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class Node(object):

"""节点类"""

def __init__(self, item):

self.item = item # 数据区

self.next = None # 链接区

self.pre = None

class CycleSingleLinkList(object):

"""单向循环链表"""

def __init__(self, node=None):

self.__head = node def is_empty(self):

""" 链表是否为空

:return 如果链表为空，返回真

"""

return self.__head is None def length(self):

"""链表长度"""

if self.is_empty():

return 0

# 将cur这个游标指向链表的头信息

cur = self.__head

count = 1

while cur.next != self.__head:

count += 1

cur = cur.next

return count def travel(self):

"""遍历整个链表"""

if self.is_empty():

print("")

return

cur = self.__head

while cur.next != self.__head:

print(cur.item, end=" ")

cur = cur.next

# 从循环退出,cur指向尾节点

print(cur.item) def add(self, item):

"""链表头部添加元素

:param item:要保存的具体数据"""

node = Node(item)

if self.is_empty():

self.__head = node

node.next = node

# 寻找尾节点

cur = self.__head

while cur.next != self.__head:

cur = cur.next

# 从循环退出，cur指向尾节点

node.next = self.__head

self.__head = node

cur.next = self.__head def append(self, item):

"""链表尾部添加元素"""

node = Node(item)

# 如果链表为空，需要特殊处理

if self.is_empty():

self.__head = node

else:

cur = self.__head

while cur.next != self.__head:

cur = cur.next

# 退出循环的时候，cur指向的尾节点

cur.next = node

node.next = self.__head def insert(self, pos, item):

"""指定位置添加元素"""

node = Node(item)

# 在头部添加元素

if pos <= 0:

self.add(item)

# 在尾部添加元素

elif pos >= self.length():

self.append(item)

else:

cur = self.__head

count = 0

while count < (pos-1):

count += 1

cur = cur.next

# 退出循环的时候，cur指向pos的前一个位置

node.next = cur.next

cur.next = node def remove(self,item):

"""删除节点"""

cur = self.__head

pre = None

while cur.next != self.__head:

# 找到要删除的元素

if cur.item == item:

# 在头部找到了要删除的元素

if cur == self.__head:

# 先找到尾节点

rear = self.__head

while rear.next != self.__head:

rear = rear.next

# 退出循环后，rear指向尾节点

self.__head = cur.next

rear.next = self.__head

# 在中间找到元素

else:

pre.next = cur.next

return

# 不是要找的元素，移动游标

pre = cur

cur = cur.next

# 退出循环后，cur指向尾节点

if cur.item == item:

# 链表只有一个节点：

if cur == self.__head:

self.__head = None

else:

pre.next = self.__head def search(self, item):

"""查找节点是否存在"""

if self.is_empty():

return False

cur = self.__head

while cur.next != self.__head:

if cur.item == item:

return True

cur = cur.next

# 退出循环后，cur指向尾节点

if cur.item == item:

return True

return False

if __name__ == '__main__':

ll = CycleSingleLinkList()

print(ll.length())

ll.travel() ll.append(1)

print(ll.length())

ll.travel() ll.append(2)

ll.travel() ll.add(3)

ll.travel() ll.insert(0, 4)

ll.travel() ll.insert(19, 5)

ll.travel() ll.insert(2, 6)

ll.travel() ll.remove(4)

ll.travel() ll.remove(5)

ll.travel() ll.remove(6)

ll.travel() ll.remove(3)

ll.travel() ll.remove(2)

ll.travel() ll.remove(1)

ll.travel()Traceback (most recent call last):

File "D:/Item/DataStructure/code/03_cycle_single_link_list.py", line 145, in

print(ll.length())

0

File "D:/Item/DataStructure/code/03_cycle_single_link_list.py", line 27, in length

while cur.next != self.__head:

AttributeError: 'NoneType' object has no attribute 'next'

Process finished with exit code 1