private sort()

/* Recursive merge sort logic */
private static void sort(int[] elements, int[] aux, int low, int high) {
    if (high <= low) {                              // 1
        return;                                     // 1
    }

    int mid = low + (high - low) / 2;               // 2
    sort(elements, aux, low, mid);                  // 3
    sort(elements, aux, mid + 1, high);             // 3
    merge(elements, aux, low, mid, high);           // 4
}