How to find maximum of each subarray of some fixed given length in a given array

Question

We are given an array of n elements and an integer k. Suppose that we want to slide a window of length k across the array, reporting the largest value contained in each window.

Answer 1

Please review my code. According to me I think the Time Complexity for this algorithm is

O(l) + O(n)

    for (int i = 0; i< l;i++){
        oldHighest += arraylist[i];
    }
    int kr = FindMaxSumSubArray(arraylist, startIndex, lastIndex);



    public static int FindMaxSumSubArray(int[] arraylist, int startIndex, int lastIndex){

    int k = (startIndex + lastIndex)/2;
    k = k - startIndex;
    lastIndex = lastIndex  - startIndex;

    if(arraylist.length == 1){
        if(lcount= oldHighest){
                oldHighest = highestSum;
                result = count - l + 1;
            }
            highestSum = 0;
            highestSum += arraylist[0];
            lcount = 1;
        }
        count++;
        return result;
    }

    FindMaxSumSubArray(Arrays.copyOfRange(arraylist, 0, k+1), 0, k);
    FindMaxSumSubArray(Arrays.copyOfRange(arraylist, k+1, lastIndex+1), k+1, lastIndex);

    return result;
 }

I don't understand if this is better off to do in recursion or just linearly?