346. Moving Average from Data Stream π ο
Descriptionο
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 windowsize.double next(int val)Returns the moving average of the lastsizevalues 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
104calls will be made tonext.
Solutionsο
Solution 1: Circular Arrayο
We define a variable $\textit{s}$ to calculate the sum of the last $\textit{size}$ elements, and a variable $\textit{cnt}$ to record the total number of current elements. Additionally, we use an array $\textit{data}$ of length $\textit{size}$ to record the value of each element at each position.
When calling the $\textit{next}$ function, we first calculate the index $i$ where $\textit{val}$ should be stored, then update the sum $s$, set the value at index $i$ to $\textit{val}$, and increment the element count by one. Finally, we return the value of $\frac{s}{\min(\textit{cnt}, \textit{size})}$.
The time complexity is $O(1)$, and the space complexity is $O(n)$, where $n$ is the integer $\textit{size}$ given in the problem.
Python3ο
class MovingAverage:
def __init__(self, size: int):
self.s = 0
self.data = [0] * size
self.cnt = 0
def next(self, val: int) -> float:
i = self.cnt % len(self.data)
self.s += val - self.data[i]
self.data[i] = val
self.cnt += 1
return self.s / min(self.cnt, len(self.data))
# Your MovingAverage object will be instantiated and called as such:
# obj = MovingAverage(size)
# param_1 = obj.next(val)
Javaο
class MovingAverage {
private int s;
private int cnt;
private int[] data;
public MovingAverage(int size) {
data = new int[size];
}
public double next(int val) {
int i = cnt % data.length;
s += val - data[i];
data[i] = val;
++cnt;
return s * 1.0 / Math.min(cnt, data.length);
}
}
/**
* Your MovingAverage object will be instantiated and called as such:
* MovingAverage obj = new MovingAverage(size);
* double param_1 = obj.next(val);
*/
C++ο
class MovingAverage {
public:
MovingAverage(int size) {
data.resize(size);
}
double next(int val) {
int i = cnt % data.size();
s += val - data[i];
data[i] = val;
++cnt;
return s * 1.0 / min(cnt, (int) data.size());
}
private:
int s = 0;
int cnt = 0;
vector<int> data;
};
/**
* Your MovingAverage object will be instantiated and called as such:
* MovingAverage* obj = new MovingAverage(size);
* double param_1 = obj->next(val);
*/
Goο
type MovingAverage struct {
s int
cnt int
data []int
}
func Constructor(size int) MovingAverage {
return MovingAverage{
data: make([]int, size),
}
}
func (this *MovingAverage) Next(val int) float64 {
i := this.cnt % len(this.data)
this.s += val - this.data[i]
this.data[i] = val
this.cnt++
return float64(this.s) / float64(min(this.cnt, len(this.data)))
}
/**
* Your MovingAverage object will be instantiated and called as such:
* obj := Constructor(size);
* param_1 := obj.Next(val);
*/
TypeScriptο
class MovingAverage {
private s: number = 0;
private cnt: number = 0;
private data: number[];
constructor(size: number) {
this.data = Array(size).fill(0);
}
next(val: number): number {
const i = this.cnt % this.data.length;
this.s += val - this.data[i];
this.data[i] = val;
this.cnt++;
return this.s / Math.min(this.cnt, this.data.length);
}
}
/**
* Your MovingAverage object will be instantiated and called as such:
* var obj = new MovingAverage(size)
* var param_1 = obj.next(val)
*/
Solution 2: Queueο
We can use a queue $\textit{q}$ to store the last $\textit{size}$ elements, and a variable $\textit{s}$ to record the sum of these $\textit{size}$ elements.
When calling the $\textit{next}$ function, we first check if the length of the queue $\textit{q}$ is equal to $\textit{size}$. If it is, we dequeue the front element of the queue $\textit{q}$ and update the value of $\textit{s}$. Then we enqueue $\textit{val}$ and update the value of $\textit{s}$. Finally, we return the value of $\frac{s}{\text{len}(q)}$.
The time complexity is $O(1)$, and the space complexity is $O(n)$, where $n$ is the integer $\textit{size}$ given in the problem.
Python3ο
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)
Javaο
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);
*/
C++ο
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);
*/
Goο
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);
*/
TypeScriptο
class MovingAverage {
private q: number[] = [];
private s: number = 0;
private n: number;
constructor(size: number) {
this.n = size;
}
next(val: number): number {
if (this.q.length === this.n) {
this.s -= this.q.shift()!;
}
this.q.push(val);
this.s += val;
return this.s / this.q.length;
}
}
/**
* Your MovingAverage object will be instantiated and called as such:
* var obj = new MovingAverage(size)
* var param_1 = obj.next(val)
*/