我知道如何创建Link和LinearLinkedList类，但我不能为我的生活弄清楚如何将它们修改为创建循环链接列表。我已经阅读了这个问题的答案：Help with Circular Linked List in Python。但是，我不明白如果头部是None，那么无类型对象怎么能有＆＃34; next＆＃34;属性？我似乎无法掌握这个概念。 如果有人能够向我展示示例CircularLinkedList的 init 函数以及关于它如何工作的简单解释，我想我能够理解它。 感谢您的帮助
编辑：我只需要向前遍历列表。如果是这种情况，它背后的逻辑是否需要彻底改变？
答案 0 :(得分：6)
通常在循环链表中，您有一个不包含有意义数据的特殊链接。相反，它是一个＆＃34;哨兵＆＃34;让你知道列表的开头（和结束）在哪里。即使列表为空，此链接也将存在，因此您的算法将适用于所有列表，而不需要特殊代码的特殊情况。
class Link:
def __init__(self, data, next):
self.data = data
self.next = next
class CircularLinkedList:
def __init__(self):
self.head = Link(None, None) # this is the sentinel node!
self.head.next = self.head # link it to itself
def add(self, data): # no special case code needed for an empty list
self.head.next = Link(data, self.head.next)
def __contains__(self, data): # example algorithm, implements the "in" operator
current = self.head.next
while current != self.head:
if current.data == data: # element found
return True
current = current.next
return False
答案 1 :(得分：4)
实际上;如果没有节点，那么就没有下一个/前一个指针：
root
|
v
None
如果有一个节点，它会向后和向前链接：
root
|
v
+-> Node <-+
| next---+
+---prev
如果有两个节点：
root
|
v
+-> Node +-> Node <--+
| next---+ next--+ |
+-|---prev <-----prev | |
| +--------------------+ |
+------------------------+
答案 2 :(得分：1)
class Node:
def __init__(self, d=None, n=None, p=None):
self.data = d
self.next_node = n
self.p_node = p
def __str__(self):
return '(' + str(self.data) + ')'
class CircularlinkedList:
def __init__(self, r=None):
self.root = r
self.size = 0
def add(self, d):
if self.size == 0:
self.root = Node(d)
self.root.next_node = self.root
else:
new_node = Node(d, self.root.next_node)
self.root.next_node = new_node
self.size += 1
def find(self, d):
this_node = self.root
while True:
if this_node.data == d:
return d
elif this_node.next_node == self.root:
return False
this_node = this_node.next_node
def remove(self, d):
this_node = self.root
prev_node = None
while True:
if this_node.data == d:
if prev_node is not None:
prev_node.next_node = this_node.next_node
else:
while this_node.next_node != self.root:
this_node = this_node.next_node
this_node.next_node = self.root.next_node
self.root = self.root.next_node
self.size -= 1
return True
elif this_node.next_node == self.root:
return False
prev_node = this_node
this_node = this_node.next_node
def print_list(self):
if self.root is None:
return
this_node = self.root
print(this_node, end='->')
while this_node.next_node != self.root:
this_node = this_node.next_node
print(this_node, end='->')
print()
cll = CircularlinkedList（）
for i in [5, 7, 3, 8, 9]:
cll.add(i)
print（'Size ='+ str（cll.size））
print（cll.find（8））
print（cll.find（12））
my_node = cll.root
for i in range(8):
my_node = my_node.next_node
print(my_node,end='->')
print（）
cll.print_list（）
cll.remove（8）
print（cll.remove（15））
print（'Size ='+ str（cll.size））
cll.remove（5）
cll.print_list（）
答案 3 :(得分：0)
这里至关重要的一步是头部不是None。只有头部Link节点的数据为None，并且它通过其next属性指向自身。正如您所链接的答案所述，这看起来像这样：
def __init__(self):
self.head = Link(None, None)
self.head.next = self.head
答案 4 :(得分：0)
#Linked List Program to Add and Delete Node Form Head, Tail, in Between Nodes.
