recursively sum the integers in an array

Question

I have a program that I\'m trying to make for class that returns the sum of all the integers in an array using recursion. Here is my program thus far:

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Answer 1

This is the one recursive solution with complexity O(N).and with input parameter A[] only.
You can handle null and empty(0 length) case specifically as Its returning 0 in this solution. You throw Exception as well in this case.

---

/*
 * Complexity is O(N)
 */
public int recursiveSum2(int A[])
{
    if(A == null || A.length==0)
    {
        return 0;
    }
    else
    {
        return recursiveSum2Internal(A,A.length-1);
    }
}
private int recursiveSum2Internal(int A[],int length)
{
    if(length ==0 )
    {
        return A[length];
    }
    else
    {
        return A[length]+recursiveSum2Internal(A, length-1);
    }
}

Answer 2

Try this if you don't want to pass the length of the array :

private static int sumOfArray(int[] array) {

        if (1 == array.length) {
            return array[array.length - 1];
        }

        return array[0] + sumOfArray(Arrays.copyOfRange(array, 1, array.length));
    }

Offcourse you need to check if the array is empty or not.

Answer 3

The issue is that a[n-1] is an int, whereas sumOfArray expects an array of int.

Hint: you can simplify things by making sumOfArray take the array and the starting (or ending) index.