void Heap::repairDown(int index){
    int leftChildIndex = 2 * index + 1;
    int rightChildIndex = 2 * index + 2;

    if (leftChildIndex >= total) // koniec drzewa. Parametr index opisuje liść
        return;

    int minIndex = index;

    if (data[index] < data[leftChildIndex])
    {
        minIndex = leftChildIndex;
    }

    if ((rightChildIndex < total) && (data[minIndex] < data[rightChildIndex]))
    {
        minIndex = rightChildIndex;
    }

    if (minIndex != index)
    {
        swap(minIndex, index);
        repairDown(minIndex);
    }
}