双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。
双链表和单链表在查找和遍历上没什么区别，在新增节点、添加节点、删除节点上需要注意前后节点的修改，比单链表会复杂一些，一不小心就绕晕了。
方法和单链表是一致的。
isempty(self) 链表是否为空
length(self) 链表长度
travel(self) 遍历整个链表
add(self,item) 链表头部添加元素
append(self,item) 链表尾部添加元素
insert(self,item,index) 指定位置添加元素
deletebyitem(self,item) 根据数据项删除节点
deletebyindex(self,index) 根据索引位置删除节点
search(self,item) 根据数据项查找节点是否存在
update(self,index,item) 暂无实现
getitem(self,index) 获取索引位置对应的数据项
getindex(self,item) 获取数据项对应的索引位置
如下：
#!/usr/bin/env python
# -*- coding: UTF-8 -*-
# _ooOoo_
# o8888888o
# 88" . "88
# ( | - _ - | )
# O\ = /O
# ____/`---'\____
# .' \\| |// `.
# / \\|||:|||// \
# / _|||||-:- |||||- \
# | | \\\ - /// | |
# | \_| ''\---/'' | _/ |
# \ .-\__ `-` ___/-. /
# ___`. .' /--.--\ `. . __
# ."" '< `.___\_<|>_/___.' >'"".
# | | : `- \`.;`\ _ /`;.`/ - ` : | |
# \ \ `-. \_ __\ /__ _/ .-` / /
# ==`-.____`-.___\_____/___.-`____.-'==
# `=---='
'''
@Project ：pythonalgorithms
@File ：doublelinklist.py
@Author ：不胜人生一场醉
@Date ：2021/7/13 23:00
'''
class Node(object):
def __init__(self, data):
self.prev = None
self.data = data
self.next = None
class DoubleLinkList(object):
def __init__(self):
self.header = None
self.currentnum = 0
def isempty(self):
return self.header == None
def travel(self):
tempnode = self.header
while tempnode != None:
print("{}".format(tempnode.data), end=" ")
tempnode = tempnode.next
print("\r")
def add(self, item):
node = Node(item)
if self.isempty():
self.header = node
self.currentnum += 1
return
node.next = self.header
self.header.prev = node
self.header = node
self.currentnum += 1
def append(self, item):
if self.isempty():
self.add(item)
self.currentnum += 1
return
tempnode = self.header
while tempnode.next is not None:
tempnode = tempnode.next
node = Node(item)
node.prev = tempnode
tempnode.next = node
self.currentnum += 1
def length(self):
length = 0
tempnode = self.header
while tempnode is not None:
length += 1
tempnode = tempnode.next
return length
def search(self, item):
tempnode = self.header
while tempnode != None:
if tempnode.data == item:
return True
else:
tempnode = tempnode.next
return False
def update(self, index, item):
pass
def getitem(self, index):
if index > self.currentnum or index <= 0:
raise IndexError("{} is not find in Linklist".format(index))
tempnode = self.header
i = 1
while i < index:
tempnode = tempnode.next
i += 1
if tempnode.next == None:
return -1
else:
return tempnode.data
def getindex(self, item):
tempnode = self.header
i = 0
flag = False
while tempnode != None:
i += 1
if tempnode.data == item:
flag = True
return i
else:
tempnode = tempnode.next
if flag == False:
return 0
def insert(self, item, index):
tempnode = self.header
if index > self.currentnum + 1 or index <= 0:
raise IndexError("{} is not find in Linklist".format(index))
# 指定位置为第一个即在头部插入
if index == 1:
self.add(item)
elif index > self.currentnum - 1:
self.append(item)
else:
node = Node(item)
for i in range(1, index - 1):
tempnode = tempnode.next
node.next = tempnode.next
node.prev = tempnode
tempnode.next.prev = node
tempnode.next = node
self.currentnum += 1
def deletebyitem(self, item):
tempnode = self.header
while tempnode != None:
if tempnode.data == item:
self.currentnum -= 1
if tempnode == self.header:
self.header = self.header.next
if tempnode.next:
tempnode.next.prev = None
return
if tempnode.next is None:
tempnode.prev.next = tempnode.next
return
tempnode.prev.next = tempnode.next
tempnode.next.prev = tempnode.prev
return
tempnode = tempnode.next
def deletebyindex(self, index):
if index > self.currentnum or index <= 0:
raise IndexError("{} is not find in Linklist".format(index))
i = 1
tempnode = self.header
if index == 1:
self.header = tempnode.next
if tempnode.next:
tempnode.prev = None
self.currentnum -= 1
return
while tempnode.next and i < index:
tempnode = tempnode.next
i += 1
if tempnode.next is None:
tempnode.prev.next = tempnode.next
self.currentnum -= 1
return
if i == index:
tempnode.prev.next = tempnode.next
tempnode.next.prev = tempnode.prev
self.currentnum -= 1
if __name__ == '__main__':
a = DoubleLinkList()
a.add(1) # 1
a.travel()
a.add(2)
a.travel()
a.append(4)
a.travel()
a.append(3)
a.travel()
print(a.length())
print(a.search(1))
print(a.getindex(4))
print(a.getindex(5))
print(a.getitem(2))
# print(a.getitem(5))
# IndexError: 5 is not find in Linklist
a.insert(5, 1)
a.travel()
a.insert(6, 5)
a.travel()
a.insert(7, 2)
a.travel()
a.deletebyitem(7)
a.travel()
a.deletebyitem(6)
a.travel()
a.deletebyitem(5)
a.travel()
a.deletebyindex(2)
a.travel()
a.deletebyindex(3)
a.travel()
a.deletebyindex(1)
a.travel()
调试了2、3个小时的bug，才跑通。
运行如下：
C:\python\pyproject\pythonalgorithms\venv\Scripts\python.exe C:/python/pyproject/pythonalgorithms/doublelinklist.py
1
2 1
2 1 4
2 1 4 3
4
True
3
0
1
5 2 1 4 3
5 2 1 4 6 3
5 7 2 1 4 6 3
5 2 1 4 6 3
5 2 1 4 3
2 1 4 3
2 4 3
2 4
4
Process finished with exit code 0
链表头部增加节点示意图
