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70368a757e
* CircularQueueLinkedList: empty list, trivial implementation TheAlgorithms#5361 * CircularQueueLinkedList: single element list TheAlgorithms#5361 * CircularQueueLinkedList: refactor, no que empty attribute TheAlgorithms#5361 * CircularQueueLinkedList: refactor TheAlgorithms#5361 * CircularQueueLinkedList: changed internal data structure to use double linked list TheAlgorithms#5361 * CircularQueueLinkedList: enqueue test cases added TheAlgorithms#5361 * CircularQueueLinkedList: track full queue TheAlgorithms#5361 * CircularQueueLinkedList: adding functions description TheAlgorithms#5361 * CircularQueueLinkedList: type hints TheAlgorithms#5361 * CircularQueueLinkedList: algorithm explanation TheAlgorithms#5361 * CircularQueueLinkedList: missing type hints TheAlgorithms#5361 * CircularQueueLinkedList: more missing type hints TheAlgorithms#5361 * Update data_structures/queue/circular_queue_linked_list.py Co-authored-by: John Law <johnlaw.po@gmail.com>
151 lines
3.8 KiB
Python
151 lines
3.8 KiB
Python
# Implementation of Circular Queue using linked lists
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# https://en.wikipedia.org/wiki/Circular_buffer
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from typing import Any
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class CircularQueueLinkedList:
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"""
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Circular FIFO list with the given capacity (default queue length : 6)
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>>> cq = CircularQueueLinkedList(2)
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>>> cq.enqueue('a')
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>>> cq.enqueue('b')
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>>> cq.enqueue('c')
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Traceback (most recent call last):
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...
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Exception: Full Queue
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"""
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def __init__(self, initial_capacity: int = 6) -> None:
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self.front = None
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self.rear = None
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self.create_linked_list(initial_capacity)
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def create_linked_list(self, initial_capacity: int) -> None:
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current_node = Node()
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self.front = current_node
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self.rear = current_node
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previous_node = current_node
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for i in range(1, initial_capacity):
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current_node = Node()
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previous_node.next = current_node
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current_node.prev = previous_node
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previous_node = current_node
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previous_node.next = self.front
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self.front.prev = previous_node
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def is_empty(self) -> bool:
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"""
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Checks where the queue is empty or not
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>>> cq = CircularQueueLinkedList()
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>>> cq.is_empty()
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True
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>>> cq.enqueue('a')
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>>> cq.is_empty()
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False
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>>> cq.dequeue()
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'a'
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>>> cq.is_empty()
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True
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"""
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return self.front == self.rear and self.front.data is None
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def first(self) -> Any:
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"""
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Returns the first element of the queue
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>>> cq = CircularQueueLinkedList()
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>>> cq.first()
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Traceback (most recent call last):
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...
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Exception: Empty Queue
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>>> cq.enqueue('a')
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>>> cq.first()
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'a'
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>>> cq.dequeue()
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'a'
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>>> cq.first()
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Traceback (most recent call last):
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...
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Exception: Empty Queue
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>>> cq.enqueue('b')
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>>> cq.enqueue('c')
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>>> cq.first()
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'b'
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"""
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self.check_can_perform_operation()
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return self.front.data
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def enqueue(self, data: Any) -> None:
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"""
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Saves data at the end of the queue
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>>> cq = CircularQueueLinkedList()
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>>> cq.enqueue('a')
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>>> cq.enqueue('b')
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>>> cq.dequeue()
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'a'
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>>> cq.dequeue()
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'b'
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>>> cq.dequeue()
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Traceback (most recent call last):
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...
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Exception: Empty Queue
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"""
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self.check_is_full()
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if self.is_empty():
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self.rear.data = data
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else:
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self.rear = self.rear.next
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self.rear.data = data
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def dequeue(self) -> Any:
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"""
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Removes and retrieves the first element of the queue
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>>> cq = CircularQueueLinkedList()
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>>> cq.dequeue()
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Traceback (most recent call last):
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...
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Exception: Empty Queue
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>>> cq.enqueue('a')
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>>> cq.dequeue()
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'a'
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>>> cq.dequeue()
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Traceback (most recent call last):
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...
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Exception: Empty Queue
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"""
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self.check_can_perform_operation()
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if self.front == self.rear:
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data = self.front.data
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self.front.data = None
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return data
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old_front = self.front
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self.front = old_front.next
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data = old_front.data
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old_front.data = None
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return data
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def check_can_perform_operation(self) -> None:
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if self.is_empty():
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raise Exception("Empty Queue")
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def check_is_full(self) -> None:
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if self.rear.next == self.front:
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raise Exception("Full Queue")
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class Node:
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def __init__(self) -> None:
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self.data = None
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self.next = None
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self.prev = None
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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