Python/data_structures/linked_list/circular_linked_list.py

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from __future__ import annotations
from collections.abc import Iterator
from typing import Any
class Node:
def __init__(self, data: Any):
self.data: Any = data
self.next: Node | None = None
class CircularLinkedList:
def __init__(self):
self.head = None
self.tail = None
def __iter__(self) -> Iterator[Any]:
node = self.head
while self.head:
yield node.data
node = node.next
if node == self.head:
break
def __len__(self) -> int:
return sum(1 for _ in self)
def __repr__(self):
return "->".join(str(item) for item in iter(self))
def insert_tail(self, data: Any) -> None:
self.insert_nth(len(self), data)
def insert_head(self, data: Any) -> None:
self.insert_nth(0, data)
def insert_nth(self, index: int, data: Any) -> None:
if index < 0 or index > len(self):
raise IndexError("list index out of range.")
new_node = Node(data)
if self.head is None:
new_node.next = new_node # first node points itself
self.tail = self.head = new_node
elif index == 0: # insert at head
new_node.next = self.head
self.head = self.tail.next = new_node
else:
temp = self.head
for _ in range(index - 1):
temp = temp.next
new_node.next = temp.next
temp.next = new_node
if index == len(self) - 1: # insert at tail
self.tail = new_node
def delete_front(self):
return self.delete_nth(0)
def delete_tail(self) -> Any:
return self.delete_nth(len(self) - 1)
def delete_nth(self, index: int = 0) -> Any:
if not 0 <= index < len(self):
raise IndexError("list index out of range.")
delete_node = self.head
if self.head == self.tail: # just one node
self.head = self.tail = None
elif index == 0: # delete head node
self.tail.next = self.tail.next.next
self.head = self.head.next
else:
temp = self.head
for _ in range(index - 1):
temp = temp.next
delete_node = temp.next
temp.next = temp.next.next
if index == len(self) - 1: # delete at tail
self.tail = temp
return delete_node.data
def is_empty(self) -> bool:
return len(self) == 0
def test_circular_linked_list() -> None:
"""
>>> test_circular_linked_list()
"""
circular_linked_list = CircularLinkedList()
assert len(circular_linked_list) == 0
assert circular_linked_list.is_empty() is True
assert str(circular_linked_list) == ""
try:
circular_linked_list.delete_front()
raise AssertionError # This should not happen
except IndexError:
assert True # This should happen
try:
circular_linked_list.delete_tail()
raise AssertionError # This should not happen
except IndexError:
assert True # This should happen
try:
circular_linked_list.delete_nth(-1)
raise AssertionError
except IndexError:
assert True
try:
circular_linked_list.delete_nth(0)
raise AssertionError
except IndexError:
assert True
assert circular_linked_list.is_empty() is True
for i in range(5):
assert len(circular_linked_list) == i
circular_linked_list.insert_nth(i, i + 1)
assert str(circular_linked_list) == "->".join(str(i) for i in range(1, 6))
circular_linked_list.insert_tail(6)
assert str(circular_linked_list) == "->".join(str(i) for i in range(1, 7))
circular_linked_list.insert_head(0)
assert str(circular_linked_list) == "->".join(str(i) for i in range(0, 7))
assert circular_linked_list.delete_front() == 0
assert circular_linked_list.delete_tail() == 6
assert str(circular_linked_list) == "->".join(str(i) for i in range(1, 6))
assert circular_linked_list.delete_nth(2) == 3
circular_linked_list.insert_nth(2, 3)
assert str(circular_linked_list) == "->".join(str(i) for i in range(1, 6))
assert circular_linked_list.is_empty() is False
if __name__ == "__main__":
import doctest
doctest.testmod()