/* -*- 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/. */
/** * 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: typedeftypename 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) {}
/** * @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.
*/ void Push(T&& aElement) {
mElements.AppendElement(std::move(aElement));
// 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;
}
std::swap(mElements[i], mElements[parent]);
i = parent;
}
}
/** * 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 = std::move(mElements[0]);
// Move last to front
mElements[0] = mElements.PopLastElement();
// Sift down
size_type i = 0; while (2 * i + 1 < newLength) {
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 < newLength &&
mCompare.LessThan(mElements[r_child], mElements[swap])) {
swap = r_child;
} if (swap == i) { break;
}
std::swap(mElements[i], mElements[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(); }
nsTPriorityQueue Clone() const { auto res = nsTPriorityQueue{mCompare};
res.mElements = mElements.Clone(); return res;
}
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