双向链表
一种更复杂的链表是“双向链表”或“双面链表”。每个节点有两个链接：一个指向前一个节点，当此节点为第一个节点时，指向空值；而另一个指向下一个节点，当此节点为最后一个节点时，指向空值。
图片.png
操作
- is_empty() 链表是否为空
- length() 链表长度
- travel() 遍历链表
- add(item) 链表头部添加
- append(item) 链表尾部添加
- insert(pos, item) 指定位置添加
- remove(item) 删除节点
- search(item) 查找节点是否存在
实现
# coding:utf-8
class Node(object):
"""结点"""
def __init__(self, item):
self.elem = item
self.next = None
self.prev = None
class DoubleLinkList(object):
"""双链表"""
def __init__(self, node=None):
self.__head = node
def is_empty(self):
"""链表是否为空"""
return self.__head == None
def length(self):
"""链表长度"""
# cur游标，用来移动遍历节点
cur = self.__head
# count记录数量
count = 0
while cur != None:
count += 1
cur = cur.next
return count
def travel(self):
"""遍历整个链表"""
cur = self.__head
while cur != None:
print(cur.elem, end=" ")
cur = cur.next
print("")
def add(self, item):
"""链表头部添加元素，头插法"""
node = Node(item)
if self.is_empty():
self.__head = node
return
node.next = self.__head
self.__head = node
node.next.prev = node
def append(self, item):
"""链表尾部添加元素, 尾插法"""
node = Node(item)
if self.is_empty():
self.__head = node
else:
cur = self.__head
while cur.next != None:
cur = cur.next
cur.next = node
node.prev = cur
def insert(self, pos, item):
"""指定位置添加元素
:param pos 从0开始
"""
if pos <= 0:
self.add(item)
elif pos > (self.length()-1):
self.append(item)
else:
cur = self.__head
count = 0
while count < pos:
count += 1
cur = cur.next
# 当循环退出后，cur指向pos位置
node = Node(item)
node.next = cur
node.prev = cur.prev
cur.prev.next = node
cur.prev = node
def remove(self, item):
"""删除节点"""
cur = self.__head
while cur != None:
if cur.elem == item:
# 先判断此结点是否是头节点
# 头节点
if cur == self.__head:
self.__head = cur.next
if cur.next:
# 判断链表是否只有一个结点
cur.next.prev = None
else:
cur.prev.next = cur.next
if cur.next:
cur.next.prev = cur.prev
break
else:
cur = cur.next
def search(self, item):
"""查找节点是否存在"""
cur = self.__head
while cur != None:
if cur.elem == item:
return True
else:
cur = cur.next
return False
if __name__ == "__main__":
ll = DoubleLinkList()
print(ll.is_empty())
print(ll.length())
ll.append(1)
print(ll.is_empty())
print(ll.length())
ll.append(2)
ll.add(8)
ll.append(3)
ll.append(4)
ll.append(5)
ll.append(6)
# 8 1 2 3 4 5 6
ll.insert(-1, 9) # 9 8 1 23456
ll.travel()
ll.insert(3, 100) # 9 8 1 100 2 3456
ll.travel()
ll.insert(10, 200) # 9 8 1 100 23456 200
ll.travel()
ll.remove(100)
ll.travel()
ll.remove(9)
ll.travel()
ll.remove(200)
ll.travel()
