class Node(object):
    """结点类"""


    def __init__(self, item):
        self.item = item
        self.next = None


class CyclesSingleLinkList():
    """单向循环链表"""


    def __init__(self, node=None):
        self.__head = node


    def is_empty(self):
        """链表是否为空
        :return 如果链表为空 返回真
        """
        return self.__head is None


    def length(self):
        """链表长度"""
        # 如果是空链表
        if self.is_empty():
            return 0
        cur = self.__head
        count = 1
        while cur.next != self.__head:
            count += 1
            cur = cur.next
        return count


    def travel(self):
        """遍历整个链表"""
        if self.is_empty():
            print("")
            return
        cur = self.__head
        while cur.next != self.__head:
            print(cur.item, end=" ")
            cur = cur.next
        # 从循环退出，cur指向的是尾结点
        print(cur.item)


    def add(self, item):
        """链表头部添加元素
        :param item: 要保存的具体数据
        """
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = node
        # 寻找尾结点
        cur = self.__head
        while cur.next != self.__head:
            cur = cur.next
        # 从循环中退出，cur指向尾结点
        node.next = self.__head
        self.__head = node
        cur.next = self.__head


    def append(self, item):
        """链表尾部添加元素"""
        node = Node(item)
        #如果列表为空，直接添加结点
        if self.is_empty():
            self.__head = node
            node.next = node
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            #退出循环的时候，cur指向尾结点
            cur.next = node
            node.next = self.__head


    def insert(self, pos, item):
        """指定位置添加元素"""
        # 在头部添加元素
        if pos <= 0:
            self.add(item)
        # 在尾部添加元素
        elif pos >= self.length():
            self.append(item)
        else:
            cur = self.__head
            count = 0
            while count < (pos - 1):
                count += 1
                cur = cur.next
            # 退出循环的时候，cur指向pos前一个位置
            # node插入到pos位置前
            node = Node(item)
            node.next = cur.next
            cur.next = node


    def remove(self,item):
        """删除结点"""
        if self.is_empty():
            return
        # 当前游标
        cur = self.__head
        # 当前游标的上一个游标
        pre = None
        while cur.next != self.__head:
            # 找到了要删除的元素
            if cur.item == item:
                # 在头部找到了元素
                if cur == self.__head:
                    # 先找到尾结点
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    # 退出循环后，rear指向尾结点
                    self.__head = cur.next
                    rear.next = self.__head
                else:
                    # 在中间位置找到了元素
                    pre.next = cur.next
                return
            # 不是要找的元素，移动游标
            pre = cur
            cur = cur.next
        # 退出循环后，cur指向尾结点
        if cur.item == item:
            # 链表只有一个节点
            if cur == self.__head:
                self.__head = None
            else:
                pre.next = self.__head


    def search(self,item):
        """查找结点是否存在"""
        if self.is_empty():
            return False
        cur = self.__head
        while cur.next != self.__head:
            if cur.item == item:
                return True
            cur = cur.next
        # 退出循环后，cur指向为尾结点
        if cur.item == item:
            return True
        return False


if __name__ == '__main__':
    ll = CyclesSingleLinkList()
    print(ll.length())
    ll.travel()


    ll.append(1)
    print(ll.length()) #1
    ll.travel() #1


    ll.add(2)
    print(ll.length()) #2
    ll.travel()#2 1


    ll.insert(1,3)
    ll.travel() #2 3 1


    ll.remove(1)
    ll.travel() #2 3