How is the HashMap data structure implemented and what is it based on?

HashMap is a data structure that stores key-value pairs and provides quick access to values by key.

The main principle of HashMap operation is based on using a hash function, which transforms the key into an array index (bucket). This index indicates where the corresponding value is stored in memory.

If multiple keys have the same hash (collision), a list or tree of elements is stored in one bucket, where the search by key occurs.

A simplified logic example:

• When adding a key-value pair, the hash of the key is calculated.
• The bucket is determined by the hash.
• If the bucket is empty, the element is added there.
• If the bucket is occupied, a search is performed through the list/tree to update or add the element.

This provides an average access complexity of O(1), but in the worst case (many collisions), it can be O(n).