A set is an efficient data structure for storing and processing nonduplicate elements. A map is like a dictionary that provides a quick lookup to retrieve a value using a key.

The “No-Fly” list is a list, created and maintained by the U.S. government’s Terrorist Screening Center, of people who are not permitted to board a commercial aircraft for travel in or out of the United States. Suppose we need to write a program that checks whether a person is on the No-Fly list. You can use a list to store names in the No-Fly list. However, a more efficient data structure for this application is a set.

Suppose your program also needs to store detailed information about terrorists in the No-Fly list. The detailed information such as gender, height, weight, and nationality can be retrieved using the name as the key. A map is an efficient data structure for such a task.