from typing import Any, Iterator, Optional class Node: def __init__(self, data: Any): self.data: Any = data self.next: Optional[Node] = 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 len(tuple(iter(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() assert False # This should not happen except IndexError: assert True # This should happen try: circular_linked_list.delete_tail() assert False # This should not happen except IndexError: assert True # This should happen try: circular_linked_list.delete_nth(-1) assert False except IndexError: assert True try: circular_linked_list.delete_nth(0) assert False 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()