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单向循环链表
单链表的一个变形是单向循环链表，链表中最后一个节点的next域不再为None，而是指向链表的头节点。
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
实现
class Node(object):
"""节点"""
def __init__(self, item):
self.item = item
self.next = None
class SinCycLinkedlist(object):
"""单向循环链表"""
def __init__(self):
self.__head = None
def is_empty(self):
"""判断链表是否为空"""
return self.__head == None
def length(self):
"""返回链表的长度"""
# 如果链表为空，返回长度0
if self.is_empty():
return 0
count = 1
cur = self.__head
while cur.next != self.__head:
count += 1
cur = cur.next
return count
def travel(self):
"""遍历链表"""
if self.is_empty():
return
cur = self.__head
print cur.item,
while cur.next != self.__head:
cur = cur.next
print cur.item,
print ""
def add(self, item):
"""头部添加节点"""
node = Node(item)
if self.is_empty():
self.__head = node
node.next = self.__head
else:
#添加的节点指向_head
node.next = self.__head
# 移到链表尾部，将尾部节点的next指向node
cur = self.__head
while cur.next != self.__head:
cur = cur.next
cur.next = node
#_head指向添加node的
self.__head = node
def append(self, item):
"""尾部添加节点"""
node = Node(item)
if self.is_empty():
self.__head = node
node.next = self.__head
else:
# 移到链表尾部
cur = self.__head
while cur.next != self.__head:
cur = cur.next
# 将尾节点指向node
cur.next = node
# 将node指向头节点_head
node.next = self.__head
def insert(self, pos, item):
"""在指定位置添加节点"""
if pos <= 0:
self.add(item)
elif pos > (self.length()-1):
self.append(item)
else:
node = Node(item)
cur = self.__head
count = 0
# 移动到指定位置的前一个位置
while count < (pos-1):
count += 1
cur = cur.next
node.next = cur.next
cur.next = node
def remove(self, item):
"""删除一个节点"""
# 若链表为空，则直接返回
if self.is_empty():
return
# 将cur指向头节点
cur = self.__head
pre = None
while cur.next != self.__head:
if cur.item == item:
# 先判断此结点是否是头节点
if cur == self.__head:
# 头节点的情况
# 找尾节点
rear = self.__head
while rear.next != 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.item == item:
if cur == self.__head:
# 链表只有一个节点
self.__head = None
else:
# pre.next = cur.next
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
if cur.item == item:
return True
while cur.next != self.__head:
cur = cur.next
if cur.item == item:
return True
return False
if __name__ == "__main__":
ll = SinCycLinkedlist()
ll.add(1)
ll.add(2)
ll.append(3)
ll.insert(2, 4)
ll.insert(4, 5)
ll.insert(0, 6)
print "length:",ll.length()
ll.travel()
print ll.search(3)
print ll.search(7)
ll.remove(1)
print "length:",ll.length()
ll.travel()
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