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204 строки
5.9 KiB
C++
204 строки
5.9 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is C++ priority queue implementation.
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*
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* The Initial Developer of the Original Code is Brian Birtles.
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* Portions created by the Initial Developer are Copyright (C) 2009
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Brian Birtles <birtles@gmail.com>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either of the GNU General Public License Version 2 or later (the "GPL"),
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* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#ifndef NS_TPRIORITY_QUEUE_H_
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#define NS_TPRIORITY_QUEUE_H_
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#include "nsTArray.h"
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#include "nsDebug.h"
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/**
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* A templatized priority queue data structure that uses an nsTArray to serve as
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* a binary heap. The default comparator causes this to act like a min-heap.
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* Only the LessThan method of the comparator is used.
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*/
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template<class T, class Compare = nsDefaultComparator<T, T> >
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class nsTPriorityQueue
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{
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public:
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typedef typename nsTArray<T>::size_type size_type;
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/**
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* Default constructor also creates a comparator object using the default
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* constructor for type Compare.
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*/
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nsTPriorityQueue() : mCompare(Compare()) { }
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/**
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* Constructor to allow a specific instance of a comparator object to be
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* used.
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*/
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nsTPriorityQueue(const Compare& aComp) : mCompare(aComp) { }
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/**
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* Copy constructor
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*/
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nsTPriorityQueue(const nsTPriorityQueue& aOther)
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: mElements(aOther.mElements),
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mCompare(aOther.mCompare)
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{ }
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/**
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* @return True if the queue is empty or false otherwise.
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*/
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bool IsEmpty() const
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{
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return mElements.IsEmpty();
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}
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/**
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* @return The number of elements in the queue.
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*/
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size_type Length() const
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{
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return mElements.Length();
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}
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/**
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* @return The topmost element in the queue without changing the queue. This
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* is the element 'a' such that there is no other element 'b' in the queue for
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* which Compare(b, a) returns true. (Since this container does not check
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* for duplicate entries there may exist 'b' for which Compare(a, b) returns
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* false.)
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*/
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const T& Top() const
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{
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NS_ABORT_IF_FALSE(!mElements.IsEmpty(), "Empty queue");
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return mElements[0];
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}
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/**
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* Adds an element to the queue
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* @param aElement The element to add
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* @return true on success, false on out of memory.
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*/
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bool Push(const T& aElement)
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{
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T* elem = mElements.AppendElement(aElement);
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if (!elem)
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return false; // Out of memory
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// Sift up
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size_type i = mElements.Length() - 1;
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while (i) {
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size_type parent = (size_type)((i - 1) / 2);
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if (mCompare.LessThan(mElements[parent], mElements[i])) {
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break;
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}
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Swap(i, parent);
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i = parent;
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}
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return true;
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}
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/**
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* Removes and returns the top-most element from the queue.
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* @return The topmost element, that is, the element 'a' such that there is no
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* other element 'b' in the queue for which Compare(b, a) returns true.
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* @see Top()
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*/
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T Pop()
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{
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NS_ABORT_IF_FALSE(!mElements.IsEmpty(), "Empty queue");
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T pop = mElements[0];
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// Move last to front
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mElements[0] = mElements[mElements.Length() - 1];
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mElements.TruncateLength(mElements.Length() - 1);
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// Sift down
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size_type i = 0;
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while (2*i + 1 < mElements.Length()) {
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size_type swap = i;
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size_type l_child = 2*i + 1;
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if (mCompare.LessThan(mElements[l_child], mElements[i])) {
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swap = l_child;
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}
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size_type r_child = l_child + 1;
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if (r_child < mElements.Length() &&
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mCompare.LessThan(mElements[r_child], mElements[swap])) {
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swap = r_child;
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}
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if (swap == i) {
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break;
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}
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Swap(i, swap);
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i = swap;
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}
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return pop;
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}
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/**
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* Removes all elements from the queue.
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*/
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void Clear()
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{
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mElements.Clear();
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}
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/**
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* Provides readonly access to the queue elements as an array. Generally this
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* should be avoided but may be needed in some situations such as when the
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* elements contained in the queue need to be enumerated for cycle-collection.
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* @return A pointer to the first element of the array. If the array is
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* empty, then this pointer must not be dereferenced.
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*/
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const T* Elements() const
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{
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return mElements.Elements();
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}
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protected:
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/**
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* Swaps the elements at the specified indices.
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*/
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void Swap(size_type aIndexA, size_type aIndexB)
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{
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T temp = mElements[aIndexA];
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mElements[aIndexA] = mElements[aIndexB];
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mElements[aIndexB] = temp;
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}
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nsTArray<T> mElements;
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Compare mCompare; // Comparator object
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};
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#endif // NS_TPRIORITY_QUEUE_H_
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