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Create priority_queue_using_list.py #2428

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Create priority_queue.py
Ashley-J-George Sep 14, 2020
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248 changes: 248 additions & 0 deletions data_structures/queue/priority_queue.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,248 @@
"""
Pure Python implementation of Priority Queue using lists
"""


class FixedPriorityQueue:
"""
In a Priority Queue the elements are entred as an when the come
But while removing or deleting an element the highest priority element is deleted in FIFO fashion
Here the lowest integer has the highest priority.
Example:
priority(0) > priority(5)
priority(16) > priority(32)
Here as an example I have taken only 3 priorities viz. 0, 1, 2
0 Being the highest priority and 2 being the lowest
You can change the priorities as per your need

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)
>>>FPQ.print_queue()
Priority 0: [10, 100, 128]
Priority 1: [70, 7, 64]
Priority 2: [1, 5, 4]
>>>print(FPQ.dequeue())
10
>>>print(FPQ.dequeue())
100
>>>print(FPQ.dequeue())
128
>>>print(FPQ.dequeue())
70
>>>print(FPQ.dequeue())
7
>>>FPQ.print_queue()
Priority 0: []
Priority 1: [64]
Priority 2: [1, 5, 4]
>>>print(FPQ.dequeue())
64
>>>print(FPQ.dequeue())
1
>>>print(FPQ.dequeue())
5
>>>print(FPQ.dequeue())
4
>>>print(FPQ.dequeue())
Traceback (most recent call last):
File "Sample.py", line 117, in <module>
print(FPQ.dequeue())
File "Sample.py", line 58, in dequeue
raise Exception("Under Flow!")
Exception: Under Flow!
"""

def __init__(self):
self.queue = [
[],
[],
[],
]

def enqueue(self, priority, data):
"""
This function enters the element into the FixedPriorityQueue based on its priority
If the priority is invalid an Exception is raised saying Invalid Priority!
If the FixedPriorityQueue is full an Exception is raised saying Over Flow!
"""
if priority > 2:
raise Exception("Invalid Priority!")
elif len(self.queue[priority]) == 100:
raise Exception("Over Flow!")
else:
self.queue[priority].append(data)

def dequeue(self):
"""
This function returns the highest priority element from the FixedPriorityQueue in FIFO fashion
If the FixedPriorityQueue is empty and this function is called then an exception is raised saying Under Flow!
"""
if (
len(self.queue[0]) == 0
and len(self.queue[1]) == 0
and len(self.queue[2]) == 0
):
raise Exception("Under Flow!")

if len(self.queue[0]) != 0:
return self.queue[0].pop(0)
elif len(self.queue[1]) != 0:
return self.queue[1].pop(0)
else:
return self.queue[2].pop(0)

def print_queue(self):
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@cclauss cclauss Sep 15, 2020 •
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Suggested change
def print_queue(self):
def __str__(self) -> str:
return "Your code goes here..."

Instead, please do def __str__(self) -> str: and then we can use str(my_queue) or print(my_queue) to see the results.

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How do you do that?

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@cclauss cclauss Sep 15, 2020 •
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Replace "Your code goes here..." with a str that you want to see.

"""
Prints each priority queue within the FixedPriorityQueue
"""
print("Priority 0:", self.queue[0])
print("Priority 1:", self.queue[1])
print("Priority 2:", self.queue[2])


class ElementPriorityQueue:
"""
Element Priority Queue is the same as Fixed Priority Queue
The only difference being the value of the element itself is the priority
The rule for priorities are the same
The lowest integer has the highest priority.
Example:
priority(0) > priority(5)
priority(16) > priority(32)
You can change the priorities as per your need

>>>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)
>>>EPQ.print_queue()
[10, 70, 100, 1, 5, 7, 4, 64, 128]
>>>print(EPQ.dequeue())
1
>>>print(EPQ.dequeue())
4
>>>print(EPQ.dequeue())
5
>>>print(EPQ.dequeue())
7
>>>print(EPQ.dequeue())
10
>>>EPQ.print_queue()
[70, 100, 64, 128]
>>>print(EPQ.dequeue())
64
>>>print(EPQ.dequeue())
70
>>>print(EPQ.dequeue())
100
>>>print(EPQ.dequeue())
128
>>>print(EPQ.dequeue())
Traceback (most recent call last):
File "Sample.py", line 132, in <module>
print(EPQ.dequeue())
File "Sample.py", line 100, in dequeue
raise Exception("Under Flow!")
Exception: Under Flow!
"""

def __init__(self):
self.queue = []

def enqueue(self, data):
"""
This function enters the element into the ElementPriorityQueue based on its value
If the ElementPriorityQueue is full an Exception is raised saying Over Flow!
"""
if len(self.queue) == 100:
raise Exception("Over Flow!")
else:
self.queue.append(data)

def dequeue(self):
"""
This function returns the highest priority element from the ElementPriorityQueue in FIFO fashion.
If the ElementPriorityQueue is empty and this function is called then an exception is raised saying Under Flow!
"""
if len(self.queue) == 0:
raise Exception("Under Flow!")
else:
data = min(self.queue)
self.queue.remove(data)
return data

def print_queue(self):
"""
Prints all the elements within the Element Priority Queue
"""
print(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)
FPQ.print_queue()
print(FPQ.dequeue())
print(FPQ.dequeue())
print(FPQ.dequeue())
print(FPQ.dequeue())
print(FPQ.dequeue())
FPQ.print_queue()
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)
EPQ.print_queue()
print(EPQ.dequeue())
print(EPQ.dequeue())
print(EPQ.dequeue())
print(EPQ.dequeue())
print(EPQ.dequeue())
EPQ.print_queue()
print(EPQ.dequeue())
print(EPQ.dequeue())
print(EPQ.dequeue())
print(EPQ.dequeue())
print(EPQ.dequeue())


if __name__ == "__main__":
fixed_priority_queue()
element_priority_queue()