data_structures_free

net/datastructures/HeapPriorityQueue.java

@@ -0,0 +1,128 @@
+package net.datastructures;
+import java.util.Comparator;
+
+//begin#fragment HeapPriorityQueue
+/** 
+  * 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.
+//end#fragment HeapPriorityQueue
+  *
+  * @author Roberto Tamassia, Michael Goodrich, Eric Zamore
+//begin#fragment HeapPriorityQueue
+  */
+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;
+  }
+//end#fragment HeapPriorityQueue
+  /** Sets the comparator used for comparing items in the heap. 
+   * @throws IllegalStateException if priority queue is not empty */
+  public void setComparator(Comparator<K> c) throws IllegalStateException {
+    if(!isEmpty())  // this is only allowed if the priority queue is empty
+      throw new IllegalStateException("Priority queue is not empty");
+    comp = c;
+  }
+//begin#fragment HeapPriorityQueue
+  /** 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; }
+  //end#fragment HeapPriorityQueue
+  //begin#fragment mainMethods
+  /** Returns but does not remove an entry with minimum key */
+  public Entry<K,V> min() throws EmptyPriorityQueueException {
+    if (isEmpty()) 
+      throw new EmptyPriorityQueueException("Priority queue is empty");
+    return heap.root().element();
+  }
+  /** Inserts a key-value pair and returns the entry created */
+  public Entry<K,V> insert(K k, V x) throws InvalidKeyException {
+    checkKey(k);  // may throw an InvalidKeyException
+    Entry<K,V> entry = new MyEntry<K,V>(k,x);
+    upHeap(heap.add(entry));
+    return entry;
+  }
+  /** Removes and returns an entry with minimum key */
+  public Entry<K,V> removeMin() throws EmptyPriorityQueueException {
+    if (isEmpty()) 
+      throw new EmptyPriorityQueueException("Priority queue is empty");
+    Entry<K,V> min = heap.root().element();
+    if (size() == 1)
+      heap.remove();
+    else {
+      heap.replace(heap.root(), heap.remove());
+      downHeap(heap.root());
+    }
+    return min;
+  }
+  /** Determines whether a given key is valid */
+  protected void checkKey(K key) throws InvalidKeyException {
+    try {
+      comp.compare(key,key);
+    }
+    catch(Exception e) {
+      throw new InvalidKeyException("Invalid key");
+    }
+  }
+  //end#fragment mainMethods
+  //begin#fragment auxiliary
+   /** Performs up-heap bubbling */
+  protected void upHeap(Position<Entry<K,V>> v) {
+    Position<Entry<K,V>> u;
+    while (!heap.isRoot(v)) {
+      u = heap.parent(v);
+      if (comp.compare(u.element().getKey(), v.element().getKey()) <= 0) break;
+      swap(u, v);
+      v = u;
+    }
+  }
+  /** Performs down-heap bubbling */
+  protected void downHeap(Position<Entry<K,V>> r) {
+    while (heap.isInternal(r)) {
+      Position<Entry<K,V>> s;		// the position of the smaller child
+      if (!heap.hasRight(r))
+	s = heap.left(r);
+      else if (comp.compare(heap.left(r).element().getKey(), 
+                            heap.right(r).element().getKey()) <=0)
+	s = heap.left(r);
+      else
+	s = heap.right(r);
+      if (comp.compare(s.element().getKey(), r.element().getKey()) < 0) {
+	swap(r, s);
+	r = s;
+      }
+      else 
+	break;
+    }
+  }
+  /** Swaps the entries of the two given positions */
+  protected void swap(Position<Entry<K,V>> x, Position<Entry<K,V>> y) {
+    Entry<K,V> temp = x.element();
+    heap.replace(x, y.element());
+    heap.replace(y, temp);
+  }
+  /** Text visualization for debugging purposes */
+  public String toString() {
+    return heap.toString();
+  }
+  //end#fragment auxiliary
+}