346. Moving Average from Data Stream

问题描述

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(3) = (1 + 10 + 3) / 3
m.next(5) = (10 + 3 + 5) / 3

题目链接：

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思路分析

滑动窗口计算平均数，限定计算size个数的平均数。

将每一次的输入保存在队列中，并保持一个sum来记录队列中元素和。如果队列中元素小于size，push进队后计算平均数，注意++n，因为元素个数增多了；如果到了size了，就先pop再push，sum做相同操作，再进行计算。

代码

class MovingAverage {
public:
    /** Initialize your data structure here. */
    queue<int> window;
    double sum = 0;
    int cap;
    MovingAverage(int size) {
        cap = size;
    }

    double next(int val) {
        int n = window.size();
        if (n < cap){
            sum = sum + val;
            window.push(val);
            return sum/(++n);
        }
        else{
            sum = sum - window.front() + val;
            window.pop();
            window.push(val);
            return sum/cap;
        }

    }
};

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

时间复杂度：$O(1)$
空间复杂度：$O(n)$

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反思

对于队列的使用。