This example assumes you have people who must sign up for a limited number of appointment slots. Each person is allowed to select first, second, and third choices. The program assigns people to appointments in a "stable" way where "stable" means no two people would be willing to trade appointments.
The Person class represents a person and his or her preferences.
The following code performs the assignment. It reads preference information from a text box and builds the Person objects.
Next the code makes initial assignments. For each preference level (in this example, people rank three choices 0, 1, or 2), the code examines the Person objects. If a Person is not yet assigned and that Person's preference for this level has not been assigned, the program makes that assignment.
For example, suppose the program is looking at preference 1 (the second choice). Sally has not been assigned an appointment yet and her choice number 1 is appointment slot 6. If that slot is not already taken by another Person, the program assigns it to Sally.
After it has made these preferential assignments, the program assigns any unassigned Person to any available appointment.
Next the program enters a loop looking for improvements. For each pair of Persons, the program determines whether those persons should trade appointments. For example, suppose Bill was assigned his first choice appointment number 3 and Cindy was assigned appointment number 7, which she did not list as one of her choices. Suppose Bill listed appointment 7 as his third choice and Cindy listed appointment 3 as her second choice. In this case, the program swaps Bill's and Cindy's appointments. It prefers the third/second choices over the first/none choices.