python描述单向循环链表

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单链表的一个变形就是单向循环链表，链表中最后一个节点的next域不在为None，而是指向链表的头节点

操作

is_empty() 判空
length() 求长度
travel() 遍历
add(item) 头部插入
append(item) 尾部插入
insert(pos,item) 在指定位置插入
remove(item) 删除一个节点
search(item) 查找一个节点是否存在

实现

class Node(object):    """节点"""    def __init__(self,item):        self.item = item        self.next = Noneclass 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node            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            # 将尾节点的next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        # 若头节点的元素就是要查找的元素item        if 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.next                self._head = self._head.next            else:                # 链表只有一个节点                self._head = None        else:            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.next                    return                else:                    pre = cur                    cur = cur.next            # cur 指向尾节点            if cur.item == item:                # 尾部删除                pre.next = cur.next    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

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