bool check_heap(int* heap, unsigned n)
{
    for (unsigned i = 0; i <= (n - 2) / 2; ++i)
    {
        if (heap[2 * i + 1] > heap[i])
            return false;
        if (2 * i + 2 < n && heap[2 * i + 2] > heap[i])
            return false;
    }
    return true;
}