// Textbook fragment 08.13
/**
  * Realization of a priority queue by means of a heap.  A complete
  * binary tree realized by means of an array list is used to
  * represent the heap.
  */
public class HeapPriorityQueue<K,V> implements PriorityQueue<K,V> {
  protected CompleteBinaryTree<Entry<K,V>> heap;        // underlying heap
  protected Comparator<K> comp; // comparator for the keys
  /** Inner class for heap entries. */
  protected static class  MyEntry<K,V> implements Entry<K,V> {
    protected K key;
    protected V value;
    public MyEntry(K k, V v) { key = k; value = v; }
    public K getKey() { return key; }
    public V getValue() { return value; }
    public String toString() { return "(" + key  + "," + value + ")"; }
  }
  /** Creates an empty heap with the default comparator */
  public HeapPriorityQueue() {
    heap = new ArrayListCompleteBinaryTree<Entry<K,V>>(); // use an array list
    comp = new DefaultComparator<K>();     // use the default comparator
  }
  /** Creates an empty heap with the given comparator */
  public HeapPriorityQueue(Comparator<K> c) {
    heap = new ArrayListCompleteBinaryTree<Entry<K,V>>();
    comp = c;
  }
  /** Returns the size of the heap */
  public int size() { return heap.size(); }
  /** Returns whether the heap is empty */
  public boolean isEmpty() { return heap.size() == 0; }