python 用數組實現隊列

# 數組有一個固定的長度。頭指針和尾指針，都指向數組第一個值。
# 當進行push操作的時候，頭指針后移。當進行pop操作的時候，尾指針向后移
# 當到達最后一個值的時候，重新指向第一個值。取模 %queue_size()



# 首先實現一個數組

class Array(object):
    def __init__(self,size = 32):
        self._size = size
        self._items = [None] * size  # 容器_items, 是一個每個值為None的列表


    def __getitem__(self, index):      # 實現下標訪問
        return self._items[index]


    def __setitem__(self, index, value):
        self._items[index] = value


    def __len__(self):
        return self._size


    def clear(self, value=None):
        for i in range(len(self._items)):
            self._items[i] = value


    def __iter__(self):
        for item in self._items:
            yield item



class ArrayQueue(object):
    def __init__(self, maxsize):
        self.maxsize = maxsize
        self.array = Array(maxsize)
        self.head = 0
        self.tail = 0


    def push(self, value):
        if len(self) >= self.maxsize:
            raise Exception('queue full')

        self.array[self.head % self.maxsize] = value
        self.head += 1


    def pop(self):
        value = self.array[self.tail % self.maxsize]
        self.tail += 1
        return value


    def __len__(self):
        return self.head - self.tail









def test_arrrayqueue():

    import pytest
    size = 5
    q = ArrayQueue(size)
    for i in range(size):
        q.push(i)

    assert len(q) == size


    assert q.pop() == 0


    assert q.pop() == 1
    q.push(5)
    assert len(q) == 4
    assert q.pop() == 2
    assert q.pop() == 3
    assert q.pop() == 4
    assert q.pop() == 5

    assert len(q) == 0