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

Example:

MovingAverage m = new MovingAverage(3);
m.next(1) = 1
m.next(10) = (1 + 10) / 2
m.next(3) = (1 + 10 + 3) / 3
m.next(5) = (10 + 3 + 5) / 3

维护一个队列，保持size不大于设置的size值，队列size达到这个值得时候，去掉最早的数字，更新队列中数字的总和

class MovingAverage {
    private LinkedList<Integer> queue;
    private int sum;
    private int size;

    /** Initialize your data structure here. */
    public MovingAverage(int size) {
        this.queue = new LinkedList<Integer>();
        this.size = size;
    }

    public double next(int val) {
        this.queue.offer(val);
        sum += val;

        if(this.queue.size() == size + 1) {
            sum -= this.queue.poll();
        }

        return sum * 1.0 / this.queue.size();
    }
}

/**
 * Your MovingAverage object will be instantiated and called as such:
 * MovingAverage obj = new MovingAverage(size);
 * double param_1 = obj.next(val);
 */