def test_length(self):
ll = Doubly_LinkedList()
assert ll.length() == 0
# append and prepend operations increase length
ll.append('B')
assert ll.length() == 1
ll.prepend('A')
assert ll.length() == 2
ll.append('C')
assert ll.length() == 3
# delete operations decrease length
ll.delete('B')
assert ll.length() == 2
ll.delete('C')
assert ll.length() == 1
ll.delete('A')
assert ll.length() == 0
class Doubly_LinkedQueue(object):
def __init__(self, iterable=None):
"""Initialize this queue and enqueue the given items, if any."""
# Initialize a new linked list to store the items
self.head = None
self.tail = None
# self.size = 0
self.list = Doubly_LinkedList()
if iterable is not None:
for item in iterable:
self.enqueue(item)
def __repr__(self):
"""Return a string representation of this queue."""
return 'Queue({} items, front={})'.format(self.length(), self.front())
def is_empty(self):
"""Return True if this queue is empty, or False otherwise."""
# TODO: Check if empty
return self.list.head is None
def length(self):
"""Return the number of items in this queue."""
# TODO: Count number of items
return self.list.length()
print(self.length)
def enqueue_back(self, item):
"""Insert the given item at the back of this queue.
Running time: O(???) – Why? [TODO]"""
# TODO: Insert given item
#Append to the end of the list
self.list.append(item)
def enqueue_front(self, item):
# TODO: Insert given item
# Move the item to the start of the list
self.list.prepend(item)
def front(self):
"""Return the item at the front of this queue without removing it,
or None if this queue is empty."""
# TODO: Return front item, if any
if self.is_empty():
#raise ValueError
return None
#return self.list.head.data
self.list.pop(-1)
def back(self):
if self.is_empty():
return None
return self.list.tail.data
def dequeue_front(self):
"""Remove and return the item at the front of this queue,
or raise ValueError if this queue is empty.
Running time: O(???) – Why? [TODO]"""
# TODO: Remove and return front item, if any
#Check if head is empty
if self.is_empty():
raise ValueError
#Set the data to the tail
data = self.list.tail.data
self.list.delete(self.list.tail.data)
return data
def dequeue_back(self):
#Check if head is empty
if self.is_empty():
raise ValueError
#Set the data to the head
data = self.list.head.data
self.list.delete(self.list.head.data)
return data