package u6;

/**
 * Priority Queue.
 * Stores elements of the key-element pair type, where
 * the key is considered as a priority value.
 *
 * @author V.Boutchkova
 */
public interface PriorityQueue {
  
  /**
   * Inserts an element with priority key in this priority queue.
   * @param key the priority value; smaller keys represent greater priority.
   * @param element the element value;
   */
  public void insert(Object key, Object element);
  
  /**
   * Extracts the element with greater priority, i.e. with minimal key.
   * @return the element with minimal key
   */
  public Object extract();
  
  /**
   * Gets the number of entries in this priority queue.
   * @return the number of elements
   */
  public int size();
  
  /**
   * Checks whether this priority queue is empty. 
   * @return  true iff this priority queue is empty
   */
  public boolean isEmpty();
  
  /**
   * Reads the minimal key in this priority queue, 
   * without removing the element.
   */
  public Object minKey();
  
  /**
   * Reads the element with minimal key.
   */
  public Object minKeyElement();
}