What concept underlies the HashSet data structure?

The data structure HashSet is based on the concept of a hash table. It provides storage for unique elements with fast access, addition, and removal.

Main points:

• Each element is transformed into a hash code using a hash function.
• The hash code is used to determine the position (bucket) in the internal array.
• In case of collisions (when different elements have the same hash), collision resolution methods are used (e.g., chaining or open addressing).
• HashSet guarantees that each element is stored only once (uniqueness).

This allows operations like checking for the presence of an element, adding, and removing to be performed in amortized time close to O(1).

Example of usage in Java:

import java.util.HashSet;

HashSet<String> set = new HashSet<>();
set.add("apple");
set.add("banana");
set.add("apple"); // will not be added a second time

System.out.println(set.contains("banana")); // true
System.out.println(set.size()); // 2

Thus, HashSet is a set implemented based on a hash table for efficient storage of unique elements.