如何在Python中反转循环链表
我有一个循环链表对象,我正在练习,我被困在了必须反转循环链表的地方。我可以找到很多使用Java&C的示例,但没有python示例。我试图转换C和Java程序的逻辑,但结果不正确。它只收集了列表的一部分,似乎提前终止 以下是我迄今为止定义如何在Python中反转循环链表,python,data-structures,circular-list,Python,Data Structures,Circular List,我有一个循环链表对象,我正在练习,我被困在了必须反转循环链表的地方。我可以找到很多使用Java&C的示例,但没有python示例。我试图转换C和Java程序的逻辑,但结果不正确。它只收集了列表的一部分,似乎提前终止 以下是我迄今为止定义节点和循环列表对象的代码: class Node(object): def __init__(self, data = None, next_node = None): self.data = data self.next
节点和循环列表
对象的代码:
class Node(object):
def __init__(self, data = None, next_node = None):
self.data = data
self.next_node = next_node
class CircularLinkedList(object):
def __init__(self, head = None, end = None):
self.head = head
self.end = end
def traverse(self):
curr_node = self.head
while curr_node.next_node:
print(curr_node.data)
curr_node = curr_node.next_node
if curr_node == self.head:
break
def insert_end(self, data):
new_node = Node(data)
# handle empty list case
if self.head == None:
self.head = new_node
self.head.next_node = new_node
self.end = new_node
return
# handle non-empty list case
if self.end != None:
self.end.next_node = new_node
new_node.next_node = self.head
self.end = new_node
return
def insert_beg(self, data):
new_node = Node(data)
new_node.next_node = self.head
curr_node = self.head
# handle empty list case
if curr_node == None:
self.head = new_node
self.end = new_node
self.head.next_node = new_node
return
# handle non-empty list case
if self.end != None:
self.end.next_node = new_node
new_node.next_node = self.head
self.head = new_node
return
def insert_mid(self, ref_node, data):
# handle empty node case
if ref_node == None:
print("You've selected an empty node.")
# if we are inserting after the end node, then just use the insert_end method
if ref_node == self.end:
self.insert_end(data)
return
# otherwise it's a true mid.
new_node = Node(data)
ref_next = ref_node.next_node
ref_node.next_node = new_node
new_node.next_node = ref_next
def delete_beg(self):
if self.head != None:
aft_head = self.head.next_node
self.end.next_node = aft_head
self.head = aft_head
else:
print('The list is empty, no values to delete.')
def delete_end(self):
if self.end != None:
curr_node = self.head
while curr_node.next_node.next_node != self.head:
curr_node = curr_node.next_node
self.end = curr_node
curr_node.next_node = self.head
def delete_mid(self, position):
if position == 0:
self.delete_beg()
return
if position == self.list_size():
self.delete_end()
return
curr_node = self.head.next_node
count = 0
while count <= position:
count = count + 1
curr_node = curr_node.next_node
curr_node.next_node = curr_node.next_node.next_node
def list_size(self):
curr_node = self.head
count = 0
while curr_node.next_node:
count = count + 1
curr_node = curr_node.next_node
if curr_node == self.head:
break
return count
以下是我的代码的主要部分,其中插入和删除值,然后尝试反转列表:
# define a new list
circular_list = CircularLinkedList()
# insert a few values at the end
circular_list.insert_end(50)
circular_list.insert_end(60)
circular_list.insert_end(70)
# insert a few values at the beginning
circular_list.insert_beg(90)
circular_list.insert_beg(100)
# grab a node
first_node = circular_list.end
# insert value inbetween two nodes.
circular_list.insert_mid(first_node,20)
# delete the first and last value
circular_list.delete_beg()
circular_list.delete_end()
print('Before Reversal')
print('-'*20)
circular_list.traverse()
circular_list.reverse()
print('After Reversal')
print('-'*20)
circular_list.traverse()
但当我尝试反转时,这是输出:
def reverse(self):
if self.head == None:
return
last = self.head
prev = self.head
curr = self.head.next_node
while self.head != last:
self.head = self.head.next_node
curr.next_node = prev
prev = curr
curr = self.head
curr.next_node = prev
self.head = prev
Before Reversal
--------------------
90
50
60
70
After Reversal
--------------------
90
50
通过查看您的代码,reverse()函数肯定有一个bug。
您可以很容易地看到,您从未开始while循环迭代,因为条件在开始时为false。我会这样做:
def reverse(self):
if self.head == None:
return
last = self.head
curr = self.head
prev = self.end
next=curr.next_node
curr.next_node = prev
prev = curr
curr = next
while curr != last:
next=curr.next_node
curr.next_node = prev
prev = curr
curr = next
在反向
中,while
循环中的条件永远无法满足,因为您刚刚将上次
初始化为等于self.head
。这意味着循环体永远不会运行,因此您只需要处理几个节点,而不是整个列表。是否应该将last
初始化为self.end
呢?因此,如果我将last
更改为self.end
我会得到一个永不终止的无限循环。这对我来说没有意义,因为如果我在while
循环中重新分配self.head
,它最终应该等于最后一个节点。正如@Bickknght已经指出的,所有这些操作都是将第二个节点链接回第一个节点。我不清楚你的算法——你在圆圈周围迭代head
,而'last'没有改变(迭代的最后一个元素?)。你的代码工作得很好,我唯一添加的是curr.next_node=prev
和self.head=prev
,最后它重新分配了head节点。