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
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
|
// Copyright 2006 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/**
* @fileoverview Datastructure: Queue.
*
*
* This file provides the implementation of a FIFO Queue structure.
* API is similar to that of com.google.common.collect.IntQueue
*
* The implementation is a classic 2-stack queue.
* There's a "front" stack and a "back" stack.
* Items are pushed onto "back" and popped from "front".
* When "front" is empty, we replace "front" with reverse(back).
*
* Example:
* front back op
* [] [] enqueue 1
* [] [1] enqueue 2
* [] [1,2] enqueue 3
* [] [1,2,3] dequeue -> ...
* [3,2,1] [] ... -> 1
* [3,2] [] enqueue 4
* [3,2] [4] dequeue -> 2
* [3] [4]
*
* Front and back are simple javascript arrays. We rely on
* Array.push and Array.pop being O(1) amortized.
*
* Note: In V8, queues, up to a certain size, can be implemented
* just fine using Array.push and Array.shift, but other JavaScript
* engines do not have the optimization of Array.shift.
*
*/
goog.provide('goog.structs.Queue');
goog.require('goog.array');
/**
* Class for FIFO Queue data structure.
*
* @constructor
* @template T
*/
goog.structs.Queue = function() {
/**
* @private {!Array<T>} Front stack. Items are pop()'ed from here.
*/
this.front_ = [];
/**
* @private {!Array<T>} Back stack. Items are push()'ed here.
*/
this.back_ = [];
};
/**
* Flips the back stack onto the front stack if front is empty,
* to prepare for peek() or dequeue().
*
* @private
*/
goog.structs.Queue.prototype.maybeFlip_ = function() {
if (goog.array.isEmpty(this.front_)) {
this.front_ = this.back_;
this.front_.reverse();
this.back_ = [];
}
};
/**
* Puts the specified element on this queue.
* @param {T} element The element to be added to the queue.
*/
goog.structs.Queue.prototype.enqueue = function(element) {
this.back_.push(element);
};
/**
* Retrieves and removes the head of this queue.
* @return {T} The element at the head of this queue. Returns undefined if the
* queue is empty.
*/
goog.structs.Queue.prototype.dequeue = function() {
this.maybeFlip_();
return this.front_.pop();
};
/**
* Retrieves but does not remove the head of this queue.
* @return {T} The element at the head of this queue. Returns undefined if the
* queue is empty.
*/
goog.structs.Queue.prototype.peek = function() {
this.maybeFlip_();
return goog.array.peek(this.front_);
};
/**
* Returns the number of elements in this queue.
* @return {number} The number of elements in this queue.
*/
goog.structs.Queue.prototype.getCount = function() {
return this.front_.length + this.back_.length;
};
/**
* Returns true if this queue contains no elements.
* @return {boolean} true if this queue contains no elements.
*/
goog.structs.Queue.prototype.isEmpty = function() {
return goog.array.isEmpty(this.front_) && goog.array.isEmpty(this.back_);
};
/**
* Removes all elements from the queue.
*/
goog.structs.Queue.prototype.clear = function() {
this.front_ = [];
this.back_ = [];
};
/**
* Returns true if the given value is in the queue.
* @param {T} obj The value to look for.
* @return {boolean} Whether the object is in the queue.
*/
goog.structs.Queue.prototype.contains = function(obj) {
return goog.array.contains(this.front_, obj) ||
goog.array.contains(this.back_, obj);
};
/**
* Removes the first occurrence of a particular value from the queue.
* @param {T} obj Object to remove.
* @return {boolean} True if an element was removed.
*/
goog.structs.Queue.prototype.remove = function(obj) {
return goog.array.removeLast(this.front_, obj) ||
goog.array.remove(this.back_, obj);
};
/**
* Returns all the values in the queue.
* @return {!Array<T>} An array of the values in the queue.
*/
goog.structs.Queue.prototype.getValues = function() {
var res = [];
// Add the front array in reverse, then the back array.
for (var i = this.front_.length - 1; i >= 0; --i) {
res.push(this.front_[i]);
}
var len = this.back_.length;
for (var i = 0; i < len; ++i) {
res.push(this.back_[i]);
}
return res;
};
|
