def __init__(self):
""" Creates an empty cursor-based list."""
self._header = Node2Way(None)
self._trailer = Node2Way(None)
self._trailer.setPrevious(self._header)
self._header.setNext(self._trailer)
self._current = None
self._size = 0
def insertBefore(self, item):
"""Inserts item before the current item, or
as the only item if the list is empty. The new item is the
current item."""
if self.isEmpty():
self._current = Node2Way(item)
self._header.setNext(self._current)
self._trailer.setPrevious(self._current)
self._current.setNext(self._trailer)
self._current.setPrevious(self._header)
else:
new = Node2Way(item)
new.setNext(self._current)
new.setPrevious(self._current.getPrevious())
self._current.getPrevious().setNext(new)
self._current.setPrevious(new)
self._current = new
self._size += 1
def replace(self, newItemValue):
"""Replaces the current item by the newItemValue.
Precondition: the list is not empty."""
if self.isEmpty():
raise AttributeError("Empty list has no next item")
temp = Node2Way(newItemValue)
temp.setNext(self._current.getNext())
temp.setPrevious(self._current.getPrevious())
self._current.getNext().setPrevious(temp)
self._current.getPrevious().setNext(temp)
self._current = temp
def insertBefore(self, item):
"""Inserts item before the current item, or
as the only item if the list is empty. The new item is the
current item."""
if self.isEmpty():
newNode = Node2Way(item)
newNode.setNext(self._trailer)
self._trailer.getPrevious(newNode)
newNode.setPrevious(self._header)
self._header.setNext(newNode)
self._size = 1
self._current = newNode
else:
temp = self._current.getPrevious()
newNode = Node2Way(item)
newNode.setNext(self._current)
self._current.setPrevious(newNode)
newNode.setPrevious(temp)
temp.setNext(newNode)
self._current = newNode
self._size += 1
def addRear(self, item, clock):
""" Adds item to the front of the Deque. """
temp = Node2Way(item, clock)
temp.setPrevious(self._rear)
if self._size == 0:
self._front = temp
else:
self._rear.setNext(temp)
self._rear = temp
self._size += 1
def insertBefore(self, item):
"""Inserts item before the current item, or
as the only item if the list is empty. The new item is the
current item."""
temp = Node2Way(item)
if self.isEmpty():
temp.setPrevious(self._header)
temp.setNext(self._trailer)
self._header.setNext(temp)
self._trailer.setPrevious(temp)
else:
temp.setNext(self._current)
self._current.getPrevious().setNext(temp)
temp.setPrevious(self._current.getPrevious())
self._current.setPrevious(temp)
self._current = temp
self._size += 1