Finding Average of Array of integers using recursion

Question

I'm trying to find the average of integers elements in an array using recursion. I know how to do it using loops, but I have to do it by recursion for my assignment, so what I tried to do is to find the sum of elements using recursion and then divide the sum by the length of the array. I wrote this code but it gives me a wrong result:

public int findAvg(int a[], int n)
{
int sum,avg;
if(n==1)
 {

sum=a[0];
return sum;
}
else 
{
sum=a[n-1]+findAvg(a,n-1);
}

avg = sum/n;
return avg;}

---

The calling of findAvg method in main class:

public class main {

public static void main(String[] args) {
    // TODO Auto-generated method stub

    Recursive r = new Recursive ();
    int integersArr [] = {1,2,3,4,5};

    int max = r.findMax(integersArr,integersArr.length );
    int avg = r.findAvg(integersArr, integersArr.length);
    System.out.println("Maximum element = "+ max);
    System.out.println("Average value of elements = "+ avg);


 }

}

The console output:

Average value of elements = 1

Solution 1

First of all average of integers can be floating point. So make the return type of your function to float or double. Now,
If you have set of n numbers with average of x and you want to add one more number to the set (say b). New average will be ((n * x) + b) / (n + 1). Use the same trick in your code.

public float findAvg(int a[], int n)
{
    float sum,avg;
    if(n==1)
    {
        sum=a[0];
    }
    else 
    {
        // Calculate sum of n-1 numbers = (n-1) * (avg of n-1 numbers)
        // and add nth number to it ( i.e. a[n-1])
        sum= a[n-1]+ (n-1) * findAvg(a,n-1);
    }
    avg = sum/n;
    return avg;
}

Solution 2

First of all sum=a[n-1]+findAvg(a,n-1); is wrong, since if findAvg(a,n-1) returns the correct average for the first (n-1) elements, the sum should be a[n-1] + (n-1) * findAvg(a,n-1).

Second of all, you are losing precision when dividing integers in avg = sum/n; Consider using doubles.

Solution 3

public double average(int y[], int i) {
    double result;
    result = (double)y[i] / (double)y.length;
    if (i == 0)
        return result;
    else
        return result + average(y, i-1);
}

Comments

[AMH9]

Thank you I edited the sum so that the average returned each time by the recursive call is correct.