# 346. Moving Average from Data Stream

Given a stream of integers and a window size, calculate the moving average of all integers in the sliding window.

Implement the `MovingAverage` class:

* `MovingAverage(int size)` Initializes the object with the size of the window `size`.
* `double next(int val)` Returns the moving average of the last `size` values of the stream.

 

**Example 1:**

<pre><code><strong>Input
</strong>["MovingAverage", "next", "next", "next", "next"]
[[3], [1], [10], [3], [5]]
<strong>Output
</strong>[null, 1.0, 5.5, 4.66667, 6.0]

<strong>Explanation
</strong>MovingAverage movingAverage = new MovingAverage(3);
movingAverage.next(1); // return 1.0 = 1 / 1
movingAverage.next(10); // return 5.5 = (1 + 10) / 2
movingAverage.next(3); // return 4.66667 = (1 + 10 + 3) / 3
movingAverage.next(5); // return 6.0 = (10 + 3 + 5) / 3
</code></pre>

&#x20;

**Constraints:**

* `1 <= size <= 1000`
* `-10`<sup>`5`</sup>` ``<= val <= 10`<sup>`5`</sup>
* At most `10`<sup>`4`</sup> calls will be made to `next`.

分析

dequeue(maxlen=size)自动维护窗口 无需额外弹出

```
from collections import deque


class MovingAverage:

    def __init__(self, size: int):
        self.size = size
        self.window = deque(maxlen=size)
        self.sum = 0

    def next(self, val: int) -> float:
        if len(self.window) < self.size:
            self.sum += val
            self.window.append(val)
            return float(self.sum / len(self.window))
        else:
            if len(self.window) == self.size:
                self.sum -= self.window[0]
            self.sum += val
            self.window.append(val)
            return float(self.sum / self.size)




# Your MovingAverage object will be instantiated and called as such:
# obj = MovingAverage(size)
# param_1 = obj.next(val)
```