The Queue ADT

• enqueue(object)
• object dequeue()
• object first()
• integer len()
• boolean is_empty()

FIFO(First In First Out)

ex. 은행창구 번호표

Array-based Queue

• f index of the from element
• r index immediately past the rear element
  

Queue Operations

size(), isEmpty()

enqueue(o)

dequeue()

Queue in python

_data
_size
_front

class ArrayQueue:
	DEFAULT_CAPACITY = 10
    
    def __init__(self):
    	self._data = [None] * ArrayQueue.DEFAULT_CAPACITY
        self._size = 0
        self._front = 0
        
    def __len__(self):
    	return self._size
        
    def is_empty(self):
    	return self._size == 0
        
    def first(self):
    	if self.is_empty():
        	raise Empty('Queue is empty')
        return self._data[self._front]
    def dequeue(self):
    	if self.is_empty():
        	raise Empty('Queue is empty')
            answer = self._data[self._front]
            self._data[self._front] = None
            self._front = (self._front + 1) % len(self._data)
            self._size -= 1
            return answer
    .
    
    .
    .