old_contents: """
      Queue based upon array
      用数组实现的队列
  
      Author: Wenru
  """
  
  from typing import Optional
  
  class ArrayQueue:
      
      def __init__(self, capacity: int):
          self._items = []
          self._capacity = capacity
          self._head = 0
          self._tail = 0
  
      def enqueue(self, item: str) -> bool:
          if self._tail == self._capacity:
              if self._head == 0:
                  return False
              else:
                  for i in range(0, self._tail - self._head):
  <<<<<<< HEAD
                      self._data[i] = self._items[i + self._head]
  =======
                      self._items[i] = self._items[i + self._head]
  >>>>>>> upstream/master
                  self._tail = self._tail - self._head
                  self._head = 0
          
          self._items.insert(self._tail, item)
          self._tail += 1
          return True
      
      def dequeue(self) -> Optional[str]:
          if self._head != self._tail:
              item = self._items[self._head]
              self._head += 1
              return item
      
      def __repr__(self) -> str:
          return " ".join(item for item in self._items[self._head : self._tail])
  
  
new_contents: """
      Queue based upon array
      用数组实现的队列
  
      Author: Wenru
  """
  
  from typing import Optional
  
  class ArrayQueue:
      
      def __init__(self, capacity: int):
          self._items = []
          self._capacity = capacity
          self._head = 0
          self._tail = 0
  
      def enqueue(self, item: str) -> bool:
          if self._tail == self._capacity:
              if self._head == 0:
                  return False
              else:
                  for i in range(0, self._tail - self._head):
                      self._items[i] = self._items[i + self._head]
                  self._tail = self._tail - self._head
                  self._head = 0
          
          self._items.insert(self._tail, item)
          self._tail += 1
          return True
      
      def dequeue(self) -> Optional[str]:
          if self._head != self._tail:
              item = self._items[self._head]
              self._head += 1
              return item
          else:
              return None
      
      def __repr__(self) -> str:
          return " ".join(item for item in self._items[self._head : self._tail])
  
  
subject: remove wrong code, add dequene() return