class LinkedDeque(object):
'''double-ended queue'''
def __init__(self, iterable=None):
"""Initialize this queue and enqueue the given items, if any."""
self.list = DoublyLinkedList()
self.size = 0
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={})'.format(self.length(), self.front())
def is_empty(self):
"""Return True if this queue is empty, or False otherwise."""
# runtime O(1) checking the value
if self.size == 0:
return True
else:
return False
def length(self):
"""Return the number of items in the deque"""
# runtime O(1) retrieving a variable
return self.size
def push_front(self, item):
"""Insert item at front of deque"""
# runtime O(n) having to shift all the slots in the array back
self.list.prepend(item)
self.size += 1
def push_back(self, item):
"""Insert item at back of the deque"""
# runtime O(1)*average
self.list.append(item)
self.size += 1
def front(self):
"""Returns item at front of deque"""
# runtime O(1) retrieving value at an index
return self.list.head.data
def back(self):
"""Returns item at back of the deque"""
# runtime O(1) retrieving value at an index
return self.list.tail.data
def pop_front(self):
"""Remove and return the item at the front of the deque"""
# runtime O(n) having to shift later elements up the list
self.size -= 1
return self.list.delete_index(0)
def pop_back(self):
"""Remove and return the item at the back of the deque"""
# runtime O(1) removing last element doesnt have effect on other elements
self.size -= 1
return self.list.delete_index(self.size)
def test_delete_index(self):
ll = DoublyLinkedList(['A', 'B', 'C', 'D', 'E'])
assert ll.size == 5
ll.delete_index(4)
assert ll.head.data == 'A'
assert ll.tail.data == 'D'
assert ll.size == 4
ll.delete_index(0)
assert ll.head.data == 'B'
assert ll.tail.data == 'D'
assert ll.size == 3
ll.delete_index(1)
assert ll.head.data == 'B'
assert ll.tail.data == 'D'
assert ll.size == 2
