Python/data_structures/queue/linked_queue.py

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""" A Queue using a linked list like structure """
from __future__ import annotations
from collections.abc import Iterator
from typing import Any
class Node:
def __init__(self, data: Any) -> None:
self.data: Any = data
self.next: Node | None = None
def __str__(self) -> str:
return f"{self.data}"
class LinkedQueue:
"""
>>> queue = LinkedQueue()
>>> queue.is_empty()
True
>>> queue.put(5)
>>> queue.put(9)
>>> queue.put('python')
>>> queue.is_empty();
False
>>> queue.get()
5
>>> queue.put('algorithms')
>>> queue.get()
9
>>> queue.get()
'python'
>>> queue.get()
'algorithms'
>>> queue.is_empty()
True
>>> queue.get()
Traceback (most recent call last):
...
IndexError: dequeue from empty queue
"""
def __init__(self) -> None:
self.front: Node | None = None
self.rear: Node | None = None
def __iter__(self) -> Iterator[Any]:
node = self.front
while node:
yield node.data
node = node.next
def __len__(self) -> int:
"""
>>> queue = LinkedQueue()
>>> for i in range(1, 6):
... queue.put(i)
>>> len(queue)
5
>>> for i in range(1, 6):
... assert len(queue) == 6 - i
... _ = queue.get()
>>> len(queue)
0
"""
return len(tuple(iter(self)))
def __str__(self) -> str:
"""
>>> queue = LinkedQueue()
>>> for i in range(1, 4):
... queue.put(i)
>>> queue.put("Python")
>>> queue.put(3.14)
>>> queue.put(True)
>>> str(queue)
'1 <- 2 <- 3 <- Python <- 3.14 <- True'
"""
return " <- ".join(str(item) for item in self)
def is_empty(self) -> bool:
"""
>>> queue = LinkedQueue()
>>> queue.is_empty()
True
>>> for i in range(1, 6):
... queue.put(i)
>>> queue.is_empty()
False
"""
return len(self) == 0
def put(self, item: Any) -> None:
"""
>>> queue = LinkedQueue()
>>> queue.get()
Traceback (most recent call last):
...
IndexError: dequeue from empty queue
>>> for i in range(1, 6):
... queue.put(i)
>>> str(queue)
'1 <- 2 <- 3 <- 4 <- 5'
"""
node = Node(item)
if self.is_empty():
self.front = self.rear = node
else:
assert isinstance(self.rear, Node)
self.rear.next = node
self.rear = node
def get(self) -> Any:
"""
>>> queue = LinkedQueue()
>>> queue.get()
Traceback (most recent call last):
...
IndexError: dequeue from empty queue
>>> queue = LinkedQueue()
>>> for i in range(1, 6):
... queue.put(i)
>>> for i in range(1, 6):
... assert queue.get() == i
>>> len(queue)
0
"""
if self.is_empty():
raise IndexError("dequeue from empty queue")
assert isinstance(self.front, Node)
node = self.front
self.front = self.front.next
if self.front is None:
self.rear = None
return node.data
def clear(self) -> None:
"""
>>> queue = LinkedQueue()
>>> for i in range(1, 6):
... queue.put(i)
>>> queue.clear()
>>> len(queue)
0
>>> str(queue)
''
"""
self.front = self.rear = None
if __name__ == "__main__":
from doctest import testmod
testmod()