helper

struct Queue{

    BST * data;
    Queue * next;

};

int isEmpty(Queue * last)
{
    if(last == NULL)
        return 1;
    else
        return 0;
}

Queue * enqueue(Queue * last, BST * value)
{
    Queue * temp = (Queue*)(malloc(sizeof(Queue)));
    temp->data = value;

    if(isEmpty(last))
    {
        temp->next = temp;
        last = temp;
    }
    else
    {
        temp->next = last->next;
        last->next = temp;
        last = temp;
    }
    return last;
}

Queue * dequeue(Queue * last)
{
    if((last == NULL) || (last->next == last))
    {
        return NULL;
    }
    last->next  = last->next->next;
    return last;
}

BST * top(Queue * last)
{
    if(isEmpty(last))
        return NULL;
    else
        return last->next->data;
}