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* Upgrade to Python 3.8 syntax
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144 lines
4.0 KiB
Python
144 lines
4.0 KiB
Python
"""
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Implementing Deque using DoublyLinkedList ...
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Operations:
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1. insertion in the front -> O(1)
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2. insertion in the end -> O(1)
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3. remove from the front -> O(1)
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4. remove from the end -> O(1)
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"""
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class _DoublyLinkedBase:
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""" A Private class (to be inherited) """
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class _Node:
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__slots__ = "_prev", "_data", "_next"
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def __init__(self, link_p, element, link_n):
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self._prev = link_p
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self._data = element
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self._next = link_n
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def has_next_and_prev(self):
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return " Prev -> {}, Next -> {}".format(
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self._prev is not None, self._next is not None
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)
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def __init__(self):
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self._header = self._Node(None, None, None)
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self._trailer = self._Node(None, None, None)
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self._header._next = self._trailer
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self._trailer._prev = self._header
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self._size = 0
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def __len__(self):
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return self._size
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def is_empty(self):
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return self.__len__() == 0
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def _insert(self, predecessor, e, successor):
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# Create new_node by setting it's prev.link -> header
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# setting it's next.link -> trailer
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new_node = self._Node(predecessor, e, successor)
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predecessor._next = new_node
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successor._prev = new_node
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self._size += 1
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return self
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def _delete(self, node):
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predecessor = node._prev
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successor = node._next
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predecessor._next = successor
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successor._prev = predecessor
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self._size -= 1
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temp = node._data
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node._prev = node._next = node._data = None
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del node
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return temp
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class LinkedDeque(_DoublyLinkedBase):
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def first(self):
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"""return first element
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>>> d = LinkedDeque()
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>>> d.add_first('A').first()
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'A'
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>>> d.add_first('B').first()
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'B'
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"""
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if self.is_empty():
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raise Exception("List is empty")
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return self._header._next._data
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def last(self):
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"""return last element
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>>> d = LinkedDeque()
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>>> d.add_last('A').last()
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'A'
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>>> d.add_last('B').last()
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'B'
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"""
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if self.is_empty():
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raise Exception("List is empty")
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return self._trailer._prev._data
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# DEque Insert Operations (At the front, At the end)
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def add_first(self, element):
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"""insertion in the front
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>>> LinkedDeque().add_first('AV').first()
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'AV'
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"""
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return self._insert(self._header, element, self._header._next)
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def add_last(self, element):
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"""insertion in the end
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>>> LinkedDeque().add_last('B').last()
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'B'
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"""
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return self._insert(self._trailer._prev, element, self._trailer)
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# DEqueu Remove Operations (At the front, At the end)
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def remove_first(self):
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"""removal from the front
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>>> d = LinkedDeque()
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>>> d.is_empty()
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True
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>>> d.remove_first()
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Traceback (most recent call last):
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...
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IndexError: remove_first from empty list
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>>> d.add_first('A') # doctest: +ELLIPSIS
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<data_structures.linked_list.deque_doubly.LinkedDeque object at ...
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>>> d.remove_first()
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'A'
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>>> d.is_empty()
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True
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"""
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if self.is_empty():
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raise IndexError("remove_first from empty list")
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return self._delete(self._header._next)
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def remove_last(self):
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"""removal in the end
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>>> d = LinkedDeque()
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>>> d.is_empty()
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True
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>>> d.remove_last()
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Traceback (most recent call last):
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...
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IndexError: remove_first from empty list
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>>> d.add_first('A') # doctest: +ELLIPSIS
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<data_structures.linked_list.deque_doubly.LinkedDeque object at ...
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>>> d.remove_last()
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'A'
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>>> d.is_empty()
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True
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"""
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if self.is_empty():
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raise IndexError("remove_first from empty list")
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return self._delete(self._trailer._prev)
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