public interface PriorityQueue {
     
    /**
 * A priority queue is a container of key-element pairs where the key stands for 
 * the element's priority in the queue when inserted. The priority queue has a 
 * removeMin method that gurantees that the object returned is associtaed with 
 * a key that is less than equal to all other keys in the tree. The order of
 * the keys is according to the natural ordering of its keys (see the Comparable interface), or by a 
 * comparator provided at creation time. 
 *  Apart from 1) A void (no arguments) constructor, which creates an empty priority queue sorted according to the natural order of its keys
 * 2. A constructor with a single argument of type Comparator, which creates an empty priority queue sorted according to the specified comparator. 
 *  <p>
 */

    /**
     Returns the number of key-element pairs in the priority queue.
    */
    public int size();
     /**
     *	    Returns true if and only if this queue contains no key-element pairs.
     */
    public boolean isEmpty();
    
    /**
     *	Insert an item with element <i>element</i> and key <i>key</i>
     *	into this dictionary.
     */
    public void insertItem(Object key, Object element);
    
    /**
     * Removes a key-element pair where, <it>(k,e)</it>, where <it>k</it> is
     * smaller or equal to all other keys i the priority queue.  It 
     * returns null if the priorityqueue is empty otherwise <it>e</it>. 
     */  
    public Object removeMin();

    /**
     * Returns an element,<it>e</it> with a key smaller than or equal to all other keys. It 
     * returns null if this priorityqueue is empty.
     */ 
    public Object minElement();
    /**
     * Returns a key,<it>k</it> that is smaller than or equal to all other keys. It 
     * returns null if this priorityqueue is empty.
     */ 
    public Object minKey();
      

}