hajutustabelit

Hajutustabelid, known in English as hash tables or hash maps, are data structures that implement an associative array abstract data type. They are used to store key-value pairs. A hash table allows for efficient insertion, deletion, and retrieval of data. The core idea behind a hash table is to use a hash function to compute an index, also known as a hash code or hash value, into an array of buckets or slots. This hash code is then used to directly access the location where the value associated with the key is stored.

The efficiency of a hash table largely depends on the quality of the hash function. A good hash function distributes keys uniformly across the array, minimizing the chances of collisions. Collisions occur when two different keys produce the same hash code, meaning they map to the same bucket. Various collision resolution strategies exist, such as separate chaining (where each bucket stores a linked list of entries) or open addressing (where colliding elements are placed in other empty slots in the table).

The time complexity for basic operations like insertion, deletion, and lookup in a hash table is typically O(1) on average, assuming a good hash function and minimal collisions. However, in the worst-case scenario, where many collisions occur, the complexity can degrade to O(n), where n is the number of elements. Hash tables are widely used in various applications, including databases, caches, symbol tables in compilers, and implementing sets.