--- jsr166/src/main/java/util/PriorityQueue.java 2003/05/14 21:30:45 1.1 +++ jsr166/src/main/java/util/PriorityQueue.java 2003/05/18 18:10:02 1.2 @@ -1,64 +1,418 @@ -package java.util; + package java.util; -import java.util.*; +/* + * Todo + * + * 1) Make it serializable. + */ /** - * An unbounded (resizable) priority queue based on a priority - * heap.The take operation returns the least element with respect to - * the given ordering. (If more than one element is tied for least - * value, one of them is arbitrarily chosen to be returned -- no - * guarantees are made for ordering across ties.) Ordering follows the - * java.util.Collection conventions: Either the elements must be - * Comparable, or a Comparator must be supplied. Comparison failures - * throw ClassCastExceptions during insertions and extractions. - **/ -public class PriorityQueue extends AbstractCollection implements Queue { - public PriorityQueue(int initialCapacity) {} - public PriorityQueue(int initialCapacity, Comparator comparator) {} + * An unbounded priority queue based on a priority heap. This queue orders + * elements according to the order specified at creation time. This order is + * specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered + * either according to their natural order (see {@link Comparable}), or + * according to a {@link Comparator}, depending on which constructor is used. + * The {@link #peek}, {@link #poll}, and {@link #remove} methods return the + * minimal element with respect to the specified ordering. If multiple + * these elements are tied for least value, no guarantees are made as to + * which of elements is returned. + * + *

Each priority queue has a capacity. The capacity is the size of + * the array used to store the elements on the queue. It is always at least + * as large as the queue size. As elements are added to a priority list, + * its capacity grows automatically. The details of the growth policy are not + * specified. + * + *

Implementation note: this implementation provides O(log(n)) time for + * the offer, poll, remove() and add + * methods; linear time for the remove(Object) and + * contains methods; and constant time for the peek, + * element, and size methods. + * + *

This class is a member of the + * + * Java Collections Framework. + */ +public class PriorityQueue extends AbstractQueue + implements Queue +{ + private static final int DEFAULT_INITIAL_CAPACITY = 11; - public PriorityQueue(int initialCapacity, Collection initialElements) {} + /** + * Priority queue represented as a balanced binary heap: the two children + * of queue[n] are queue[2*n] and queue[2*n + 1]. The priority queue is + * ordered by comparator, or by the elements' natural ordering, if + * comparator is null: For each node n in the heap, and each descendant + * of n, d, n <= d. + * + * The element with the lowest value is in queue[1] (assuming the queue is + * nonempty). A one-based array is used in preference to the traditional + * zero-based array to simplify parent and child calculations. + * + * queue.length must be >= 2, even if size == 0. + */ + private E[] queue; - public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {} + /** + * The number of elements in the priority queue. + */ + private int size = 0; - public boolean add(E x) { - return false; - } - public boolean offer(E x) { - return false; - } - public boolean remove(Object x) { - return false; + /** + * The comparator, or null if priority queue uses elements' + * natural ordering. + */ + private final Comparator comparator; + + /** + * The number of times this priority queue has been + * structurally modified. See AbstractList for gory details. + */ + private int modCount = 0; + + /** + * Create a new priority queue with the default initial capacity (11) + * that orders its elements according to their natural ordering. + */ + public PriorityQueue() { + this(DEFAULT_INITIAL_CAPACITY); } - public E remove() { - return null; + /** + * Create a new priority queue with the specified initial capacity + * that orders its elements according to their natural ordering. + * + * @param initialCapacity the initial capacity for this priority queue. + */ + public PriorityQueue(int initialCapacity) { + this(initialCapacity, null); } - public Iterator iterator() { - return null; + + /** + * Create a new priority queue with the specified initial capacity (11) + * that orders its elements according to the specified comparator. + * + * @param initialCapacity the initial capacity for this priority queue. + * @param comparator the comparator used to order this priority queue. + */ + public PriorityQueue(int initialCapacity, Comparator comparator) { + if (initialCapacity < 1) + initialCapacity = 1; + queue = new E[initialCapacity + 1]; + this.comparator = comparator; } - public E element() { - return null; + /** + * Create a new priority queue containing the elements in the specified + * collection. The priority queue has an initial capacity of 110% of the + * size of the specified collection. If the specified collection + * implements the {@link Sorted} interface, the priority queue will be + * sorted according to the same comparator, or according to its elements' + * natural order if the collection is sorted according to its elements' + * natural order. If the specified collection does not implement the + * Sorted interface, the priority queue is ordered according to + * its elements' natural order. + * + * @param initialElements the collection whose elements are to be placed + * into this priority queue. + * @throws ClassCastException if elements of the specified collection + * cannot be compared to one another according to the priority + * queue's ordering. + * @throws NullPointerException if the specified collection or an + * element of the specified collection is null. + */ + public PriorityQueue(Collection initialElements) { + int sz = initialElements.size(); + int initialCapacity = (int)Math.min((sz * 110L) / 100, + Integer.MAX_VALUE - 1); + if (initialCapacity < 1) + initialCapacity = 1; + queue = new E[initialCapacity + 1]; + + /* Commented out to compile with generics compiler + + if (initialElements instanceof Sorted) { + comparator = ((Sorted)initialElements).comparator(); + for (Iterator i = initialElements.iterator(); i.hasNext(); ) + queue[++size] = i.next(); + } else { + */ + { + comparator = null; + for (Iterator i = initialElements.iterator(); i.hasNext(); ) + add(i.next()); + } } + + // Queue Methods + + /** + * Remove and return the minimal element from this priority queue if + * it contains one or more elements, otherwise null. The term + * minimal is defined according to this priority queue's order. + * + * @return the minimal element from this priority queue if it contains + * one or more elements, otherwise null. + */ public E poll() { - return null; + if (size == 0) + return null; + return remove(1); } + + /** + * Return, but do not remove, the minimal element from the priority queue, + * or null if the queue is empty. The term minimal is + * defined according to this priority queue's order. This method returns + * the same object reference that would be returned by by the + * poll method. The two methods differ in that this method + * does not remove the element from the priority queue. + * + * @return the minimal element from this priority queue if it contains + * one or more elements, otherwise null. + */ public E peek() { - return null; + return queue[1]; } - public boolean isEmpty() { + // Collection Methods + + /** + * Removes a single instance of the specified element from this priority + * queue, if it is present. Returns true if this collection contained the + * specified element (or equivalently, if this collection changed as a + * result of the call). + * + * @param o element to be removed from this collection, if present. + * @return true if this collection changed as a result of the + * call + * @throws ClassCastException if the specified element cannot be compared + * with elements currently in the priority queue according + * to the priority queue's ordering. + * @throws NullPointerException if the specified element is null. + */ + public boolean remove(Object element) { + if (element == null) + throw new NullPointerException(); + + if (comparator == null) { + for (int i = 1; i <= size; i++) { + if (((Comparable)queue[i]).compareTo(element) == 0) { + remove(i); + return true; + } + } + } else { + for (int i = 1; i <= size; i++) { + if (comparator.compare(queue[i], (E) element) == 0) { + remove(i); + return true; + } + } + } return false; } + + /** + * Returns an iterator over the elements in this priority queue. The + * first element returned by this iterator is the same element that + * would be returned by a call to peek. + * + * @return an Iterator over the elements in this priority queue. + */ + public Iterator iterator() { + return new Itr(); + } + + private class Itr implements Iterator { + /** + * Index (into queue array) of element to be returned by + * subsequent call to next. + */ + int cursor = 1; + + /** + * Index of element returned by most recent call to next or + * previous. Reset to 0 if this element is deleted by a call + * to