I am planning to travel by train from Chengdu South or Chengdu East station to Leshan station and back. I also plan to travel from Xian North station to Luoyang Longmen station and back. Do I need to buy these train tickets ahead of time, or can I buy them at the station, on the day I am travelling.

If I buy them online, from ctrip or similar website, can I pick the tickets up from them the Chengdu Shuangliu Airport train station, when I arrive?

Thanks!!