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In computer science, a perfect hash functionh for a set S is a hash function that maps distinct elements in S to a set of m integers, with no collisions. In mathematical terms, it is an injective function.
Perfect hash functions may be used to implement a lookup table with constant worst-case access time. A perfect hash function can, as any hash function, be used to implement hash tables, with the advantage that no collision resolution has to be implemented. In addition, if the keys are not in the data and if it is known that queried keys will be valid, then the keys do not need to be stored in the lookup table, saving space.
Disadvantages of perfect hash functions are that S needs to be known for the construction of the perfect hash function. Non-dynamic perfect hash functions need to be re-constructed if S changes. For frequently changing S dynamic perfect hash functions may be used at the cost of additional space.[1] The space requirement to store the perfect hash function is in O(n) where n is the number of keys in the structure.
The important performance parameters for perfect hash functions are the evaluation time, which should be constant, the construction time, and the representation size.
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In computer science, a perfecthashfunction h for a set S is a hashfunction that maps distinct elements in S to a set of m integers, with no collisions...
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data type that maps keys to values. A hash table uses a hashfunction to compute an index, also called a hash code, into an array of buckets or slots...
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squares (~bits in the corresponding hashfunction). As with other schemes which require a perfecthashingfunction, an exhaustive process of enumeration...
perfecthashfunction, and can be implemented using as few as O ( m log log log n ) {\displaystyle O(m\log \log \log n)} bits. A succinct hash table...
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than 2n{\displaystyle 2n}. Hashfunction Dynamic perfecthashing Daniel Roche (2013). SI486D: Randomness in Computing, Hashing Unit. United States Naval...
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duplicates of a relatively small number of items, a constant-time perfecthashfunction can greatly speed up finding where to put an item1, turning the...
system can be linked against it as well. During the chroot phase, bash's hashing feature is turned off and the temporary toolchain's bin directory moved...
cryptographic algorithms, typically block ciphers and cryptographic hashfunctions, wherein if an input is changed slightly (for example, flipping a single...
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(pigeonholes). With a birthday attack, it is possible to find a collision of a hashfunction with 50 % {\textstyle 50\%} chance in 2 n = 2 n / 2 {\textstyle {\sqrt...
Hopscotch hashing is a scheme in computer programming for resolving hash collisions of values of hashfunctions in a table using open addressing. It is...
a cryptographic hashfunction is computed, and only the resulting hash is digitally signed. Cryptographic hashfunctions are functions that take a variable-length...
x\in X} to values y = h ( x ) ∈ Y {\displaystyle y=h(x)\in Y} using a hashfunction h {\displaystyle h} , and then test for membership of x ′ ∈ X {\displaystyle...
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