path: root/src/library/scala/collection/mutable/PriorityQueue.scala

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection
package mutable

import generic._

/** This class implements priority queues using a heap.
 *  To prioritize elements of type A there must be an implicit
 *  Ordering[A] available at creation.
 *
 *  Only the `dequeue` and `dequeueAll` methods will return methods in priority
 *  order (while removing elements from the heap).  Standard collection methods
 *  including `drop`, `iterator`, and `toString` will remove or traverse the heap
 *  in whichever order seems most convenient.
 *
 *  Therefore, printing a `PriorityQueue` will not reveal the priority order of
 *  the elements, though the highest-priority element will be printed first.  To
 *  print the elements in order, one must duplicate the `PriorityQueue` (by using
 *  `clone`, for instance) and then dequeue them:
 *
 *  @example {{{
 *  val pq = collection.mutable.PriorityQueue(1, 2, 5, 3, 7)
 *  println(pq)                  // elements probably not in order
 *  println(pq.clone.dequeueAll) // prints Vector(7, 5, 3, 2, 1)
 *  }}}
 *
 *  @tparam A    type of the elements in this priority queue.
 *  @param ord   implicit ordering used to compare the elements of type `A`.
 *
 *  @author  Matthias Zenger
 *  @version 1.0, 03/05/2004
 *  @since   1
 *
 *  @define Coll PriorityQueue
 *  @define coll priority queue
 *  @define orderDependent
 *  @define orderDependentFold
 *  @define mayNotTerminateInf
 *  @define willNotTerminateInf
 */
@deprecatedInheritance("PriorityQueue is not intended to be subclassed due to extensive private implementation details.", "2.11.0")
class PriorityQueue[A](implicit val ord: Ordering[A])
   extends AbstractIterable[A]
      with Iterable[A]
      with GenericOrderedTraversableTemplate[A, PriorityQueue]
      with IterableLike[A, PriorityQueue[A]]
      with Growable[A]
      with Builder[A, PriorityQueue[A]]
      with Serializable
      with scala.Cloneable
{
  import ord._

  private class ResizableArrayAccess[A] extends AbstractSeq[A] with ResizableArray[A] with Serializable {
    def p_size0 = size0
    def p_size0_=(s: Int) = size0 = s
    def p_array = array
    def p_ensureSize(n: Int) = super.ensureSize(n)
    def p_swap(a: Int, b: Int) = super.swap(a, b)
  }

  protected[this] override def newBuilder = new PriorityQueue[A]

  private val resarr = new ResizableArrayAccess[A]

  resarr.p_size0 += 1                  // we do not use array(0)
  def length: Int = resarr.length - 1  // adjust length accordingly
  override def size: Int = length
  override def isEmpty: Boolean = resarr.p_size0 < 2
  override def repr = this

  def result = this

  override def orderedCompanion = PriorityQueue

  private def toA(x: AnyRef): A = x.asInstanceOf[A]
  protected def fixUp(as: Array[AnyRef], m: Int): Unit = {
    var k: Int = m
    while (k > 1 && toA(as(k / 2)) < toA(as(k))) {
      resarr.p_swap(k, k / 2)
      k = k / 2
    }
  }

  protected def fixDown(as: Array[AnyRef], m: Int, n: Int): Unit = {
    var k: Int = m
    while (n >= 2 * k) {
      var j = 2 * k
      if (j < n && toA(as(j)) < toA(as(j + 1)))
        j += 1
      if (toA(as(k)) >= toA(as(j)))
        return
      else {
        val h = as(k)
        as(k) = as(j)
        as(j) = h
        k = j
      }
    }
  }

  /** Inserts a single element into the priority queue.
   *
   *  @param  elem        the element to insert.
   *  @return             this $coll.
   */
  def +=(elem: A): this.type = {
    resarr.p_ensureSize(resarr.p_size0 + 1)
    resarr.p_array(resarr.p_size0) = elem.asInstanceOf[AnyRef]
    fixUp(resarr.p_array, resarr.p_size0)
    resarr.p_size0 += 1
    this
  }

  /** Adds all elements provided by a `TraversableOnce` object
   *  into the priority queue.
   *
   *  @param  xs    a traversable object.
   *  @return       a new priority queue containing elements of both `xs` and `this`.
   */
  def ++(xs: GenTraversableOnce[A]): PriorityQueue[A] = { this.clone() ++= xs.seq }

