346. Moving Average from Data Stream

deque 移动窗口

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

Implement the MovingAverage class:

• MovingAverage(int size) Initializes the object with the size of the window size.

• double next(int val) Returns the moving average of the last size values of the stream.

Example 1:

Input
["MovingAverage", "next", "next", "next", "next"]
[[3], [1], [10], [3], [5]]
Output
[null, 1.0, 5.5, 4.66667, 6.0]

Explanation
MovingAverage movingAverage = new MovingAverage(3);
movingAverage.next(1); // return 1.0 = 1 / 1
movingAverage.next(10); // return 5.5 = (1 + 10) / 2
movingAverage.next(3); // return 4.66667 = (1 + 10 + 3) / 3
movingAverage.next(5); // return 6.0 = (10 + 3 + 5) / 3

Constraints:

• 1 <= size <= 1000

• -105 <= val <= 105

• At most 104 calls will be made to next.

分析

dequeue(maxlen=size)自动维护窗口 无需额外弹出

from collections import deque


class MovingAverage:

    def __init__(self, size: int):
        self.size = size
        self.window = deque(maxlen=size)
        self.sum = 0

    def next(self, val: int) -> float:
        if len(self.window) < self.size:
            self.sum += val
            self.window.append(val)
            return float(self.sum / len(self.window))
        else:
            if len(self.window) == self.size:
                self.sum -= self.window[0]
            self.sum += val
            self.window.append(val)
            return float(self.sum / self.size)




# Your MovingAverage object will be instantiated and called as such:
# obj = MovingAverage(size)
# param_1 = obj.next(val)