Well, it should be very difficult to buy a hard-sleeper ticket just one day in advance, and you couldn't buy it in Huangshan. You know, there is only one train from Hefei to Harbin, so it is suggested that you fly to Harbin from Hefei. It is very easy to book an air ticket online in advance.

Me again, forgotten to tell you that the train tickets are required urgently in China in early July, because it is just the beginning of Chinese students' summer holiday.

Thanks for you answer