Python/data_structures/queue/circular_queue_linked_list.py at master · imanghotbi-python/Python · GitHub

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# Implementation of Circular Queue using linked lists
# https://en.wikipedia.org/wiki/Circular_buffer

from __future__ importannotations

fromtypingimportAny


classCircularQueueLinkedList:
"""
 Circular FIFO list with the given capacity (default queue length : 6)

 >>> cq = CircularQueueLinkedList(2)
 >>> cq.enqueue('a')
 >>> cq.enqueue('b')
 >>> cq.enqueue('c')
 Traceback (most recent call last):
 ...
 Exception: Full Queue
 """

def__init__(self, initial_capacity: int=6) ->None:
self.front: Node|None=None
self.rear: Node|None=None
self.create_linked_list(initial_capacity)

defcreate_linked_list(self, initial_capacity: int) ->None:
current_node=Node()
self.front=current_node
self.rear=current_node
previous_node=current_node
for_inrange(1, initial_capacity):
current_node=Node()
previous_node.next=current_node
current_node.prev=previous_node
previous_node=current_node
previous_node.next=self.front
self.front.prev=previous_node

defis_empty(self) ->bool:
"""
 Checks where the queue is empty or not
 >>> cq = CircularQueueLinkedList()
 >>> cq.is_empty()
 True
 >>> cq.enqueue('a')
 >>> cq.is_empty()
 False
 >>> cq.dequeue()
 'a'
 >>> cq.is_empty()
 True
 """

return (
self.front==self.rear
andself.frontisnotNone
andself.front.dataisNone
 )

deffirst(self) ->Any|None:
"""
 Returns the first element of the queue
 >>> cq = CircularQueueLinkedList()
 >>> cq.first()
 Traceback (most recent call last):
 ...
 Exception: Empty Queue
 >>> cq.enqueue('a')
 >>> cq.first()
 'a'
 >>> cq.dequeue()
 'a'
 >>> cq.first()
 Traceback (most recent call last):
 ...
 Exception: Empty Queue
 >>> cq.enqueue('b')
 >>> cq.enqueue('c')
 >>> cq.first()
 'b'
 """
self.check_can_perform_operation()
returnself.front.dataifself.frontelseNone

defenqueue(self, data: Any) ->None:
"""
 Saves data at the end of the queue

 >>> cq = CircularQueueLinkedList()
 >>> cq.enqueue('a')
 >>> cq.enqueue('b')
 >>> cq.dequeue()
 'a'
 >>> cq.dequeue()
 'b'
 >>> cq.dequeue()
 Traceback (most recent call last):
 ...
 Exception: Empty Queue
 """
ifself.rearisNone:
return

self.check_is_full()
ifnotself.is_empty():
self.rear=self.rear.next
ifself.rear:
self.rear.data=data

defdequeue(self) ->Any:
"""
 Removes and retrieves the first element of the queue

 >>> cq = CircularQueueLinkedList()
 >>> cq.dequeue()
 Traceback (most recent call last):
 ...
 Exception: Empty Queue
 >>> cq.enqueue('a')
 >>> cq.dequeue()
 'a'
 >>> cq.dequeue()
 Traceback (most recent call last):
 ...
 Exception: Empty Queue
 """
self.check_can_perform_operation()
ifself.rearisNoneorself.frontisNone:
return
ifself.front==self.rear:
data=self.front.data
self.front.data=None
returndata

old_front=self.front
self.front=old_front.next
data=old_front.data
old_front.data=None
returndata

defcheck_can_perform_operation(self) ->None:
ifself.is_empty():
raiseException("Empty Queue")

defcheck_is_full(self) ->None:
ifself.rearandself.rear.next==self.front:
raiseException("Full Queue")


classNode:
def__init__(self) ->None:
self.data: Any|None=None
self.next: Node|None=None
self.prev: Node|None=None


if__name__=="__main__":
importdoctest

doctest.testmod()