前言
本篇章主要介绍线性表中的循环单链表，并用Python实现其基本操作。
1. 循环单链表
循环单链表是在单链表的基础之上，将单链表的头结点地址存入了最后一个结点的指针域，即最后一个结点的next指针域不再是None，而是指向了头结点，所以循环单链表可以从表中的任意一个结点开始遍历整个链表。其他操作和单链表是一样的。
2. 基本操作
| 操作名称 | 操作说明 |
|---|---|
| InsertInHead(val_list) | 头插法创建循环单链表 |
| InsertInTail(val_list) | 尾插法创建循环单链表 |
| IsEmpty() | 判断循环单链表是否为空 |
| LengthList() | 返回循环单链表的长度 |
| TraverseList() | 打印出循环单链表里的数据元素 |
| InsertInPosition(pos, data) | 在指定位置插入 |
| SearchWithPosition(pos) | 按位置查找结点 |
| SearchWithVal(data) | 按值查找结点 |
| RemoveWithPosition(pos) | 移除指定位置的结点 |
| RemoveWithVal(data) | 移除指定值的结点 |
3. 代码实现
class CircularSingleLinkList(object):
"""
与单链表不同的是, 循环单链表的最后一个节点的next指向头结点
"""
def __init__(self):
self.__head = LinkNode(None)
self.__head.next = self.__head
def InsertInHead(self, val_list):
"""
头插法
:param val_list:
:return:
"""
prehead = self.__head
for val in val_list:
new_node = LinkNode(val)
if self.IsEmpty():
prehead.next = new_node
new_node.next = self.__head
else:
new_node.next = prehead.next
prehead.next = new_node
def InsertInTail(self, val_list):
"""
尾插法
:param val_list:
:return:
"""
prehead = self.__head
for val in val_list:
new_node = LinkNode(val)
prehead.next = new_node
new_node.next = self.__head
prehead = prehead.next
def IsEmpty(self):
"""
判断循环单链表是否为空, 空返回true
:return:
"""
if self.__head.next == self.__head:
return True
def LengthList(self):
"""
返回循环单链表的长度
:return:
"""
prehead = self.__head
count = 0
if self.IsEmpty():
return count
while prehead.next != self.__head:
count += 1
prehead = prehead.next
return count
def TraverseList(self):
"""
遍历循环单链表, 并打印
:return:
"""
prehead = self.__head
if self.IsEmpty():
print('链表为空!')
return 0
while prehead.next != self.__head:
prehead = prehead.next
print(prehead.data, end=' ')
print('')
def InsertInPosition(self, pos, data):
"""
按位置插入
:param pos: [1, LengthCircularSingleLinkList + 1]
:param data:
:return:
"""
prehead = self.__head
new_node = LinkNode(data)
if pos <= 0 or pos > self.LengthList() + 1:
print('插入位置错误!')
return 0
count = 0
while count < pos - 1:
prehead = prehead.next
count += 1
new_node.next = prehead.next
prehead.next = new_node
def SearchWithPosition(self, pos):
"""
按位置查找元素
:param pos: [1, LengthSingleLinkList]
:return:
"""
prehead = self.__head
if pos <= 0 or pos > self.LengthList():
print('位置错误!')
return -1
count = 0
while count < pos:
prehead = prehead.next
count += 1
data = prehead.data
return data
def SearchWithVal(self, data):
"""
按值查找元素
:param data:
:return:
"""
prehead = self.__head
count = 0
while prehead.next != self.__head:
prehead = prehead.next
count += 1
if prehead.data == data:
return count
print('该节点不存在!')
return -1
def RemoveWithPosition(self, pos):
"""
按位置移除元素
:param pos: [1, LengthSingleLinkList]
:return:
"""
prehead = self.__head
if pos <= 0 or pos > self.LengthList():
print('位置错误!')
return -1
count = 0
while count < pos - 1:
prehead = prehead.next
count += 1
temp = prehead.next
prehead.next = temp.next
del temp
def RemoveWithVal(self, data):
"""
按值移除元素(所有的)
:param data:
:return:
"""
prehead = self.__head
while prehead.next != self.__head:
prev = prehead
prehead = prehead.next
if prehead.data == data:
prev.next = prehead.next
return -1
print('该节点不存在!')
def RemoveWithValAll(self, data):
"""
按值移除元素(所有的)
:param data:
:return:
"""
prehead = self.__head
count = True
while prehead.next != self.__head:
prev = prehead
prehead = prehead.next
if prehead.data == data:
prev.next = prehead.next
count = False
if count:
print('该节点不存在!')
测试代码如下：
from LinkList import CircularSingleLinkList
if __name__ == '__main__':
l1 = CircularSingleLinkList()
print('头插法创建循环单链表l1: ', end='')
l1.InsertInHead([1, 3, 5, 7, 9, 10])
l1.TraverseList()
l2 = CircularSingleLinkList()
print('尾插法创建循环单链表l2: ', end='')
l2.InsertInTail([1, 3, 5, 7, 9, 10])
l2.TraverseList()
print('链表l2的长度为: %d' % l2.LengthList())
print('在链表l2的第3个位置上插入值为2的节点: ', end='')
l2.InsertInPosition(3, 2)
l2.TraverseList()
print('链表l2的第4个位置上的节点的值为: %d' % l2.SearchWithPosition(4))
print('链表l2值为9的节点的位置为: %d' % l2.SearchWithVal(9))
print('移除链表l2的第5个位置上的节点: ', end='')
l2.RemoveWithPosition(5)
l2.TraverseList()
print('移除链表l2值为1的节点: ', end='')
l2.RemoveWithVal(1)
l2.TraverseList()
运行结果如下：
结束语
循环单链表需要注意的就是尾结点的next指针域，所以在判别是不是尾结点的时候要注意这一点。当然，正是因为循环单链表是一个“环”，因此在任一位置上的插入和删除操作都是等价的，也就不需要刻意去判断是否是表尾了。