class Node:
""" Node Class having the data and pointer to the next Node"""
def __init__(self,value):
self.value=value
self.nextnode=None
class CircularLinkedList(object):
""" Linked List Class to point the value and the next nond"""
def __init__(self):
self.head=None
def add_head_node(self,value):
node=Node(value)
if self.head is None:
self.head=node
self.head.nextnode=self.head
crnt_node=node
crnt_node.nextnode=self.head
first_node=self.head
while first_node.nextnode is not self.head:
first_node=first_node.nextnode
first_node.nextnode=crnt_node
self.head=crnt_node
#Adding elements in linked list to the tail.
def add_tail_node(self,value):
node=Node(value)
if self.head is None:
self.head=node
self.head.nextnode=self.head
crnt_node=node
last_node=self.head
while last_node.nextnode is not self.head:
last_node=last_node.nextnode
#pointing head's last element to given node
last_node.nextnode=crnt_node
#pointing last node next to head nodes of element
crnt_node.nextnode=self.head
#Adding elements in linked after given Node.
def add_after_node(self,after_value,value):
node=Node(value)
if self.head is None:
self.head=node
self.head.nextnode=self.head
new_node=node
after_node=Node(after_value)
head_node=self.head
while head_node.value !=after_node.value:
head_node=head_node.nextnode
last_node=head_node.nextnode
head_node.nextnode=new_node
new_node.nextnode=last_node
head_node=head_node.nextnode
#Adding elements in linked before given Node.
def add_before_node(self,bfr_value,value):
node=Node(value)
if self.head is None:
self.head=node
self.head.nextnode=self.head
new_node=node
bfr_node=Node(bfr_value)
head_node=self.head
while head_node.nextnode.value!=bfr_node.value:
head_node=head_node.nextnode
last_node=head_node.nextnode
head_node.nextnode=new_node
new_node.nextnode=last_node
head_node=head_node.nextnode
#self.head=head_node.nextnode
#deleting Head Node of Linked List
def del_head_node(self):
if self.head is None:
print('Can not delete elements from Empty Linked List')
return
crnt_node=self.head.nextnode
pointer_head=self.head.nextnode
while pointer_head.nextnode.value!=self.head.value:
pointer_head=pointer_head.nextnode
pointer_head.nextnode=crnt_node
self.head=crnt_node
#deleting tail Node of Linked List
def del_tail_node(self):
if self.head is None:
print('Can not delete elements from Empty Linked List')
return
crnt_node=self.head.nextnode
#head_node=self.head
while crnt_node.nextnode.nextnode.value!=self.head.value:
crnt_node=crnt_node.nextnode
crnt_node.nextnode=self.head
#delete beteween node from Linked List
def del_bw_node(self,value):
node=Node(value)
if self.head is None:
print('Can not delete elements from Empty Linked List')
return
crnt_node=self.head
while crnt_node.nextnode.value!=node.value:
crnt_node=crnt_node.nextnode
last_node=crnt_node.nextnode.nextnode
crnt_node.nextnode=last_node
#Function to print linked list node
def print_list(self):
crnt_node=self.head
while True:
print(f'{crnt_node.value}->',end='')
if crnt_node.nextnode is self.head:
print(f'{self.head.value}',end='')
break
crnt_node = crnt_node.nextnode
print()
cir_llist=CircularLinkedList()
cir_llist.add_head_node(1)
cir_llist.print_list()
cir_llist.add_head_node(2)
cir_llist.print_list()
cir_llist.add_head_node(3)
cir_llist.print_list()
cir_llist.add_head_node(4)
cir_llist.print_list()
cir_llist.add_head_node(5)
cir_llist.print_list()
cir_llist.add_tail_node(6)
cir_llist.print_list()
cir_llist.add_tail_node(8)
cir_llist.print_list()
cir_llist.add_after_node(6,7)
cir_llist.print_list()
cir_llist.add_before_node(6,0)
cir_llist.print_list()
cir_llist.add_before_node(0,10)
cir_llist.print_list()
cir_llist.del_head_node()
cir_llist.print_list()
cir_llist.del_head_node()
cir_llist.print_list()
cir_llist.del_tail_node()
cir_llist.print_list()
cir_llist.del_tail_node()
cir_llist.print_list()
cir_llist.del_bw_node(10)
cir_llist.print_list()
cir_llist.del_bw_node(0)
cir_llist.print_list()