#6Airline Ticket Reselling: Fare Opportunity Planning

You are analyzing airline ticket prices over a sequence of days. fares[i] represents the market price of an airline ticket on day i. You may perform at most two buy-and-resell transactions to maximize your total gain. Each transaction consists of: Purchasing a ticket at a lower fare.; Reselling it on a later day at a higher fare.;

You must complete the first transaction before starting the second one. You cannot hold multiple tickets at the same time. You may choose to make: No transaction, one transaction, two transactions

Return the maximum total gain that can be obtained. If no profitable transaction is possible, return 0.

Real-World Applications: Airline Fare Trading; Travel Price Optimization; Market Profit Management;