Country of origin and destination

Hi, for the 72 hour free transit, can the country of origin and destination be the same or it has to be different? For example, can I fly from US/HK/Macau/Taiwan/Japan/etc. to Beijing and then leave for the same country I came from without a visa? Or do I have to come from and go to a different country?

Furthermore, can I travel on two one-way plane tickets (purchased prior to landing in China and can provide proof)? Or does the entire itinerary have to be on the same ticket number from the same airline?

Thank you very much!