def test_length(self):
ll = 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 LinkedDeque(object):
# Setting our front as the head of the doubly linked list
def __init__(self, iterable=None):
"""Initialize this deque and push_back the given items, if any."""
# Initialize a new linked list to store the items
self.list = LinkedList()
if iterable is not None:
for item in iterable:
self.push_back(item)
def __repr__(self):
"""Return a string representation of this deque."""
return 'Queue({} items, front={})'.format(self.length(), self.front())
def is_empty(self):
"""Return True if this deque is empty, or False otherwise."""
return self.list.is_empty()
def length(self):
"""Return the number of items in this deque."""
return self.list.length()
def push_front(self, item):
"""Insert the given item at the front of the linkedlist.
Running time: O(1) calling the ll prepend method by just changing the head node"""
self.list.prepend(item)
def push_back(self, item):
"""Insert the given item at the back of this deque.
Running time: O(1) calling the ll append method by just changing the tail node"""
self.list.append(item)
def front(self):
"""Return the item at the front of this deque without removing it,
or None if this deque is empty."""
if self.length() != 0:
return self.list.head.data # returning the head
else:
return None
def back(self):
"""Return the item at the end of this deque without removing it,
or None if this deque is empty."""
if self.length() != 0:
return self.list.tail.data # returning the tail
else:
return None
def pop_front(self):
"""Remove and return the item at the front of this deque,
or raise ValueError if this deque is empty.
Running time: O(1) from getting the front item and removing at the head of the ll"""
if self.length() != 0:
front_item = self.front()
self.list.delete(front_item)
return front_item
else:
raise ValueError('No items in list to pop_front: []')
def pop_back(self):
"""Remove and return the item at the back of this deque,
or raise ValueError if this deque is empty.
Running time: O(1) from getting the back item and removing at the tail of the ll"""
if self.length() != 0:
back_item = self.back()
self.list.delete(back_item)
return back_item
else:
raise ValueError('No items in list to pop_back: []')