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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
** $Id$
\* */
package scala.collection.mutable;
/** This class implements priority queues using a heap. The
* elements of the queue have to be ordered in terms of the
* <code>Ordered[T]</code> trait.
*
* @author Matthias Zenger
* @version 1.0, 03/05/2004
*/
//[serializable, cloneable]
class PriorityQueue[A <% Ordered[A]] extends ResizableArray[A] with java.io.Serializable {
size = size + 1; // we do not use array(0)
protected def fixUp(as: Array[A], m: Int): Unit = {
var k: Int = m;
while ((k > 1) && (as(k / 2) < as(k))) {
swap(k, k / 2);
k = k / 2;
}
}
protected def fixDown(as: Array[A], m: Int, n: Int): Unit = {
var k: Int = m;
var loop: Boolean = true;
while (loop && (n >= 2 * k)) {
var j = 2 * k;
if ((j < n) && (as(j) < as(j + 1)))
j = j + 1;
if (!(as(k) < as(j)))
loop = false;
else {
val h = as(k);
as(k) = as(j);
as(j) = h;
k = j;
}
}
}
/** Checks if the queue is empty.
*
* @return true, iff there is no element in the queue.
*/
def isEmpty: Boolean = size < 2;
/** Inserts a single element into the priority queue.
*
* @param elem the element to insert
*/
def +=(elem: A): Unit = {
ensureSize(size+1);
array(size) = elem;
fixUp(array, size);
size = size + 1;
}
/** Adds all elements provided by an <code>Iterable</code> object
* into the priority queue.
*
* @param iter an iterable object
*/
def ++=(iter: Iterable[A]): Unit = this ++= iter.elements;
/** Adds all elements provided by an iterator into the priority queue.
*
* @param it an iterator
*/
def ++=(it: Iterator[A]): Unit = it foreach { e => this += e };
/** Adds all elements to the queue.
*
* @param elems the elements to add.
*/
def enqueue(elems: A*): Unit = (this ++= elems);
/** Returns the element with the highest priority in the queue,
* and removes this element from the queue.
*
* @return the element with the highest priority.
*/
def dequeue: A = {
if (size > 1) {
size = size - 1;
swap(1, size);
fixDown(array, 1, size - 1);
array(size)
} else
error("no element to remove from heap");
}
/** Returns the element with the highest priority in the queue,
* or throws an error if there is no element contained in the queue.
*
* @return the element with the highest priority.
*/
def max: A = if (size > 1) array(1) else error("queue is empty");
/** Removes all elements from the queue. After this operation is completed,
* the queue will be empty.
*/
def clear: Unit = {
size = 1;
}
/** Returns an iterator which yiels all the elements of the priority
* queue in descending priority order.
*
* @return an iterator over all elements sorted in descending order.
*/
override def elements: Iterator[A] = new Iterator[A] {
val as: Array[A] = new Array[A](size);
java.lang.System.arraycopy(array, 0, as, 0, size);
var i = size - 1;
def hasNext: Boolean = i > 0;
def next: A = {
val res = as(1);
as(1) = as(i);
i = i - 1;
fixDown(as, 1, i);
res
}
}
/** Checks if two queues are structurally identical.
*
* @return true, iff both queues contain the same sequence of elements.
*/
override def equals(that: Any): Boolean = (
that.isInstanceOf[PriorityQueue[A]] &&
{ val other = that.asInstanceOf[PriorityQueue[A]];
elements.zip(other.elements).forall {
case Pair(thiselem, thatelem) => thiselem == thatelem;
}}
);
/** The hashCode method always yields an error, since it is not
* safe to use mutable queues as keys in hash tables.
*
* @return never.
*/
override def hashCode(): Int = error("unsuitable as hash key");
/** Returns a regular queue containing the same elements.
*/
def toQueue: Queue[A] = {
val res = new Queue[A];
res ++= this;
res
}
/** Returns a list of all elements.
*/
def toList: List[A] = elements.toList;
/** Returns a textual representation of a queue as a string.
*
* @return the string representation of this queue.
*/
override def toString() = toList.mkString("PriorityQueue(", ", ", ")");
/** This method clones the priority queue.
*
* @return a priority queue with the same elements.
*/
override def clone(): PriorityQueue[A] = {
val res = new PriorityQueue[A];
res ++= this;
res
}
}
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