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"""

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])