[comment {-*- tcl -*-}]
[manpage_begin struct::skiplist n 1.3]
[copyright {2000 Keith Vetter}]
[comment {
    This software is licensed under a BSD license as described in tcl/tk
    license.txt file but with the copyright held by Keith Vetter.
}]
[moddesc   {Tcl Data Structures}]
[titledesc {Create and manipulate skiplists}]
[category  {Data structures}]
[require Tcl 8.2]
[require struct::skiplist [opt 1.3]]
[description]
[para]

The [cmd ::struct::skiplist] command creates a new skiplist object
with an associated global Tcl command whose name is
[arg skiplistName]. This command may be used to invoke various
operations on the skiplist. It has the following general form:

[list_begin definitions]
[call [cmd skiplistName] [arg option] [opt [arg "arg arg ..."]]]

[arg Option] and the [arg arg]s determine the exact behavior of the
command.

[list_end]

[para]

Skip lists are an alternative data structure to binary trees. They can
be used to maintain ordered lists over any sequence of insertions and
deletions. Skip lists use randomness to achieve probabilistic
balancing, and as a result the algorithms for insertion and deletion
in skip lists are much simpler and faster than those for binary trees.

[para]

To read more about skip lists see Pugh, William.
[emph {Skip lists: a probabilistic alternative to balanced trees}]
In: Communications of the ACM, June 1990, 33(6) 668-676.

[para]

Currently, the key can be either a number or a string, and comparisons
are performed with the built in greater than operator.

The following commands are possible for skiplist objects:

[list_begin definitions]
[call [arg skiplistName] [method delete] [arg node] [opt [arg node]...]]

Remove the specified nodes from the skiplist.


[call [arg skiplistName] [method destroy]]

Destroy the skiplist, including its storage space and associated command.


[call [arg skiplistName] [method insert] [arg {key value}]]

Insert a node with the given [arg key] and [arg value] into the
skiplist. If a node with that key already exists, then the that node's
value is updated and its node level is returned. Otherwise a new node
is created and 0 is returned.


[call [arg skiplistName] [method search] [arg node] [opt "[const -key] [arg key]"]]

Search for a given key in a skiplist. If not found then 0 is returned.
If found, then a two element list of 1 followed by the node's value is retuned.


[call [arg skiplistName] [method size]]

Return a count of the number of nodes in the skiplist.

[call [arg skiplistName] [method walk] [arg cmd]]

Walk the skiplist from the first node to the last. At each node, the
command [arg cmd] will be evaluated with the key and value of the
current node appended.

[list_end]

[section {BUGS, IDEAS, FEEDBACK}]

This document, and the package it describes, will undoubtedly contain
bugs and other problems.

Please report such in the category [emph {struct :: skiplist}] of the
[uri {http://sourceforge.net/tracker/?group_id=12883} {Tcllib SF Trackers}].

Please also report any ideas for enhancements you may have for either
package and/or documentation.


[keywords skiplist]
[manpage_end]