# -*- coding:utf-8 -*-
#! python3
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()