def test_items(self):
ll = DoubleLinkedList()
assert ll.items() == []
ll.append('B')
assert ll.items() == ['B']
ll.prepend('A')
assert ll.items() == ['A', 'B']
ll.append('C')
assert ll.items() == ['A', 'B', 'C']
def test_size(self):
ll = DoubleLinkedList()
assert ll.size == 0
# append and prepend operations increment size
ll.append('B')
assert ll.size == 1
ll.prepend('A')
assert ll.size == 2
ll.append('C')
assert ll.size == 3
# delete operations decrement size
ll.delete('B')
assert ll.size == 2
ll.delete('C')
assert ll.size == 1
ll.delete('A')
assert ll.size == 0
def test_length(self):
ll = DoubleLinkedList()
assert ll.length() == 0
# append and prepend operations increase length
ll.append('B')
assert ll.head.previous == None
assert ll.head.next == None
assert ll.tail.previous == None
assert ll.tail.next == None
assert ll.length() == 1
ll.prepend('A')
assert ll.head.previous == None
assert ll.head.next.data == 'B'
assert ll.tail.previous.data == 'A'
assert ll.tail.next == None
assert ll.length() == 2
ll.append('C')
assert ll.head.previous == None
assert ll.head.next.data == 'B'
assert ll.tail.previous.data == 'B'
assert ll.tail.next == None
assert ll.length() == 3
# delete operations decrease length
ll.delete('B')
assert ll.head.previous == None
assert ll.head.next.data == 'C'
assert ll.tail.previous.data == 'A'
assert ll.tail.next == None
assert ll.length() == 2
ll.delete('C')
assert ll.head.previous == None
assert ll.head.next == None
assert ll.tail.previous == None
assert ll.tail.next == None
assert ll.length() == 1
ll.delete('A')
assert ll.head == None
assert ll.head == None
assert ll.length() == 0
def test_append(self):
ll = DoubleLinkedList()
ll.append('A')
assert ll.head.data == 'A' # new head
assert ll.tail.data == 'A' # new tail
assert ll.size == 1
ll.append('B')
assert ll.head.data == 'A' # unchanged
assert ll.tail.data == 'B' # new tail
assert ll.size == 2
assert ll.head.next.data == 'B'
assert ll.tail.previous.data == 'A'
ll.append('C')
assert ll.head.data == 'A' # unchanged
assert ll.tail.data == 'C' # new tail
assert ll.size == 3
assert ll.head.next.data == 'B'
assert ll.tail.previous.data == 'B'
class Deque(object):
def __init__(self, iterable=None):
"""Initialize this deque and enqueue the given items, if any."""
# Initialize a new linked list to store the items
self.list = DoubleLinkedList()
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.size == 0
def length(self):
"""Return the number of items in this deque."""
return self.list.size
def push_back(self, item):
"""Insert the given item at the back of this deque.
Running time: O(1)"""
# TODO: Insert given item
self.list.append(item)
def push_front(self, item):
"""Insert the given item at the front of this deque.
Running time: O(1)"""
# TODO: Insert given item
self.list.prepend(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()):
print("deque is empty!")
return None
return self.list.head.data
def back(self):
"""Return the item at the front of this deque without removing it,
or None if this deque is empty."""
if (self.is_empty()):
print("deque is empty!")
return None
return self.list.tail.data
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)"""
if (self.is_empty()):
raise ValueError("deque is empty!")
to_return = self.list.head.data
self.list.head = self.list.head.next
self.list.size -= 1
return to_return
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)"""
if (self.is_empty()):
raise ValueError("deque is empty!")
to_return = self.list.tail.data
self.list.tail = self.list.tail.previous
self.list.size -= 1
return to_return
