MarshallCN
commented
7 years ago 
The seats_id of new tickets equals to carriage capacity - (total remaining seats number - empty carriage number carriage capacity)+1;
eg. carriage capacity=80, a train has 2 carriages which already sells 2 tickets, 158 seats is remaining,
so when new tickets sell, seat_id = 80 - (158-1*80) + 1 = 3,
but the first ticket is = 80 - (160-2\80) + 1 = 81, which is wrong