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Another 3rd-party library, uthash, also creates associative arrays from C structures. A structure represents a value, and one of the structure fields serves as the key. [2] Finally, the GLib library also supports associative arrays, along with many other advanced data types and is the recommended implementation of the GNU Project. [3]
A small phone book as a hash table. In computer science, a hash table is a data structure that implements an associative array, also called a dictionary or simply map; an associative array is an abstract data type that maps keys to values. [2]
Another very simple implementation technique, usable when the keys are restricted to a narrow range, is direct addressing into an array: the value for a given key k is stored at the array cell A[k], or if there is no mapping for k then the cell stores a special sentinel value that indicates the lack of a mapping. This technique is simple and ...
A hash function uniform on the interval [0, n − 1] is n P(key) / 2 b. We can replace the division by a (possibly faster) right bit shift: n P(key) >> b. If keys are being hashed repeatedly, and the hash function is costly, then computing time can be saved by precomputing the hash codes and storing them with the keys.
A HAMT is an array mapped trie where the keys are first hashed to ensure an even distribution of keys and a constant key length. In a typical implementation of HAMT's array mapped trie, each node contains a table with some fixed number N of slots with each slot containing either a nil pointer or a pointer to another node. N is commonly 32.
Keys are unique identifiers which map to particular values, which in turn can be anything from addresses, to documents, to arbitrary data. [2] Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption.
Linear probing is a component of open addressing schemes for using a hash table to solve the dictionary problem.In the dictionary problem, a data structure should maintain a collection of key–value pairs subject to operations that insert or delete pairs from the collection or that search for the value associated with a given key.
A minimal perfect hash function F is order preserving if keys are given in some order a 1, a 2, ..., a n and for any keys a j and a k, j < k implies F(a j) < F(a k). [9] In this case, the function value is just the position of each key in the sorted ordering of all of the keys.