python 数据结构之 双向链表 的定义以及类函数的定义:
class Node(object):
def __init__(self, data, prev_node=None, next_node=None):
self.data = data
self.prev_node = prev_node
self.next_node = next_node
def __repr__(self):
return str(self.data)
class DoublyLinkedList(object):
def __init__(self):
self.head = None
self.__count = 0
def is_empty(self):
return self.head is None
def __len__(self):
return self.__count
def add(self, data):
"""
Adds new Node containing data to head of the list
Also called prepend
Takes O(1) time
"""
new_head = Node(data, prev_node=None, next_node=self.head)
if not self.is_empty():
self.head.prev_node = new_head
self.head = new_head
self.__count += 1
def search(self, key):
"""
Search for the first node containing data that matches the key
Returns the node or `None` if not found
Takes O(n) time
"""
current = self.head
while current:
if current.data == key:
return current
else:
current = current.next_node
return None
def node_at_index(self, index):
"""
Returns the Node at specified index
Takes O(n) time
"""
if index >= self.__count:
raise IndexError('index out of range')
if index == 0:
return self.head
current = self.head
'''
position = 0
while position < index:
current = current.next_node
position += 1
'''
while index:
current = current.next_node
index -= 1
return current
def insert(self, data, index):
"""
Inserts a new Node containing data at index position
Insertion takes O(1) time but finding node at insertion point takes
O(n) time.
Takes overall O(n) time.
"""
if index >= self.__count:
raise IndexError('index out of range')
if index == 0:
self.add(data)
return
if index > 0:
current_node = self.node_at_index(index)
prev_node = current_node.prev_node
new_node = Node(data, prev_node=prev_node, next_node=current_node)
current_node.prev_node = new_node
prev_node.next_node = new_node
self.__count += 1
def remove(self, key):
"""
Removes Node containing data that matches the key
Returns the node or `None` if key doesn't exist
Takes O(n) time
"""
current = self.head
found = False
while current and not found:
if current.data == key and current is self.head:
found = True
self.head = current.next_node
self.head.prev_node = None
self.__count -= 1
return current
elif current.data == key:
found = True
prev_node = current.prev_node
next_node = current.next_node
prev_node.next_node = next_node
next_node.prev_node = prev_node
self.__count -= 1
return current
else:
current = current.next_node
def remove_at_index(self, index):
"""
Removes Node at specified index
Takes O(n) time
"""
if index >= self.__count:
raise IndexError('index out of range')
current = self.head
if index == 0:
self.head = current.next_node
self.head.prev_node = None
self.__count -= 1
return current
current = self.node_at_index(index)
prev_node = current.prev_node
next_node = current.next_node
prev_node.next_node = next_node
next_node.prev_node = prev_node
self.__count -= 1
return current
def __iter__(self):
current = self.head
while current:
yield current
current = current.next_node
def __repr__(self):
"""
Return a string representation of the list.
Takes O(n) time.
"""
nodes = []
current = self.head
while current:
if current is self.head:
nodes.append("[Head: %s]" % current.data)
elif current.next_node is None:
nodes.append("[Tail: %s]" % current.data)
else:
nodes.append("[%s]" % current.data)
current = current.next_node
return ' <=> '.join(nodes)
if __name__ == '__main__':
dll_1 = DoublyLinkedList()
dll_1.add(1)
dll_1.add(2)
dll_1.add(3)
dll_1.add(4)
dll_1.insert(5, 2)
print(dll_1)
运行结果:
[Head: 4] <=> [3] <=> [5] <=> [2] <=> [Tail: 1]