  /** 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.
   *
   *  @throws java.util.NoSuchElementException
   *  @return   the element with the highest priority.
   */
  def dequeue(): A =
    if (resarr.p_size0 > 1) {
      resarr.p_size0 = resarr.p_size0 - 1
      resarr.p_swap(1, resarr.p_size0)
      fixDown(resarr.p_array, 1, resarr.p_size0 - 1)
      toA(resarr.p_array(resarr.p_size0))
    } else
      throw new NoSuchElementException("no element to remove from heap")

  def dequeueAll[A1 >: A, That](implicit bf: CanBuildFrom[_, A1, That]): That = {
    val b = bf.apply()
    while (nonEmpty) {
      b += dequeue()
    }
    b.result()
  }

  /** 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.
   */
  override def head: A = if (resarr.p_size0 > 1) toA(resarr.p_array(1)) else throw new NoSuchElementException("queue is empty")

  /** Removes all elements from the queue. After this operation is completed,
   *  the queue will be empty.
   */
  def clear(): Unit = { resarr.p_size0 = 1 }

  /** Returns an iterator which yields all the elements.
   *
   *  Note: The order of elements returned is undefined.
   *  If you want to traverse the elements in priority queue
   *  order, use `clone().dequeueAll.iterator`.
   *
   *  @return  an iterator over all the elements.
   */
  override def iterator: Iterator[A] = new AbstractIterator[A] {
    private var i = 1
    def hasNext: Boolean = i < resarr.p_size0
    def next(): A = {
      val n = resarr.p_array(i)
      i += 1
      toA(n)
    }
  }

  /** Returns the reverse of this queue. The priority queue that gets
   *  returned will have an inversed ordering - if for some elements
   *  `x` and `y` the original queue's ordering
   *  had `compare` returning an integer ''w'', the new one will return ''-w'',
   *  assuming the original ordering abides its contract.
   *
   *  Note that the order of the elements will be reversed unless the
   *  `compare` method returns 0. In this case, such elements
   *  will be subsequent, but their corresponding subinterval may be inappropriately
   *  reversed. However, due to the compare-equals contract, they will also be equal.
   *
   *  @return   A reversed priority queue.
   */
  def reverse = {
    val revq = new PriorityQueue[A]()(new scala.math.Ordering[A] {
      def compare(x: A, y: A) = ord.compare(y, x)
    })
    for (i <- 1 until resarr.length) revq += resarr(i)
    revq
  }

  /** Returns an iterator which yields all the elements in the reverse order
   *  than that returned by the method `iterator`.
   *
   *  Note: The order of elements returned is undefined.
   *
   *  @return  an iterator over all elements sorted in descending order.
   */
  def reverseIterator: Iterator[A] = new AbstractIterator[A] {
    private var i = resarr.p_size0 - 1
    def hasNext: Boolean = i >= 1
    def next(): A = {
      val n = resarr.p_array(i)
      i -= 1
      toA(n)
    }
  }

  /** 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 =
    throw new UnsupportedOperationException("unsuitable as hash key")

  /** Returns a regular queue containing the same elements.
   *
   *  Note: the order of elements is undefined.
   */
  def toQueue: Queue[A] = new Queue[A] ++= this.iterator

  /** Returns a textual representation of a queue as a string.
   *
   *  @return the string representation of this queue.
   */
  override def toString() = toList.mkString("PriorityQueue(", ", ", ")")

  /** Converts this $coll to a list.
   *
   *  Note: the order of elements is undefined.
   *
   *  @return a list containing all elements of this $coll.
   */
  override def toList = this.iterator.toList

  /** This method clones the priority queue.
   *
   *  @return  a priority queue with the same elements.
   */
  override def clone(): PriorityQueue[A] = new PriorityQueue[A] ++= this.iterator
}


object PriorityQueue extends OrderedTraversableFactory[PriorityQueue] {
  def newBuilder[A](implicit ord: Ordering[A]) = new PriorityQueue[A]
  implicit def canBuildFrom[A](implicit ord: Ordering[A]): CanBuildFrom[Coll, A, PriorityQueue[A]] = new GenericCanBuildFrom[A]
}