MinHeap.java

/**
 * 
 */
package heaps;

import java.util.ArrayList;
import java.util.List;

/**
 * Heap tree where a node's key is higher than or equal to its parent's and lower than or equal
 * to its children's.
 * @author Nicolas Renard
 *
 */
public class MinHeap implements Heap {
 
 private final List<HeapElement> minHeap;
 
 public MinHeap(List<HeapElement> listElements) throws Exception {
 minHeap = new ArrayList<HeapElement>();
 for (HeapElement heapElement : listElements) {
 if (heapElement != null) insertElement(heapElement);
 else System.out.println("Null element. Not added to heap");
 }
 if (minHeap.size() == 0) System.out.println("No element has been added, empty heap.");
 }
 
 // Get the element at a given index. The key for the list is equal to index value - 1
 public HeapElement getElement(int elementIndex) {
 if ((elementIndex <= 0) && (elementIndex > minHeap.size())) throw new IndexOutOfBoundsException("Index out of heap range");
 return minHeap.get(elementIndex - 1);
 }
 
 // Get the key of the element at a given index
 private double getElementKey(int elementIndex) {
 return minHeap.get(elementIndex - 1).getKey();
 }
 
 // Swaps two elements in the heap
 private void swap(int index1, int index2) {
 HeapElement temporaryElement = minHeap.get(index1 - 1);
 minHeap.set(index1 - 1, minHeap.get(index2 - 1));
 minHeap.set(index2 - 1, temporaryElement);
 }
 
 // Toggle an element up to its right place as long as its key is lower than its parent's 
 private void toggleUp(int elementIndex) {
 double key = minHeap.get(elementIndex - 1).getKey();
 while (getElementKey((int) Math.floor(elementIndex/2)) > key) {
 swap(elementIndex, (int) Math.floor(elementIndex/2));
 elementIndex = (int) Math.floor(elementIndex/2);
 }
 }
 
 // Toggle an element down to its right place as long as its key is higher
 // than any of its children's 
 private void toggleDown(int elementIndex) {
 double key = minHeap.get(elementIndex - 1).getKey();
 boolean wrongOrder = (key > getElementKey(elementIndex*2)) || (key > getElementKey(Math.min(elementIndex*2, minHeap.size())));
 while ((2*elementIndex <= minHeap.size()) && wrongOrder) {
 // Check whether it shall swap the element with its left child or its right one if any.
 if ((2*elementIndex < minHeap.size()) && (getElementKey(elementIndex*2 + 1) < getElementKey(elementIndex*2))) {
 swap(elementIndex, 2*elementIndex + 1);
 elementIndex = 2*elementIndex + 1;
 }
 else {
 swap(elementIndex, 2*elementIndex);
 elementIndex = 2*elementIndex;
 }
 wrongOrder = (key > getElementKey(elementIndex*2)) || (key > getElementKey(Math.min(elementIndex*2, minHeap.size())));
 
 }
 }

 private HeapElement extractMin() {
 HeapElement result = minHeap.get(0);
 deleteElement(0);
 return result;
 }

 @Override
 public void insertElement(HeapElement element) {
 minHeap.add(element);
 toggleUp(minHeap.size());

 }

 @Override
 public void deleteElement(int elementIndex) {
		if (minHeap.isEmpty())
			try {
				throw new EmptyHeapException("Attempt to delete an element from an empty heap");
			} catch (EmptyHeapException e) {
				e.printStackTrace();
			}
 if ((elementIndex > minHeap.size()) && (elementIndex <= 0)) throw new IndexOutOfBoundsException("Index out of heap range");
 // The last element in heap replaces the one to be deleted
 minHeap.set(elementIndex - 1, getElement(minHeap.size()));
 minHeap.remove(minHeap.size());
 // Shall the new element be moved up...
 if (getElementKey(elementIndex) < getElementKey((int) Math.floor(elementIndex/2))) toggleUp(elementIndex);
 // ... or down ?
 else if (((2*elementIndex <= minHeap.size()) && (getElementKey(elementIndex) > getElementKey(elementIndex*2))) ||
 ((2*elementIndex < minHeap.size()) && (getElementKey(elementIndex) > getElementKey(elementIndex*2)))) toggleDown(elementIndex);
 }
 
 @Override
 public HeapElement getElement() throws EmptyHeapException {
 try {
 return extractMin();
 } catch (Exception e) {
 throw new EmptyHeapException("Heap is empty. Error retrieving element");
 }
 }
}