CuckooHashing

Cuckoo hashing is a technique used in computer science for managing dynamic hash tables with efficient worst-case lookup times. It was introduced by Rasmus Pagh and Flemming Friche Støvring in 2001. The core idea involves using two or more hash functions to determine potential locations for each key in the table. When inserting a new key, the method checks these locations. If a spot is already occupied, the existing key is "kicked out" (evicted) and relocated to its alternative position, following the same process, which can cascade through a series of displacements. This "kicking out" process continues until an empty slot is found or a maximum number of displacements is reached, at which point the table may need to be resized or rehashed.

Cuckoo hashing provides constant worst-case time for lookups because each key can only be in one of two locations, making searches very predictable and fast. Insertion, however, can be more complex because of potential displacements and the need for rehashing when a cycle occurs or when the table becomes too full.

The technique benefits from high space utilization and guarantees constant-time access, which makes it suitable for applications demanding predictable performance such as networking, caching, and database management. Variants of cuckoo hashing also incorporate multiple hash functions and multiple possible positions to further improve efficiency and reduce collision-related issues.

Overall, cuckoo hashing is valued for its simplicity, efficiency, and robustness in various computing environments. However, its performance heavily depends on the choice of hash functions and implementation details, particularly for maintaining low load factors to prevent excessive relocations.