## CSci 2101: Priority Heaps

Starting code for PriorityQueueHeap:

``````
import java.util.ArrayList;
import java.util.Iterator;

/**
*
* The class implements a min-priority queue, i.e. smaller numbers have higher
* priority. For instance, if the queue contains 2, 4, 1, then 1 is returned
* first, then 2, then 4. The smallest element in the queue is called the head
* of the queue. If the queue contains several elements with the same minimal
* value, any one of them may play the role of the head.
*
* Elements inserted in the the queue must implement Comparable interface. They
* are ordered based on the ordering determined by their compareTo method.
*
* The class employs a heap-based implementation, i.e. add and remove are
* guaranteed to work in O(log(n)) time.
*
* The queue is iterable. However, there are no guarantees on the order of the
* elements, i.e. they are in general not sorted.
*
* @param <E>

*            - type of elements in the queue. Must implement Comparable<E>
*/
public class PriorityQueueHeap<E extends Comparable<E>> implements OurQueue<E>,
Iterable<E> {
private ArrayList<E> elements = new ArrayList<E>();

/**
* Returns true if this list contains no elements, false otherwise. Runs in
* constant time.
*
* @return true if this list contains no elements, false otherwise
*/
public boolean isEmpty() {
return false;
}

/**
* Returns the number of elements in this queue. Runs in constant time.
*
* @return the number of elements in this queue
*/
public int size() {
return 0;
}

/**
* Inserts the specified element at its position in the priority queue. The
* position is determined by compareTo method: the element e is placed after
* all queue elements that are smaller than e based on compareTo and before
* all elements that are >= e. Runs in at most log N time where N is the
* number of elements currently in the queue.
*
* @param e
*            - the element to be added to the queue
* @throws NullPointerException
*             - if the specified element is null
*/

}

/**
* Retrieves and removes the head of this queue. Runs in at most log N time
* where N is the number of elements currently in the queue. Throws:
* NoSuchElementException - if this queue is empty
*
* @return - the head of the queue
*/
public E remove() {
return null;
}

/**
* Retrieves but does not remove the head of this queue. Runs in constant
* time. Throws: NoSuchElementException - if this queue is empty
*
* @return - the head of the queue
*/
public E element() {
return null;
}

/**
* Removes all elements from the queue. This queue will be empty after this
* call returns.
*
* @return
*/
public void clear() {

}

/**
* Returns an iterator for the queue. There are no guarantees on the order
* of the elements, i.e. they are in general not sorted.
*/
public Iterator<E> iterator() {
return elements.iterator();
}

// swaps elements at indices i and j
// to-do: think about checking error conditions
private void swap(int i, int j) {

}

// returns the index of the parent of this node
// to-do: think about the behavior for the root
private int parent(int i) {
return 0;
}

// returns the index of the left child of this node
// to-do: think about the behavior if no such child
private int leftChild(int i) {
return 0;
}

// returns the index of the right child of this node
// to-do: think about the behavior if no such child
private int rightChild(int i) {
return 0;
}
}

``````

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