346. Moving Average from Data Stream

O(1) time O(size) space

class MovingAverage {
public:
    /** Initialize your data structure here. */
    MovingAverage(int size) : n(size), sum(0) {

    }

    double next(int val) {
        q.push(val);
        sum += val;
        if (q.size() > n) {
            sum -= q.front();
            q.pop();
        }
        return sum / q.size(); // 切记不能除n！！！因为queue里不一定有n个数
    }

    int n;
    double sum;
    queue<int> q;
};

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