remove. + */ + int lastRet = 0; + + /** + * The modCount value that the iterator believes that the backing + * List should have. If this expectation is violated, the iterator + * has detected concurrent modification. + */ + int expectedModCount = modCount; + + public boolean hasNext() { + return cursor <= size; + } + + public E next() { + checkForComodification(); + if (cursor > size) + throw new NoSuchElementException(); + E result = queue[cursor]; + lastRet = cursor++; + return result; + } + + public void remove() { + if (lastRet == 0) + throw new IllegalStateException(); + checkForComodification(); + + PriorityQueue.this.remove(lastRet); + if (lastRet < cursor) + cursor--; + lastRet = 0; + expectedModCount = modCount; + } + + final void checkForComodification() { + if (modCount != expectedModCount) + throw new ConcurrentModificationException(); + } + } + + /** + * Returns the number of elements in this priority queue. + * + * @return the number of elements in this priority queue. + */ public int size() { - return 0; + return size; } - public Object[] toArray() { - return null; + + /** + * Add the specified element to this priority queue. + * + * @param element the element to add. + * @return true + * @throws ClassCastException if the specified element cannot be compared + * with elements currently in the priority queue according + * to the priority queue's ordering. + * @throws NullPointerException if the specified element is null. + */ + public boolean offer(E element) { + if (element == null) + throw new NullPointerException(); + modCount++; + + // Grow backing store if necessary + if (++size == queue.length) { + E[] newQueue = new E[2 * queue.length]; + System.arraycopy(queue, 0, newQueue, 0, size); + queue = newQueue; + } + + queue[size] = element; + fixUp(size); + return true; } - public T[] toArray(T[] array) { - return null; + /** + * Remove all elements from the priority queue. + */ + public void clear() { + modCount++; + + // Null out element references to prevent memory leak + for (int i=1; i<=size; i++) + queue[i] = null; + + size = 0; + } + + /** + * Removes and returns the ith element from queue. Recall + * that queue is one-based, so 1 <= i <= size. + * + * XXX: Could further special-case i==size, but is it worth it? + * XXX: Could special-case i==0, but is it worth it? + */ + private E remove(int i) { + assert i <= size; + modCount++; + + E result = queue[i]; + queue[i] = queue[size]; + queue[size--] = null; // Drop extra ref to prevent memory leak + if (i <= size) + fixDown(i); + return result; } + /** + * Establishes the heap invariant (described above) assuming the heap + * satisfies the invariant except possibly for the leaf-node indexed by k + * (which may have a nextExecutionTime less than its parent's). + * + * This method functions by "promoting" queue[k] up the hierarchy + * (by swapping it with its parent) repeatedly until queue[k] + * is greater than or equal to its parent. + */ + private void fixUp(int k) { + if (comparator == null) { + while (k > 1) { + int j = k >> 1; + if (((Comparable)queue[j]).compareTo(queue[k]) <= 0) + break; + E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } else { + while (k > 1) { + int j = k >> 1; + if (comparator.compare(queue[j], queue[k]) <= 0) + break; + E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } + } + + /** + * Establishes the heap invariant (described above) in the subtree + * rooted at k, which is assumed to satisfy the heap invariant except + * possibly for node k itself (which may be greater than its children). + * + * This method functions by "demoting" queue[k] down the hierarchy + * (by swapping it with its smaller child) repeatedly until queue[k] + * is less than or equal to its children. + */ + private void fixDown(int k) { + int j; + if (comparator == null) { + while ((j = k << 1) <= size) { + if (j 0) + j++; // j indexes smallest kid + if (((Comparable)queue[k]).compareTo(queue[j]) <= 0) + break; + E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } else { + while ((j = k << 1) <= size) { + if (j < size && comparator.compare(queue[j], queue[j+1]) > 0) + j++; // j indexes smallest kid + if (comparator.compare(queue[k], queue[j]) <= 0) + break; + E tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp; + k = j; + } + } + } + + /** + * Returns the comparator associated with this priority queue, or + * null if it uses its elements' natural ordering. + * + * @return the comparator associated with this priority queue, or + * null if it uses its elements' natural ordering. + */ + Comparator comparator() { + return comparator; + } }