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:

```Input
["MovingAverage", "next", "next", "next", "next"]
[[3], [1], [10], [3], [5]]
Output
[null, 1.0, 5.5, 4.66667, 6.0]

Explanation
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
```

Constraints:

• `1 <= size <= 1000`
• `-105 <= val <= 105`
• At most `104` calls will be made to `next`.

346. Moving Average from Data Stream
``````use std::collections::VecDeque;

struct MovingAverage {
queue: VecDeque<i32>,
sum: i32,
size: usize,
}

impl MovingAverage {
fn new(size: i32) -> Self {
MovingAverage {
queue: VecDeque::new(),
sum: 0,
size: size as usize,
}
}

fn next(&mut self, val: i32) -> f64 {
self.sum += val;
self.queue.push_back(val);
if self.queue.len() > self.size {
if let Some(front) = self.queue.pop_front() {
self.sum -= front;
}
}
self.sum as f64 / self.queue.len() as f64
}
}

#[test]
fn test() {
use assert_approx_eq::assert_approx_eq;
let mut m = MovingAverage::new(3);
assert_approx_eq!(m.next(1), 1f64);
assert_approx_eq!(m.next(10), 5.5f64);
assert_approx_eq!(m.next(3), 14f64 / 3f64);
assert_approx_eq!(m.next(5), 6f64);
}
``````