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：

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)

反思

对于队列的使用。