## Tuesday, May 6, 2014

### Problem

Given a stream of numbers, print average (or mean) of the stream at every point.

### Example

For example, let us consider the stream as 10, 20, 30, 40, 50, 60, …
```  Average of 1 numbers is 10.00
Average of 2 numbers is 15.00
Average of 3 numbers is 20.00
Average of 4 numbers is 25.00
Average of 5 numbers is 30.00
Average of 6 numbers is 35.00
..................
```

### Solution

To print mean of a stream, we need to find out how to find average when a new number is being added to the stream. To do this, all we need is count of numbers seen so far in the stream, previous average and new number. Let n be the count, prev_avg be the previous average and x be the new number being added. The average after including x number can be written as (prev_avg*n + x)/(n+1).

```float getAvg(float prev_avg, int x, int n)
{
return (prev_avg*n + x)/(n+1);
}

// Prints average of a stream of numbers
void streamAvg(float arr[], int n)
{
float avg = 0;
for(int i = 0; i < n; i++)
{
avg  = getAvg(avg, arr[i], i);
out.println("Average of "+String.valueOf(i+1)+" numbers is "+avg);
}
return;
}
```

References