SPFA，SLF优化

if (dis[xx][yy]<dis[d[head+1][1]][d[head+1][2]])
                                {
                                    t1=d[tail][1];
                                    d[tail][1]=d[head+1][1];
                                    d[head+1][1]=t1;
                                    t1=d[tail][2];
                                    d[tail][2]=d[head+1][2];
                                    d[head+1][2]=t1;
                                }