# coding:utf-8
# 单向循环链表的相关操作：
# is_empty() 判断链表是否为空
# length() 返回链表的长度
# travel() 遍历
# add(item) 在头部添加一个节点
# append(item) 在尾部添加一个节点
# insert(pos, item) 在指定位置pos添加节点
# remove(item) 删除一个节点
# search(item) 查找节点是否存在
class Node(object):
"""节点"""
def __init__(self, item):
self.elem = item
self.next = None
class SingleCycleLinkedList(object):
"""单向循环链表"""
def __init__(self, node=None):
self.__head = node
# 如果node不为空，则需要指向自己构成一个循环链表
if node:
node.next = node
def is_empty(self):
"""判断链表是否为空"""
return self.__head is None
def length(self):
"""返回链表的长度"""
if self.is_empty():
return 0
else:
cur = self.__head
count = 1
while cur.next is not self.__head:
count += 1
cur = cur.next
return count
def travel(self):
"""遍历"""
if self.is_empty():
return
else:
cur = self.__head
while cur.next is not self.__head:
print(cur.elem, end=" ")
cur = cur.next
# 循环结束，cur指向尾节点，但是尾节点元素尚未打印，需要单独输出
print(cur.elem)
def add(self, item):
"""在头部添加一个节点，头插法"""
node = Node(item)
if self.is_empty():
self.__head = node
node.next = node
else:
# 需要获取到尾节点
cur = self.__head
while cur.next is not self.__head:
cur = cur.next
node.next = self.__head
self.__head = node
cur.next = node
def append(self, item):
"""在尾部添加一个节点，尾插法"""
node = Node(item)
if self.is_empty():
self.__head = node
node.next = node
else:
# 同样需要获取到尾节点
cur = self.__head
while cur.next is not self.__head:
cur = cur.next
cur.next = node
node.next = self.__head
def insert(self, pos, item):
"""在指定位置pos添加节点"""
if pos <= 0:
self.add(item)
elif pos > (self.length() - 1):
self.append(item)
else:
node = Node(item)
prev = self.__head
count = 0
while count < pos - 1:
count += 1
prev = prev.next
# 循环结束，prev指向要插入位置的前一个元素
node.next = prev.next
prev.next = node
def remove(self, item):
"""删除一个节点，需要考虑链表是否为空，删除的节点是头节点，尾节点，还是中间节点"""
if self.is_empty():
return
else:
cur = self.__head
pre = None
while cur.next is not self.__head:
if cur.elem == item:
# 判断是头节点，还是中间节点
if cur is self.__head:
# 头节点，需要找到尾节点
rear = self.__head
while rear.next is not self.__head:
rear = rear.next
self.__head = cur.next
rear.next = self.__head
else:
# 中间节点
pre.next = cur.next
return
else:
pre = cur
cur = cur.next
# 退出循环，cur指向尾节点
if cur.elem == item:
# 注意判断链表中是否只有一个节点
if cur is 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
else:
cur = self.__head
while cur.next is not self.__head:
if cur.elem == item:
return True
else:
cur = cur.next
# 循环结束，cur指向尾节点，但是尾节点并未参与比较，需要单独进行判断的
if cur.elem == item:
return True
else:
return False
if __name__ == "__main__":
scll = SingleCycleLinkedList()
print("befor initialized:", scll.is_empty())
print("befor initialized:", scll.length())
scll.add(1)
scll.add(2)
scll.add(3)
scll.add(4)
scll.add(5)
scll.add(6)
scll.travel()
scll.append(7)
scll.travel()
scll.insert(3, 99)
scll.travel()
print("scll.search(99):", scll.search(99))
scll.remove(99)
scll.travel()
