I am looking to travel from shanghai to chengdu and I would like to visit huanglong too.

Most people go to Huanglong from CD by bus and a single ride takes about 7 hours. So in the case one day is not enough. You can go to CD Xinnanmen or Chadianzi bus station to take the longd-distance bus departing from 06:30 to 08:00. The bus arrives at Chuanzhusi bus station; upon arrival, you can take another local bus to Huanglong.

You can also travel by plane. If you plan your sightseeing route and flights very well, one day may be enough. In the case, you'd better hire a car to travel between the airport and the scenic spot.