1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
/* -*- 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_
|
