class 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.list = DoublyLinkedList()
self.size = 0
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.is_empty()
def length(self):
"""Return the number of items in this queue."""
# TODO: Count number of items
return self.size
def enqueue(self, item):
"""Insert the given item at the back of this queue.
Running Time and why
O(1) every case, because we keep track of the tail at all times, and enqueue appends at the tail"""
# TODO: Insert given item
self.list.append(item) # set tail to the Node(item), constant time
self.size += 1
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():
return None
return self.list.head.data
def dequeue(self):
"""Remove and return the item at the front of this queue,
or raise ValueError if this queue is empty.
Running Time and why
O(1), because we keep track of the head at all times and dequeue removes at the head"""
# TODO: Remove and return front item, if any
if self.is_empty():
raise ValueError("Head is empty, can't dequeue")
head = self.front()
self.list.head = self.list.head.next
self.size -= 1
return head
class LinkedDeque(object):
def __init__(self, iterable=None):
self.list = DoublyLinkedList()
if iterable is not None:
for item in iterable:
self.push_back(item)
def __repr__(self):
"""Return a string representation of this deque."""
return 'Deque({} items, front={}, back={})'.format(
self.length(), self.front(), self.back())
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.size
def push_front(self, item):
"""Insert the given item at the front of this deque.
Running time: O(1) - add item front of the DoublyLinkedList"""
self.list.prepend(item)
def push_back(self, item):
"""Insert the given item at the back of this deque.
Running time: O(1) - add item back of the DoublyLinkedList"""
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.is_empty():
return None
else:
return self.list.head.data
def back(self):
"""Return the item at the back of this deque without removing it,
or None if this deque is empty."""
if self.is_empty():
return None
else:
return self.list.tail.data
def pop_front(self):
"""remove and return the item at the front of the deque.
Running time: O(1) - delete item front of the DoublyLinkedList"""
if self.is_empty():
raise ValueError('This deque is empty.')
else:
data = self.front()
self.list.head = self.list.head.next
if self.list.head is None:
self.list.tail = None
else:
self.list.head.previous = None
self.list.size -= 1
return data
def pop_back(self):
"""remove and return the item at the back of the deque.
Running time: O(1) - delete item back of the DoublyLinkedList"""
if self.is_empty():
raise ValueError('This deque is empty.')
else:
data = self.back()
self.list.tail = self.list.tail.previous
if self.list.tail is None:
self.list.head = None
else:
self.list.tail.next = None
self.list.size -= 1
return data
