Сортировка - Heap Sort

// Процедура просеивания пирамиды
void Sift(int *arr, int start, int length)
{
    int id_left, id_right, max, t, i = start;
    char flag = 1;

    while ((i < length) && flag)
    {
        if (2 * i + 1 < length)
        {
            if (2 * i + 1 == length - 1)
            {
                max = 2 * i + 1;
            }
            else
            {
                id_left = 2 * i + 1;
                id_right = (i + 1) * 2;
                max = (arr[id_left] >= arr[id_right]) ? id_left : id_right;
            }

            if (arr[i] <= arr[max])
            {
                t = arr[i];
                arr[i] = arr[max];
                arr[max] = t;
            }

            i = max;
        }
        else
            flag = 0;
    }
}


// Процедура пирамидальной сортировки
void HeapSort(int *arr, int length)
{
    for (int i = length / 2; i >= 0; i--)
    {
        Sift(arr, i, length);
    }

    while (length > 0)
    {
        int t = arr[length - 1];
        arr[length - 1] = arr[0];
        arr[0] = t;
        length--;

        Sift(arr, 0, length);
    }
}