In computer science, a search algorithm is any algorithm which solves the Search problem, namely, to retrieve information stored within some data structure, or calculated in the search space of a problem domain. Examples of such structures include but are not limited to a Linked List, an Array data structure, or a Search tree. The appropriate search algorithm often depends on the data structure being searched, and may also include prior knowledge about the data. Searching also encompasses algorithms that query the data structure, such as the SQL SELECT command.[1][2]

Search algorithms can be classified based on their mechanism of searching. Linear search algorithms check every record for the one associated with a target key in a linear fashion.[3][4] Binary, or half interval searches, repeatedly target the center of the search structure and divide the search space in half. Comparison search algorithms improve on linear searching by successively eliminating records based on comparisons of the keys until the target record is found, and can be applied on data structures with a defined order.[4] Digital search algorithms work based on the properties of digits in data structures that use numerical keys.[5] Finally, hashing directly maps keys to records based on a hash function.[6] Searches outside a linear search require that the data be sorted in some way.

Search functions are also evaluated on the basis of their complexity, or maximum theoretical run time. Binary search functions, for example, have a maximum complexity of `O(log n)`, or logarithmic time. This means that the maximum number of operations needed to find the search target is a logarithmic function of the size of the search space.

(information from wikipedia)

### References

1. Beame & Fich 2002, p. 39.
2. Knuth 1998, §6.5 ("Retrieval on Secondary Keys").
3. Knuth 1998, §6.1 ("Sequential Searching").
4. Knuth 1998, §6.2 ("Searching by Comparison of Keys").
5. Knuth 1998, §6.3 (Digital Searching).
6. Knuth 1998, §6.4, (Hashing).