//----------------------------------------------------------------------------
// Heap.java               by Dale/Joyce/Weems                       Chapter 9
//
// Defines all constructs for a heap.
// The dequeue method returns the largest element in the heap.
//
// ajg-version: DWC, format, no ArrayList, no questionable casts
//----------------------------------------------------------------------------

package ch09.priorityQueues;
public class Heap<T extends Comparable<T>> implements PriQueueInterface<T> {
    private int lastIndex = -1;
    private int maxIndex;
    private T[] elements;

    public Heap(T[] elements) { // the Davis Weird Constructor DWC
	this.elements = elements;
	maxIndex = elements.length -1;
    }

    public boolean isEmpty() { return lastIndex == -1; }

    public boolean isFull()  { return lastIndex == maxIndex; }

    public void enqueue (T element) throws PriQOverflowException {
	if (lastIndex == maxIndex)
	    throw new PriQOverflowException("helpful message");
	else {
	    ++lastIndex;
	    reheapUp(element);
	}
    }

    private void reheapUp(T element) {
	int hole = lastIndex;
	while ((hole>0) && (element.compareTo(elements[parent(hole)])>0)) {
	    elements[hole] = elements[parent(hole)];
	    hole = parent(hole);
	}
	elements[hole] = element;
    }

    private int parent(int index) { return (index-1)/2; }

    public T dequeue() throws PriQUnderflowException{
	if (lastIndex == -1)
	    throw new PriQUnderflowException("Helpful msg");
	T ans    = (T)elements[0];
	T toMove = (T)elements[lastIndex--];
	if (lastIndex != -1)
	    reheapDown(toMove);
	return ans;
    }

    private void reheapDown(T element) {
	int hole = 0;
	int newhole = newHole(hole, element);
	while (newhole != hole) {
	    elements[hole] = elements[newhole];
	    hole = newhole;
	    newhole = newHole(hole, element);
	}
	elements[hole] = element;
    }

    private int newHole(int hole, T element) {
	int left  = 2 * hole + 1;
	int right = 2 * hole + 2;
	if (left > lastIndex)    // no children
	    return hole;
	if (left == lastIndex)   // one child
	    return element.compareTo(elements[left])<0 ? left : hole;
	if (elements[left].compareTo(elements[right]) <  0)
	    return element.compareTo(elements[right])<0 ? right : hole;
	return element.compareTo(elements[left])<0 ? left : hole;
    }

    public String toString() {
	String theHeap = new String("The heap is\n");
	for (int i=0; i<=lastIndex; i++)
	    theHeap += i + ".  " + elements[i] + "\n";
	return theHeap;
    }
}
// Local Variables:
// compile-command: "cd ../..; javac -Xlint:unchecked ch09/priorityQueues/Heap.java"
// End: