Find the Sum of Array Elements at Non-Prime Index in Java

The following program demonstrates how to Find the Sum of Array Elements at Non-Prime Index in Java.

Basically, a prime number is the one that is divided by only 1 or itself. So, if an array has elements at the index values 0,1,2,3,4,5,6,7,8,9,10,11,12,13 then the prime index are 2,3,5,7,11, and 13. The non-prime indexes are 0, 1, 4, 6, 8,9, 10, and 12. So in this program, first we find whether the current index is prime or non-prime. If it is non-prime, then we include the corresponding element in the sum.

class NonPrimeIndex
{
	public static void main(String[] args)
	{  //3 1 23 11 56 3 1 6 56 34 44
		int[] arr={3,1,7,8,23,45,11,90,56,3,1,89,6,33,56,34,44,98};
		System.out.println(findNonPrimeIndexSum(arr));
	}
	public static int findNonPrimeIndexSum(int[] arr)
	{
		int psum=0;
		int n=arr.length;
		for(int i=0;i<n;i++)
		{
			if(i==0 || i==1) 
				psum+=arr[i];
			else
			{
			   if(!isPrime(i))
			   {
				System.out.println(i+"  "+arr[i]);
				psum+=arr[i];
			   }
			}
		}
		return psum;
	}
	public static boolean isPrime(int n)
	{
		boolean prime=true;
		for(int i=2;i<=n/2;i++)
		{
			if(n%i==0)
			{
				prime=false;
				break;
			}
		}	
		return prime;
	}
}

Output

**A Program to Find the Sum of Array Elements at Non-Prime Index in Java**

Further Reading