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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef NS_TPRIORITY_QUEUE_H_
+#define NS_TPRIORITY_QUEUE_H_
+
+#include "nsTArray.h"
+#include "nsDebug.h"
+
+/**
+ * A templatized priority queue data structure that uses an nsTArray to serve as
+ * a binary heap. The default comparator causes this to act like a min-heap.
+ * Only the LessThan method of the comparator is used.
+ */
+template<class T, class Compare = nsDefaultComparator<T, T>>
+class nsTPriorityQueue
+{
+public:
+ typedef typename nsTArray<T>::size_type size_type;
+
+ /**
+ * Default constructor also creates a comparator object using the default
+ * constructor for type Compare.
+ */
+ nsTPriorityQueue() : mCompare(Compare()) {}
+
+ /**
+ * Constructor to allow a specific instance of a comparator object to be
+ * used.
+ */
+ explicit nsTPriorityQueue(const Compare& aComp) : mCompare(aComp) {}
+
+ /**
+ * Copy constructor
+ */
+ nsTPriorityQueue(const nsTPriorityQueue& aOther)
+ : mElements(aOther.mElements)
+ , mCompare(aOther.mCompare)
+ {
+ }
+
+ /**
+ * @return True if the queue is empty or false otherwise.
+ */
+ bool IsEmpty() const { return mElements.IsEmpty(); }
+
+ /**
+ * @return The number of elements in the queue.
+ */
+ size_type Length() const { return mElements.Length(); }
+
+ /**
+ * @return The topmost element in the queue without changing the queue. This
+ * is the element 'a' such that there is no other element 'b' in the queue for
+ * which Compare(b, a) returns true. (Since this container does not check
+ * for duplicate entries there may exist 'b' for which Compare(a, b) returns
+ * false.)
+ */
+ const T& Top() const
+ {
+ MOZ_ASSERT(!mElements.IsEmpty(), "Empty queue");
+ return mElements[0];
+ }
+
+ /**
+ * Adds an element to the queue
+ * @param aElement The element to add
+ * @return true on success, false on out of memory.
+ */
+ bool Push(const T& aElement)
+ {
+ T* elem = mElements.AppendElement(aElement);
+ if (!elem) {
+ return false; // Out of memory
+ }
+
+ // Sift up
+ size_type i = mElements.Length() - 1;
+ while (i) {
+ size_type parent = (size_type)((i - 1) / 2);
+ if (mCompare.LessThan(mElements[parent], mElements[i])) {
+ break;
+ }
+ Swap(i, parent);
+ i = parent;
+ }
+
+ return true;
+ }
+
+ /**
+ * Removes and returns the top-most element from the queue.
+ * @return The topmost element, that is, the element 'a' such that there is no
+ * other element 'b' in the queue for which Compare(b, a) returns true.
+ * @see Top()
+ */
+ T Pop()
+ {
+ MOZ_ASSERT(!mElements.IsEmpty(), "Empty queue");
+ T pop = mElements[0];
+
+ // Move last to front
+ mElements[0] = mElements[mElements.Length() - 1];
+ mElements.TruncateLength(mElements.Length() - 1);
+
+ // Sift down
+ size_type i = 0;
+ while (2 * i + 1 < mElements.Length()) {
+ size_type swap = i;
+ size_type l_child = 2 * i + 1;
+ if (mCompare.LessThan(mElements[l_child], mElements[i])) {
+ swap = l_child;
+ }
+ size_type r_child = l_child + 1;
+ if (r_child < mElements.Length() &&
+ mCompare.LessThan(mElements[r_child], mElements[swap])) {
+ swap = r_child;
+ }
+ if (swap == i) {
+ break;
+ }
+ Swap(i, swap);
+ i = swap;
+ }
+
+ return pop;
+ }
+
+ /**
+ * Removes all elements from the queue.
+ */
+ void Clear() { mElements.Clear(); }
+
+ /**
+ * Provides readonly access to the queue elements as an array. Generally this
+ * should be avoided but may be needed in some situations such as when the
+ * elements contained in the queue need to be enumerated for cycle-collection.
+ * @return A pointer to the first element of the array. If the array is
+ * empty, then this pointer must not be dereferenced.
+ */
+ const T* Elements() const { return mElements.Elements(); }
+
+protected:
+ /**
+ * Swaps the elements at the specified indices.
+ */
+ void Swap(size_type aIndexA, size_type aIndexB)
+ {
+ T temp = mElements[aIndexA];
+ mElements[aIndexA] = mElements[aIndexB];
+ mElements[aIndexB] = temp;
+ }
+
+ nsTArray<T> mElements;
+ Compare mCompare; // Comparator object
+};
+
+#endif // NS_TPRIORITY_QUEUE_H_