Hash table - Wikipedia, the free encyclopedia
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Saved by 12 people (-6 private), first by anonymouse user on 2006-07-13
- Siznax on 2009-03-05 - Tags comp.sci
- Leapclif on 2009-02-06 - Tags hash
- Anirudh_22 on 2008-11-09 - Tags no_tag
- Glasswort on 2008-10-24 - Tags no_tag
- Mrsinguyen on 2008-06-09 - Tags hash , programming , algorithm , data-structure , algorithms
Public Sticky notes
H
ash tables support the efficient insertion of new entries, expecte
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hash table; both i
nsertion and search approac
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Evaluating a good hash function can be a slow operation. In particular, if simple array indexing can be used instead, this is usually faster.
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Hash tables in general exhibit poor locality of reference
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Compared to other associative array data structures, hash tables are most useful when large numbers of records are to be stored, especially if the size of the data set can be predicted.
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a black hat with knowledge of the hash function may be able to supply information to a hash which creates worst-case behavior by causing excessive collisions, resulting in very poor performance (i.e., a denial of service attack)
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he primary operation it supports efficiently is a lookup: given a key (e.g. a person's name), find the corresponding value (e.g. that person's telephone number). It works by transforming the key using a hash function into a hash, a number that is used as an index in an array to locate the desired location ("bucket") where the values should be.
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The primary operation it supports efficiently is a lookup:
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Simple Uniformed Hashing Assumption
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With a good hash function, a hash table can typically contain about 70%–80% as many elements as it does table slots and still perform well.
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1 + 2 + 4 + 8 + ... + n = 2n - 1.
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