Jarkko Hietaniemi > Graph-0.96 > Graph::UnionFind

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NAME ^

Graph::UnionFind - union-find data structures

SYNOPSIS ^

    use Graph::UnionFind;
    my $uf = Graph::UnionFind->new;

    # Add the vertices to the data structure.
    $uf->add($u);
    $uf->add($v);

    # Join the partitions of the vertices.
    $uf->union( $u, $v );

    # Find the partitions the vertices belong to
    # in the union-find data structure.  If they
    # are equal, they are in the same partition.
    # If the vertex has not been seen,
    # undef is returned.
    my $pu = $uf->find( $u );
    my $pv = $uf->find( $v );
    $uf->same($u, $v) # Equal to $pu eq $pv. 

    # Has the union-find seen this vertex?
    $uf->has( $v )

DESCRIPTION ^

Union-find is a special data structure that can be used to track the partitioning of a set into subsets (a problem known also as disjoint sets).

Graph::UnionFind() is used for Graph::connected_components(), Graph::connected_component(), and Graph::same_connected_components() if you specify a true union_find parameter when you create an undirected graph.

Note that union-find is one way: you cannot (easily) 'ununion' vertices once you have 'unioned' them. This means that if you delete edges from a union_find graph, you will get wrong results from the Graph::connected_components(), Graph::connected_component(), and Graph::same_connected_components().

API

add
    $uf->add($v)

Add the vertex v to the union-find.

union
    $uf->union($u, $v)

Add the edge u-v to the union-find. Also implicitly adds the vertices.

has
    $uf->has($v)

Return true if the vertex v has been added to the union-find, false otherwise.

find
    $uf->find($v)

Return the union-find partition the vertex v belongs to, or undef if it has not been added.

new
    $uf = Graph::UnionFind->new()

The constructor.

same
    $uf->same($u, $v)

Return true of the vertices belong to the same union-find partition the vertex v belongs to, false otherwise.

AUTHOR AND COPYRIGHT ^

Jarkko Hietaniemi jhi@iki.fi

LICENSE ^

This module is licensed under the same terms as Perl itself.

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