Hashtabulky

Hashtabulky, commonly known as hash tables, are a data structure that stores associations between keys and values. They map a key to an index in an array using a hash function, and the corresponding value is stored at that bucket. The primary advantage is fast average‑case performance for insertions, lookups, and deletions, typically constant time, given a good hash function and a moderate load factor.

Collisions occur when two different keys hash to the same bucket. They are resolved mainly by separate chaining, where each bucket holds a list of entries, or by open addressing, where the algorithm probes other buckets according to a rule (linear, quadratic, or double hashing) until an empty slot is found.

Core operations include insert, search, and delete. Performance depends on the load factor and the quality of the hash function, with average‑case time near O(1) and worst‑case time approaching O(n) in degenerate scenarios.

Design considerations include choosing a robust hash function, selecting a suitable maximum load factor, and resizing (rehashing) the table as it grows. Memory usage involves storing keys and values, plus overhead for the bucket structure and any collision resolution method.

Common uses encompass dictionaries in programming languages, caches, symbol tables in compilers, and database indexing. Hash tables are valued for their simplicity and efficiency, especially when fast access to unsorted data is required.

History notes: Hashing concepts emerged in the mid‑20th century, with hash tables becoming a widely adopted tool across languages and systems, forming a standard approach to associative storage.