java merge

        private int[] merge(int[] arr, int lower, int upper)
        {
            if (lower == upper)
            {
                return arr;
            }
            int mid = (lower + upper) >> 1;
            merge(arr, lower, mid);
            merge(arr, mid + 1, upper);
            return mergeArrays(arr, lower, mid + 1, upper + 1);
        }

        private int[] mergeArrays(int[] arr, int lower, int mid, int upper)
        {
            int temp = mid;
            int i = 0;
            for (; lower < temp && mid < upper; )
            {
                if (arr[lower] < arr[mid])
                {
                    lower++;
                }
                else
                {
                    swap(arr, mid, lower);
                    mid++;
                }
                i++;
            }
            return arr;
        }

        private void swap(int[] arr, int i, int j)
        {
            int temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }