Hajautustauluun

Hajautustauluun, known in English as a hash table, is a data structure that implements an associative array abstract data type. It stores key-value pairs and provides efficient methods for inserting, deleting, and searching for elements based on their keys. The core idea behind a hash table is to use a hash function to compute an index, or "hash code," from a key. This index is then used to determine where in an underlying array the corresponding value should be stored.

When a key-value pair is to be inserted, the hash function is applied to the key to get an index. The value is then placed at that index in the array. Similarly, to retrieve a value, the hash function is applied to the key, and the value is looked up at the computed index. The efficiency of these operations is largely dependent on the quality of the hash function and how well it distributes keys across the array.

A common challenge with hash tables is handling "collisions," which occur when two different keys hash to the same index. Various techniques are employed to resolve collisions, such as separate chaining (where each array index points to a linked list or another data structure containing all elements that hash to that index) or open addressing (where if an index is occupied, the algorithm probes for another available slot in the array). The choice of collision resolution strategy can significantly impact the performance of the hash table. Hash tables are widely used in computer science for implementing dictionaries, caches, and symbol tables due to their average constant-time performance for search, insertion, and deletion operations.