Question

346. Moving Average from Data Stream

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Description

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.

Solutions

Solution 1

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);
 */

Solution 2

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);
 */