class QueueLinkedList(Generic[T]):
"""
Queue backed by a doubly linked list
"""
def __init__(self):
self.linked_list = DoublyLinkedList()
def __len__(self):
return self.linked_list.size()
# O(1)
def dequeue(self) -> T:
return self.linked_list.remove(0)
# O(1)
def enqueue(self, element: T):
self.linked_list.append(element)
class TestDoublyLinkedList(unittest.TestCase):
def setUp(self):
self.items = DoublyLinkedList()
# test for empty linked list
def test_empty_list(self):
self.assertEqual(self.items.head, None)
self.assertEqual(self.items.tail, None)
# Tests forbidden operations like removal in a empty linked list
def test_forbidden_operations_on_empty_linked_list(self):
self.assertEqual(self.items.size, 0)
with self.assertRaises(RuntimeError):
self.items.remove_back()
with self.assertRaises(RuntimeError):
self.items.remove_front()
def test_delete_nonexistent_item(self):
self.items.insert_back('A')
self.items.insert_front('B')
with self.assertRaises(RuntimeError):
self.items.remove('Z')
def test_insert_back(self):
self.items.insert_back('Z')
self.assertEqual(self.items.size, 1)
self.assertEqual(self.items.remove_back(), 'Z')
self.items.insert_back('Y')
self.items.insert_back('T')
self.items.insert_back('E')
self.assertEqual(self.items.remove_front(), 'Y')
def test_insert_front(self):
self.items.insert_front('A')
self.assertEqual(self.items.size, 1)
self.assertEqual(self.items.remove_front(), 'A')
self.items.insert_front('B')
self.items.insert_front('C')
self.items.insert_front('D')
self.assertEqual(self.items.remove_back(), "B")
self.assertEqual(self.items.remove_front(), "D")
def test_remove(self):
with self.assertRaises(RuntimeError):
self.items.remove('T')
self.items.insert_front('T')
self.items.insert_back('R')
self.items.insert_after('R', 'Y')
self.items.remove('R')
self.assertEqual(self.items.size, 2)
self.assertEqual(self.items.remove_back(), 'Y')
self.assertEqual(self.items.size, 1)
self.items.remove_front()
self.assertEqual(self.items.size, 0)
with self.assertRaises(RuntimeError):
self.items.remove_front()
# when only one node is there
def test_single_node_case(self):
self.items.insert_front(1)
self.items.remove_front()
self.assertEqual(self.items.head, self.items.tail)
print('Adding a few elements on the front...')
animals.insert_front('Cow')
animals.insert_front('Tiger')
animals.display()
print('\nAdding a few elements on the back...')
animals.insert_back('Lion')
animals.insert_back('Wolf')
animals.display()
print('\nAdding an item after Lion')
animals.insert_after('Lion', 'Lioness')
animals.display()
print('\nRemoving a few items from beginning..')
animals.remove_front()
animals.remove_front()
animals.display()
print('\nRemoving Lioness from the list')
animals.remove('Lioness')
animals.display()
print('\nRemoving a few items from the back')
animals.remove_back()
animals.remove_back()
animals.display()
print('\nThere are {} items on the list.'.format(animals.size))
def test_remove_empty():
doubly_linked_list = DoublyLinkedList()
assert not doubly_linked_list.remove(0)