346. Moving Average from Data Stream
[https://leetcode.com/problems/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.
For example,
MovingAverage m = new MovingAverage(3);
m.next(1) = 1
m.next(10) = (1 + 10) / 2
m.next(