346. Moving Average from Data Stream

346. Moving Average from Data Stream
//I’m not familiar with initializing instance var and use them under constructor 



class MovingAverage {

    /** Initialize your data structure here. */
    private int maxSize;     // use private? Why 
    private double sum = 0.0; // here uses double
    private Queue<Integer> queue;
    
    public MovingAverage(int size) {
      queue = new LinkedList<Integer>();
      maxSize = size;
        
    }
    
    public double next(int val) {
    // returns the average so far 
    if(queue.size() == maxSize){ 
        sum = sum - queue.poll();
      }
      queue.offer(val);
      sum += val;
      double average = sum / queue.size();
      return average;
        
        
    }
}

 

the next() func takes in an integer, 

First check if the queue size() == maxSize

if it’s the same, then we poll the top, which is the one we added first .update the sum , sum - queue.poll()

 

And offer the new one from the bottom , update the sum , sum + queue.poll()

 

And calculate the average 

 

If it’s not the same, then we can just offer the new element and update the same 

 

 

 

 

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

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