Blue Skies Airlines, a new airline, offers services between any two of the following cities: Denver; Washington, DC; Los Angeles; New York City; Atlanta; and Cleveland.
When a customer calls Blue Skies to make a flight reservation, the reservation agent first asks him or her for
The desired travel dates
The departure and destination cities
The seat grade desired (first class, business class, or economy)
The reservation agent then informs the customer of all available flights that meet his or her criteria. For each flight, the flight number, departure date and time, arrival date and time, and round-trip price are communicated to the customer. If the customer finds any of the available flights acceptable, he or she may either pay for the ticket via credit card or request that the seat be held for 24 hours. (A specific seat assignment—row and seat number—isn't issued until the seat is paid for.)
A limited number of seats on each flight are earmarked as frequent flyer seats. A customer who is a frequent flyer member may reserve and "pay for" one of these seats by giving the agent his or her frequent flyer membership number. The agent then verifies that the appropriate balance is available in the customer's account before the seat can be confirmed, at which point those miles are deducted from the account.
The customer has two ticketing options: he or she may request that a conventional "paper" ticket be issued and mailed to his or her home address, or an electronic ticket (E-ticket) may instead be assigned, in which case the customer is simply informed of the E-ticket serial number by telephone. (With an E-ticket, the customer simply reports to the airport at the time of his or her departure, and presents suitable ID to a ticket agent at the gate. No paperwork is exchanged.) In either case, the reservation agent records the serial number of the (conventional or electronic) ticket issued to this customer.
The number of seats available for a given flight in each of the seat grade categories is dependent on the type of aircraft assigned to a given flight.
Assume that all flights are round-trip between two cities (no three-legged itineraries are permitted).
Disregard the complication that airlines sometimes have to switch aircraft at the last minute due to mechanical difficulties, thus disrupting the seating assignments.