin();

	/**
	 * Erases all elements from the priority queue.
	 */
	public abstract void clear();

	/**
	 * Comparator used for ordering the elements in the priority queue.
	 */
	protected Comparator comparator;
}