Python/data_structures/linked_list/deque_doubly.py

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"""
Implementing Deque using DoublyLinkedList ...
Operations:
1. insertion in the front -> O(1)
2. insertion in the end -> O(1)
3. remove from the front -> O(1)
4. remove from the end -> O(1)
"""
class _DoublyLinkedBase:
""" A Private class (to be inherited) """
class _Node:
__slots__ = "_prev", "_data", "_next"
def __init__(self, link_p, element, link_n):
self._prev = link_p
self._data = element
self._next = link_n
def has_next_and_prev(self):
return " Prev -> {0}, Next -> {1}".format(
self._prev is not None, self._next is not None
)
def __init__(self):
self._header = self._Node(None, None, None)
self._trailer = self._Node(None, None, None)
self._header._next = self._trailer
self._trailer._prev = self._header
self._size = 0
def __len__(self):
return self._size
def is_empty(self):
return self.__len__() == 0
def _insert(self, predecessor, e, successor):
# Create new_node by setting it's prev.link -> header
# setting it's next.link -> trailer
new_node = self._Node(predecessor, e, successor)
predecessor._next = new_node
successor._prev = new_node
self._size += 1
return self
def _delete(self, node):
predecessor = node._prev
successor = node._next
predecessor._next = successor
successor._prev = predecessor
self._size -= 1
temp = node._data
node._prev = node._next = node._data = None
del node
return temp
class LinkedDeque(_DoublyLinkedBase):
def first(self):
"""return first element
>>> d = LinkedDeque()
>>> d.add_first('A').first()
'A'
>>> d.add_first('B').first()
'B'
"""
if self.is_empty():
raise Exception("List is empty")
return self._header._next._data
def last(self):
"""return last element
>>> d = LinkedDeque()
>>> d.add_last('A').last()
'A'
>>> d.add_last('B').last()
'B'
"""
if self.is_empty():
raise Exception("List is empty")
return self._trailer._prev._data
# DEque Insert Operations (At the front, At the end)
def add_first(self, element):
"""insertion in the front
>>> LinkedDeque().add_first('AV').first()
'AV'
"""
return self._insert(self._header, element, self._header._next)
def add_last(self, element):
"""insertion in the end
>>> LinkedDeque().add_last('B').last()
'B'
"""
return self._insert(self._trailer._prev, element, self._trailer)
# DEqueu Remove Operations (At the front, At the end)
def remove_first(self):
"""removal from the front
>>> d = LinkedDeque()
>>> d.is_empty()
True
>>> d.remove_first()
Traceback (most recent call last):
...
IndexError: remove_first from empty list
>>> d.add_first('A') # doctest: +ELLIPSIS
<linked_list.deque_doubly.LinkedDeque object at ...
>>> d.remove_first()
'A'
>>> d.is_empty()
True
"""
if self.is_empty():
raise IndexError("remove_first from empty list")
return self._delete(self._header._next)
def remove_last(self):
"""removal in the end
>>> d = LinkedDeque()
>>> d.is_empty()
True
>>> d.remove_last()
Traceback (most recent call last):
...
IndexError: remove_first from empty list
>>> d.add_first('A') # doctest: +ELLIPSIS
<linked_list.deque_doubly.LinkedDeque object at ...
>>> d.remove_last()
'A'
>>> d.is_empty()
True
"""
if self.is_empty():
raise IndexError("remove_first from empty list")
return self._delete(self._trailer._prev)