mirror of
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162 lines
4.4 KiB
C++
162 lines
4.4 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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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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explicit 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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/**
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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 { return mElements.IsEmpty(); }
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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 { return mElements.Length(); }
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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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MOZ_ASSERT(!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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}
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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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MOZ_ASSERT(!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() { mElements.Clear(); }
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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 { return mElements.Elements(); }
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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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