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 = itemself.next = Noneclass SinCycLinkedlist(object):"""单向循环链表"""def __init__(self):self._head = Nonedef is_empty(self):"""判断链表是否为空"""return self._head == Nonedef length(self):"""返回链表的长度"""# 如果链表为空，返回长度0if self.is_empty():return 0count = 1cur = self._headwhile cur.next != self._head:count += 1cur = cur.nextreturn countdef travel(self):"""遍历链表"""if self.is_empty():returncur = self._headprint cur.item,while cur.next != self._head:cur = cur.nextprint cur.item,print ""def add(self, item):"""头部添加节点"""node = Node(item)if self.is_empty():self._head = nodenode.next = self._headelse:#添加的节点指向_headnode.next = self._head# 移到链表尾部，将尾部节点的next指向nodecur = self._headwhile cur.next != self._head:cur = cur.nextcur.next = node#_head指向添加node的self._head = nodedef append(self, item):"""尾部添加节点"""node = Node(item)if self.is_empty():self._head = nodenode.next = self._headelse:# 移到链表尾部cur = self._headwhile cur.next != self._head:cur = cur.next# 将尾节点指向nodecur.next = node# 将node指向头节点_headnode.next = self._headdef 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._headcount = 0# 移动到指定位置的前一个位置while count < (pos-1):count += 1cur = cur.nextnode.next = cur.nextcur.next = nodedef 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._headpre = None# 若头节点的元素就是要查找的元素itemif cur.item == item:# 如果链表不止一个节点if cur.next != self._head:# 先找到尾节点，将尾节点的next指向第二个节点while cur.next != self._head:cur = cur.next# cur指向了尾节点cur.next = self._head.nextself._head = self._head.nextelse:# 链表只有一个节点self._head = Noneelse:pre = self._head# 第一个节点不是要删除的while cur.next != self._head:# 找到了要删除的元素if cur.item == item:# 删除pre.next = cur.nextreturnelse:pre = curcur = cur.next# cur 指向尾节点if cur.item == item:# 尾部删除pre.next = cur.nextdef search(self, item):"""查找节点是否存在"""if self.is_empty():return Falsecur = self._headif cur.item == item:return Truewhile cur.next != self._head:cur = cur.nextif cur.item == item:return Truereturn Falseif __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()

输出：

length: 6
6
2
1
4
3
5True
False
length: 5
6
2
4
3
5