## Cuckoo hashing

Cuckoo hashing is a scheme in computer programming for resolving hash collisions of values of hash functions in a table. Cuckoo hashing was first described by Rasmus Pagh and Flemming Friche Rodler in 2001. The name derives from the behavior of some species of cuckoo, where the cuckoo chick pushes the other eggs or young out of the nest when it hatches.

### Theory

The basic idea is to use two hash functions instead of only one. This provides two possible locations in the hash table for each key.

When a new key is inserted, a greedy algorithm is used: The new key is inserted in one of its two possible locations, “kicking out”, that is, displacing, any key that might already reside in this location. This displaced key is then inserted in its alternative location, again kicking out any key that might reside there, until a vacant position is found, or the procedure enters an infinite loop. In the latter case, the hash table is rebuilt in-place using new hash functions.