Question

剑指 Offer II 041. 滑动窗口的平均值

题目描述

给定一个整数数据流和一个窗口大小，根据该滑动窗口的大小，计算滑动窗口里所有数字的平均值。

实现 MovingAverage 类：

• MovingAverage(int size) 用窗口大小 size 初始化对象。
• double next(int val) 成员函数 next 每次调用的时候都会往滑动窗口增加一个整数，请计算并返回数据流中最后 size 个值的移动平均值，即滑动窗口里所有数字的平均值。

 

示例：

输入：
inputs = ["MovingAverage", "next", "next", "next", "next"]
inputs = [[3], [1], [10], [3], [5]]
输出：
[null, 1.0, 5.5, 4.66667, 6.0]

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

 

提示：

• 1 <= size <= 1000
• -105 <= val <= 105
• 最多调用 next 方法 104 次

 

注意：本题与主站 346 题相同： https://leetcode.cn/problems/moving-average-from-data-stream/

解法

方法一：循环数组

class MovingAverage:
  def __init__(self, size: int):
    self.arr = [0] * size
    self.s = 0
    self.cnt = 0

  def next(self, val: int) -> float:
    idx = self.cnt % len(self.arr)
    self.s += val - self.arr[idx]
    self.arr[idx] = val
    self.cnt += 1
    return self.s / min(self.cnt, len(self.arr))


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

class MovingAverage {
  private int[] arr;
  private int s;
  private int cnt;

  public MovingAverage(int size) {
    arr = new int[size];
  }

  public double next(int val) {
    int idx = cnt % arr.length;
    s += val - arr[idx];
    arr[idx] = val;
    ++cnt;
    return s * 1.0 / Math.min(cnt, arr.length);
  }
}

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

class MovingAverage {
public:
  MovingAverage(int size) {
    arr.resize(size);
  }

  double next(int val) {
    int idx = cnt % arr.size();
    s += val - arr[idx];
    arr[idx] = val;
    ++cnt;
    return (double) s / min(cnt, (int) arr.size());
  }

private:
  vector<int> arr;
  int cnt = 0;
  int s = 0;
};

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

type MovingAverage struct {
  arr []int
  cnt int
  s   int
}

func Constructor(size int) MovingAverage {
  arr := make([]int, size)
  return MovingAverage{arr, 0, 0}
}

func (this *MovingAverage) Next(val int) float64 {
  idx := this.cnt % len(this.arr)
  this.s += val - this.arr[idx]
  this.arr[idx] = val
  this.cnt++
  return float64(this.s) / float64(min(this.cnt, len(this.arr)))
}

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

方法二：队列

class MovingAverage:
  def __init__(self, size: int):
    self.n = size
    self.s = 0
    self.q = deque()

  def next(self, val: int) -> float:
    if len(self.q) == self.n:
      self.s -= self.q.popleft()
    self.q.append(val)
    self.s += val
    return self.s / len(self.q)


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

class MovingAverage {
  private Deque<Integer> q = new ArrayDeque<>();
  private int n;
  private int s;

  public MovingAverage(int size) {
    n = size;
  }

  public double next(int val) {
    if (q.size() == n) {
      s -= q.pollFirst();
    }
    q.offer(val);
    s += val;
    return s * 1.0 / q.size();
  }
}

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

class MovingAverage {
public:
  MovingAverage(int size) {
    n = size;
  }

  double next(int val) {
    if (q.size() == n) {
      s -= q.front();
      q.pop();
    }
    q.push(val);
    s += val;
    return (double) s / q.size();
  }

private:
  queue<int> q;
  int s = 0;
  int n;
};

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

type MovingAverage struct {
  q []int
  s int
  n int
}

func Constructor(size int) MovingAverage {
  return MovingAverage{n: size}
}

func (this *MovingAverage) Next(val int) float64 {
  if len(this.q) == this.n {
    this.s -= this.q[0]
    this.q = this.q[1:]
  }
  this.q = append(this.q, val)
  this.s += val
  return float64(this.s) / float64(len(this.q))
}

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