def insert(self, key, data=None):
"""
Inserts a new node to the skip list.
Parameters
==========
key
Any valid identifier to uniquely
identify the node in the linked list.
data
Any valid data to be stored in the node.
"""
path = self._search(key)
tip = path[-1]
below = SkipNode(key=key, data=data, next=tip.next)
tip.next = below
total_level = self._levels
level = 1
while random.getrandbits(1) % 2 == 0 and level <= total_level:
if level == total_level:
self._add_level()
prev = self.head
else:
prev = path[total_level - 1 - level]
below = SkipNode(key=key, data=None, next=prev.next, down=below)
prev.next = below
level += 1
self._num_nodes += 1
def extract(self, key):
"""
Extracts the node with the given key in the skip list.
Parameters
==========
key
The key of the node under consideration.
Returns
=======
return_node: SkipNode
The node with given key.
"""
path = self._search(key)
tip = path[-1]
if tip.next.key != key:
raise KeyError('Node with key %s is not there in %s' % (key, self))
return_node = SkipNode(tip.next.key, tip.next.data)
total_level = self._levels
level = total_level - 1
while level >= 0 and path[level].next.key == key:
path[level].next = path[level].next.next
level -= 1
walk = self.head
while walk is not None:
if walk.next is self.tail:
self._levels -= 1
self.head = walk.down
self.tail = self.tail.down
walk = walk.down
else:
break
self._num_nodes -= 1
if self._levels == 0:
self._add_level()
return return_node
def _add_level(self):
self.tail = SkipNode(math.inf, next=None, down=self.tail)
self.head = SkipNode(-math.inf, next=self.tail, down=self.head)
self._levels += 1