# 列表实现队列
class listQueue(object):
  def __init__(self):
    self.items = []

  def is_empty(self):
    return self.items == None

  def size(self):
    return len(self.items)

  # 入队
  def enqueue(self, value):
    return self.items.append(value)

  # 出队
  def dequeue(self):
    if self.is_empty():
      raise Exception("queue is empty !")
    return self.items.pop(0)

# 链表实现队列
class linkedQueue(object):
  class Node(object):
    def __init__(self, value=None):
      self.value = value
      self.next = None

  def __init__(self):
    self.head = None
    self.tail = None
    #self.head.next = self.tail
    self.length = 0

  def is_empty(self):
    return self.length == 0

  def size(self):
    return self.length

  def enqueue(self, value):
    node = self.Node(value)
    if self.is_empty():
      self.head = node
    else:
      self.tail.next = node
    self.tail = node
    self.length += 1

  def dequeue(self):
    if self.is_empty():
      raise Exception("queue is empty !")
    item = self.head.value
    self.head = self.head.next
    self.length -= 1
    print("出队列元素为：",item)
    return item

link = linkedQueue()
link.enqueue(1)
link.enqueue(2)
link.enqueue(3)
link.enqueue(4)
print("队列长度为：",link.size())
link.dequeue()
link.dequeue()