public static int[] HeapSort(int[] tab){

        buildMaxHeap(tab);

        return tab;
    }

    private static void buildMaxHeap(int[] tab)
    {
        int current_last = tab.length-1;

        for(int i=tab.length-1; i >= 0; i--)
        {
            heapify(tab, 0, i);

            int x = tab[current_last];
            tab[current_last] = tab[0];
            tab[0] = x;

            current_last --;
        }
    }
    private static void heapify(int[] tab, int index, int maxIndex)
    {
        int indexOfBigger = 2 * index + 1;
        int indexOfSmaller = 2 * index + 2;


        if(indexOfBigger < maxIndex) heapify(tab, indexOfBigger, maxIndex);

        if(indexOfBigger < maxIndex && tab[index] < tab[indexOfBigger])
        {
            int x = tab[indexOfBigger];
            tab[indexOfBigger] = tab[index];
            tab[index] = x;
        }

        if(indexOfSmaller < maxIndex && tab[index] < tab[indexOfSmaller])
        {
            int x = tab[indexOfSmaller];
            tab[indexOfSmaller] = tab[index];
            tab[index] = x;
        }
    }