smile.hash

Class PerfectHash

java.lang.Object

smile.hash.PerfectHash

All Implemented Interfaces:

java.io.Serializable

public class PerfectHash
extends java.lang.Object
implements java.io.Serializable

A perfect hash of an array of strings to their index in the array.

A perfect hash function for a set S is a hash function that maps distinct elements in S to a set of 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 for a specific set S can be found by a randomized algorithm in a number of operations that is proportional to the size of S. The original construction of Fredman, Komlós and Szemerédi (1984) chooses a large prime p (larger than the size of the universe from which S is drawn), and a parameter k, and maps each element x of S to the index g(x) = (kx mod p) mod n.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
PerfectHash(int[] select, java.lang.String... keywords) Constructs the perfect hash of strings.
PerfectHash(java.lang.String... keywords) Constructs the perfect hash of strings.

Method Summary

Modifier and Type	Method and Description
int	get(java.lang.String key) Returns the index of a string.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PerfectHash

public PerfectHash(java.lang.String... keywords)

Constructs the perfect hash of strings.

PerfectHash

public PerfectHash(int[] select,
                   java.lang.String... keywords)

Constructs the perfect hash of strings.

Parameters:

select - The character positions in keywords used to calculate the hash.

Method Detail

get

public int get(java.lang.String key)

Returns the index of a string. If the string is in the set, returns its array index. Otherwise, -1.