Python/data_structures/linked_list/circular_linked_list.py

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from typing import Any
class Node:
"""
Class to represent a single node.
Each node has following attributes
* data
* next_ptr
"""
def __init__(self, data: Any):
self.data = data
self.next_ptr = None
class CircularLinkedList:
"""
Class to represent the CircularLinkedList.
CircularLinkedList has following attributes.
* head
* length
"""
def __init__(self):
self.head = None
self.length = 0
def __len__(self) -> int:
"""
Dunder method to return length of the CircularLinkedList
>>> cll = CircularLinkedList()
>>> len(cll)
0
>>> cll.append(1)
>>> len(cll)
1
>>> cll.prepend(0)
>>> len(cll)
2
>>> cll.delete_front()
>>> len(cll)
1
>>> cll.delete_rear()
>>> len(cll)
0
"""
return self.length
def __str__(self) -> str:
"""
Dunder method to represent the string representation of the CircularLinkedList
>>> cll = CircularLinkedList()
>>> print(cll)
Empty linked list
>>> cll.append(1)
>>> cll.append(2)
>>> print(cll)
<Node data=1> => <Node data=2>
"""
current_node = self.head
if not current_node:
return "Empty linked list"
results = [current_node.data]
current_node = current_node.next_ptr
while current_node != self.head:
results.append(current_node.data)
current_node = current_node.next_ptr
return " => ".join(f"<Node data={result}>" for result in results)
def append(self, data: Any) -> None:
"""
Adds a node with given data to the end of the CircularLinkedList
>>> cll = CircularLinkedList()
>>> cll.append(1)
>>> print(f"{len(cll)}: {cll}")
1: <Node data=1>
>>> cll.append(2)
>>> print(f"{len(cll)}: {cll}")
2: <Node data=1> => <Node data=2>
"""
current_node = self.head
new_node = Node(data)
new_node.next_ptr = new_node
if current_node:
while current_node.next_ptr != self.head:
current_node = current_node.next_ptr
current_node.next_ptr = new_node
new_node.next_ptr = self.head
else:
self.head = new_node
self.length += 1
def prepend(self, data: Any) -> None:
"""
Adds a ndoe with given data to the front of the CircularLinkedList
>>> cll = CircularLinkedList()
>>> cll.prepend(1)
>>> cll.prepend(2)
>>> print(f"{len(cll)}: {cll}")
2: <Node data=2> => <Node data=1>
"""
current_node = self.head
new_node = Node(data)
new_node.next_ptr = new_node
if current_node:
while current_node.next_ptr != self.head:
current_node = current_node.next_ptr
current_node.next_ptr = new_node
new_node.next_ptr = self.head
self.head = new_node
self.length += 1
def delete_front(self) -> None:
"""
Removes the 1st node from the CircularLinkedList
>>> cll = CircularLinkedList()
>>> cll.delete_front()
Traceback (most recent call last):
...
IndexError: Deleting from an empty list
>>> cll.append(1)
>>> cll.append(2)
>>> print(f"{len(cll)}: {cll}")
2: <Node data=1> => <Node data=2>
>>> cll.delete_front()
>>> print(f"{len(cll)}: {cll}")
1: <Node data=2>
>>> cll.delete_front()
>>> print(f"{len(cll)}: {cll}")
0: Empty linked list
"""
if not self.head:
raise IndexError("Deleting from an empty list")
current_node = self.head
if current_node.next_ptr == current_node:
self.head = None
else:
while current_node.next_ptr != self.head:
current_node = current_node.next_ptr
current_node.next_ptr = self.head.next_ptr
self.head = self.head.next_ptr
self.length -= 1
if not self.head:
assert self.length == 0
def delete_rear(self) -> None:
"""
Removes the last node from the CircularLinkedList
>>> cll = CircularLinkedList()
>>> cll.delete_rear()
Traceback (most recent call last):
...
IndexError: Deleting from an empty list
>>> cll.append(1)
>>> cll.append(2)
>>> print(f"{len(cll)}: {cll}")
2: <Node data=1> => <Node data=2>
>>> cll.delete_rear()
>>> print(f"{len(cll)}: {cll}")
1: <Node data=1>
>>> cll.delete_rear()
>>> print(f"{len(cll)}: {cll}")
0: Empty linked list
"""
if not self.head:
raise IndexError("Deleting from an empty list")
temp_node, current_node = self.head, self.head
if current_node.next_ptr == current_node:
self.head = None
else:
while current_node.next_ptr != self.head:
temp_node = current_node
current_node = current_node.next_ptr
temp_node.next_ptr = current_node.next_ptr
self.length -= 1
if not self.head:
assert self.length == 0
if __name__ == "__main__":
import doctest
doctest.testmod()