FilesExpand file tree

master

/

priority_queue_using_list.py

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

232 lines (208 loc) · 5.56 KB

master

/

priority_queue_using_list.py

Copy path

Top

File metadata and controls

• Code
• Blame

232 lines (208 loc) · 5.56 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

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

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

"""

Pure Python implementations of a Fixed Priority Queue and an Element Priority Queue

using Python lists.

"""

class OverFlowError(Exception):

pass

class UnderFlowError(Exception):

pass

class FixedPriorityQueue:

"""

Tasks can be added to a Priority Queue at any time and in any order but when Tasks

are removed then the Task with the highest priority is removed in FIFO order. In

code we will use three levels of priority with priority zero Tasks being the most

urgent (high priority) and priority 2 tasks being the least urgent.

Examples

>>> fpq = FixedPriorityQueue()

>>> fpq.enqueue(0, 10)

>>> fpq.enqueue(1, 70)

>>> fpq.enqueue(0, 100)

>>> fpq.enqueue(2, 1)

>>> fpq.enqueue(2, 5)

>>> fpq.enqueue(1, 7)

>>> fpq.enqueue(2, 4)

>>> fpq.enqueue(1, 64)

>>> fpq.enqueue(0, 128)

>>> print(fpq)

Priority 0: [10, 100, 128]

Priority 1: [70, 7, 64]

Priority 2: [1, 5, 4]

>>> fpq.dequeue()

10

>>> fpq.dequeue()

100

>>> fpq.dequeue()

128

>>> fpq.dequeue()

70

>>> fpq.dequeue()

7

>>> print(fpq)

Priority 0: []

Priority 1: [64]

Priority 2: [1, 5, 4]

>>> fpq.dequeue()

64

>>> fpq.dequeue()

1

>>> fpq.dequeue()

5

>>> fpq.dequeue()

4

>>> fpq.dequeue()

Traceback (most recent call last):

...

data_structures.queue.priority_queue_using_list.UnderFlowError: All queues are empty

>>> print(fpq)

Priority 0: []

Priority 1: []

Priority 2: []

"""

def __init__(self):

self.queues = [

[],

[],

[],

]

def enqueue(self, priority: int, data: int) -> None:

"""

Add an element to a queue based on its priority.

If the priority is invalid ValueError is raised.

If the queue is full an OverFlowError is raised.

"""

try:

if len(self.queues[priority]) >= 100:

raise OverflowError("Maximum queue size is 100")

self.queues[priority].append(data)

except IndexError:

raise ValueError("Valid priorities are 0, 1, and 2")

def dequeue(self) -> int:

"""

Return the highest priority element in FIFO order.

If the queue is empty then an under flow exception is raised.

"""

for queue in self.queues:

if queue:

return queue.pop(0)

raise UnderFlowError("All queues are empty")

def __str__(self) -> str:

return "\n".join(f"Priority {i}: {q}" for i, q in enumerate(self.queues))

class ElementPriorityQueue:

"""

Element Priority Queue is the same as Fixed Priority Queue except that the value of

the element itself is the priority. The rules for priorities are the same the as

Fixed Priority Queue.

>>> epq = ElementPriorityQueue()

>>> epq.enqueue(10)

>>> epq.enqueue(70)

>>> epq.enqueue(4)

>>> epq.enqueue(1)

>>> epq.enqueue(5)

>>> epq.enqueue(7)

>>> epq.enqueue(4)

>>> epq.enqueue(64)

>>> epq.enqueue(128)

>>> print(epq)

[10, 70, 4, 1, 5, 7, 4, 64, 128]

>>> epq.dequeue()

1

>>> epq.dequeue()

4

>>> epq.dequeue()

4

>>> epq.dequeue()

5

>>> epq.dequeue()

7

>>> epq.dequeue()

10

>>> print(epq)

[70, 64, 128]

>>> epq.dequeue()

64

>>> epq.dequeue()

70

>>> epq.dequeue()

128

>>> epq.dequeue()

Traceback (most recent call last):

...

data_structures.queue.priority_queue_using_list.UnderFlowError: The queue is empty

>>> print(epq)

[]

"""

def __init__(self):

self.queue = []

def enqueue(self, data: int) -> None:

"""

This function enters the element into the queue

If the queue is full an Exception is raised saying Over Flow!

"""

if len(self.queue) == 100:

raise OverFlowError("Maximum queue size is 100")

self.queue.append(data)

def dequeue(self) -> int:

"""

Return the highest priority element in FIFO order.

If the queue is empty then an under flow exception is raised.

"""

if not self.queue:

raise UnderFlowError("The queue is empty")

else:

data = min(self.queue)

self.queue.remove(data)

return data

def __str__(self) -> str:

"""

Prints all the elements within the Element Priority Queue

"""

return str(self.queue)

def fixed_priority_queue():

fpq = FixedPriorityQueue()

fpq.enqueue(0, 10)

fpq.enqueue(1, 70)

fpq.enqueue(0, 100)

fpq.enqueue(2, 1)

fpq.enqueue(2, 5)

fpq.enqueue(1, 7)

fpq.enqueue(2, 4)

fpq.enqueue(1, 64)

fpq.enqueue(0, 128)

print(fpq)

print(fpq.dequeue())

print(fpq.dequeue())

print(fpq.dequeue())

print(fpq.dequeue())

print(fpq.dequeue())

print(fpq)

print(fpq.dequeue())

print(fpq.dequeue())

print(fpq.dequeue())

print(fpq.dequeue())

print(fpq.dequeue())

def element_priority_queue():

epq = ElementPriorityQueue()

epq.enqueue(10)

epq.enqueue(70)

epq.enqueue(100)

epq.enqueue(1)

epq.enqueue(5)

epq.enqueue(7)

epq.enqueue(4)

epq.enqueue(64)

epq.enqueue(128)

print(epq)

print(epq.dequeue())

print(epq.dequeue())

print(epq.dequeue())

print(epq.dequeue())

print(epq.dequeue())

print(epq)

print(epq.dequeue())

print(epq.dequeue())

print(epq.dequeue())

print(epq.dequeue())

print(epq.dequeue())

if __name__ == "__main__":

fixed_priority_queue()

element_priority_queue()