void Dijkstra(City** Cities, City* start)
{
    int previous[20] = { -1 };
    double distances[20] = { DBL_MAX };
    distances[start->citynum] = 0;
    PQHead* QHead = (PQHead*)calloc(1, sizeof(PQHead));
    PQPush(start, QHead, 0);
    while (!PQIsEmpty(QHead))
    {
        City* u = PQTop(QHead);
        Con * p = u->Head->pHead;
        while (p)
        {
            if (distances[p->cityB] > distances[u->citynum] + p->dist)
            {
                distances[p->cityB] = distances[u->citynum] + p->dist;
                previous[p->cityB] = u->citynum;
                PQPush(Cities[p->cityB - 1], QHead, p->dist);
            }
            p = p->next;
        }
    }
}