-
Notifications
You must be signed in to change notification settings - Fork 4.7k
Expand file tree
/
Copy pathqueue.py
More file actions
207 lines (161 loc) · 4.95 KB
/
queue.py
File metadata and controls
207 lines (161 loc) · 4.95 KB
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
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
"""
Queue Abstract Data Type
Implementations of the queue ADT using both a fixed-size array and a
linked list. Both support enqueue, dequeue, peek, is_empty, len, and iter.
Reference: https://en.wikipedia.org/wiki/Queue_(abstract_data_type)
Complexity:
Time: O(1) for enqueue/dequeue/peek (amortized for ArrayQueue)
Space: O(n)
"""
from __future__ import annotations
from abc import ABCMeta, abstractmethod
from collections.abc import Iterator
class AbstractQueue(metaclass=ABCMeta):
"""Abstract base class for queue implementations."""
def __init__(self) -> None:
self._size = 0
def __len__(self) -> int:
return self._size
def is_empty(self) -> bool:
"""Check if the queue is empty.
Returns:
True if the queue has no elements.
"""
return self._size == 0
@abstractmethod
def enqueue(self, value: object) -> None:
pass
@abstractmethod
def dequeue(self) -> object:
pass
@abstractmethod
def peek(self) -> object:
pass
@abstractmethod
def __iter__(self) -> Iterator[object]:
pass
class ArrayQueue(AbstractQueue):
"""Queue implemented with a dynamic array.
Examples:
>>> q = ArrayQueue()
>>> q.enqueue(1)
>>> q.dequeue()
1
"""
def __init__(self, capacity: int = 10) -> None:
"""Initialize with a fixed-capacity array.
Args:
capacity: Initial capacity of the underlying array.
"""
super().__init__()
self._array: list[object | None] = [None] * capacity
self._front = 0
self._rear = 0
def __iter__(self) -> Iterator[object]:
probe = self._front
while True:
if probe == self._rear:
return
yield self._array[probe]
probe += 1
def enqueue(self, value: object) -> None:
"""Add an item to the rear of the queue.
Args:
value: The value to enqueue.
"""
if self._rear == len(self._array):
self._expand()
self._array[self._rear] = value
self._rear += 1
self._size += 1
def dequeue(self) -> object:
"""Remove and return the front item.
Returns:
The front element.
Raises:
IndexError: If the queue is empty.
"""
if self.is_empty():
raise IndexError("Queue is empty")
value = self._array[self._front]
self._array[self._front] = None
self._front += 1
self._size -= 1
return value
def peek(self) -> object:
"""Return the front element without removing it.
Returns:
The front element.
Raises:
IndexError: If the queue is empty.
"""
if self.is_empty():
raise IndexError("Queue is empty")
return self._array[self._front]
def _expand(self) -> None:
"""Double the size of the underlying array."""
self._array += [None] * len(self._array)
class QueueNode:
"""A single node in a linked-list-based queue."""
def __init__(self, value: object) -> None:
self.value = value
self.next: QueueNode | None = None
class LinkedListQueue(AbstractQueue):
"""Queue implemented with a singly linked list.
Examples:
>>> q = LinkedListQueue()
>>> q.enqueue(1)
>>> q.dequeue()
1
"""
def __init__(self) -> None:
super().__init__()
self._front: QueueNode | None = None
self._rear: QueueNode | None = None
def __iter__(self) -> Iterator[object]:
probe = self._front
while True:
if probe is None:
return
yield probe.value
probe = probe.next
def enqueue(self, value: object) -> None:
"""Add an item to the rear of the queue.
Args:
value: The value to enqueue.
"""
node = QueueNode(value)
if self._front is None:
self._front = node
self._rear = node
else:
self._rear.next = node
self._rear = node
self._size += 1
def dequeue(self) -> object:
"""Remove and return the front item.
Returns:
The front element.
Raises:
IndexError: If the queue is empty.
"""
if self.is_empty():
raise IndexError("Queue is empty")
value = self._front.value
if self._front is self._rear:
self._front = None
self._rear = None
else:
self._front = self._front.next
self._size -= 1
return value
def peek(self) -> object:
"""Return the front element without removing it.
Returns:
The front element.
Raises:
IndexError: If the queue is empty.
"""
if self.is_empty():
raise IndexError("Queue is empty")
return self._front.value