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https://github.com/robrwo/algorithm-skiplist

Skiplists in Perl
https://github.com/robrwo/algorithm-skiplist

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Skiplists in Perl

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README 

        
NAME

    Algorithm::SkipList - Perl implementation of skip lists



REQUIREMENTS

    The following non-core modules are used:



      Tree::Node



INSTALLATION

    Installation can be done using the traditional Makefile.PL or the newer

    Build.PL method .



    Using Makefile.PL:



      perl Makefile.PL

      make test

      make install



    (On Windows platforms you should use nmake instead.)



    Using Build.PL (if you have Moddule::Build installed):



      perl Build.PL

      perl Build test

      perl Build install    



SYNOPSIS

      my $list = new Algorithm::SkipList();



      $list->insert( 'key1', 'value' );

      $list->insert( 'key2', 'another value' );



      $value = $list->find('key2');



      $list->delete('key1');



DESCRIPTION

    This is an implementation of skip lists in Perl.



    Skip lists are an alternative to balanced trees. They are ordered linked

    lists with random links at various *levels* that allow searches to skip

    over sections of the list, like so:



      4 +---------------------------> +----------------------> +

        |                             |                        |

      3 +------------> +------------> +-------> +-------> +--> +

        |              |              |         |         |    |

      2 +-------> +--> +-------> +--> +--> +--> +-------> +--> +

        |         |    |         |    |    |    |         |    |

      1 +--> +--> +--> +--> +--> +--> +--> +--> +--> +--> +--> +

             A    B    C    D    E    F    G    H    I    J   NIL



    A search would start at the top level: if the link to the right exceeds

    the target key, then it descends a level.



    Skip lists generally perform as well as balanced trees for searching but

    do not have the overhead with respect to reblanacing the structure. And

    on average, they use less memory than trees.



    They also use less memory than hashes, and so are appropriate for large

    collections.



KNOWN ISSUES

    Developer Release

        This is a developer release, with many changes to improve

        performance. Some of these changes may cause incompatabilities. See

        the Changes file.



        Algorithm::SkipList::PurePerl is not included with this release, and

        code which relies on it may fail.



        The documentation has largely been copied from the 1.02 release, and

        may not accurately reflect changes in this release.



    Undefined Values

        Certain methods such as the find and delete entries elsewhere in

        this document will return the the value associated with a key, or

        `undef' if the key does not exist. However, if the value is `undef',

        then these functions will appear to claim that the key cannot be

        found.



        In such circumstances, use the exists method to test for the

        existence of a key.



    Duplicate Keys

        Duplicate keys are an experimental feature in this module, since

        most methods have been designed for unique keys only.



        Access to duplicate keys is akin to a stack. When a duplicate key is

        added, it is always inserted *before* matching keys. In searches, to

        find duplicate keys one must use find_with_finger or the

        find_duplicates method.



        The copy method will reverse the order of duplicates.



        The behavior of the the merge and append entries elsewhere in this

        document methods is not defined for duplicates.



    Non-Determinism

        Skip lists are non-deterministic. Because of this, bugs in programs

        that use this module may be subtle and difficult to reproduce

        without many repeated attempts. This is especially true if there are

        bugs in a custom node.



    Additional issues may be listed on the CPAN Request Tracker at

    http://rt.cpan.org/NoAuth/Bugs.html?Dist=Algorithm-SkipList or

    http://rt.cpan.org/NoAuth/Bugs.html?Dist=List-SkipList.



AUTHOR

    Robert Rothenberg 



  Acknowledgements



    Carl Shapiro for introduction to skip lists.



  Suggestions and Bug Reporting



    Feedback is always welcome. Please use the CPAN Request Tracker at

    http://rt.cpan.org to submit bug reports.



LICENSE

    Copyright (c) 2003-2005, 2008-2010 Robert Rothenberg. All rights

    reserved. This program is free software; you can redistribute it and/or

    modify it under the same terms as Perl itself.



SEE ALSO

    See the article by William Pugh, "A Skip List Cookbook" (1989), or

    similar ones by the author at http://www.cs.umd.edu/~pugh/ which discuss

    skip lists.



    Another article worth reading is by Bruce Schneier, "Skip Lists: They're

    easy to implement and they work", Doctor Dobbs Journal, January 1994.



    Tie::Hash::Sorted maintains a hash where keys are sorted. In many cases

    this is faster, uses less memory (because of the way Perl5 manages

    memory), and may be more appropriate for some uses.



    If you need a keyed list that preserves the order of insertion rather

    than sorting keys, see List::Indexed or Tie::IxHash.