NAME

Graph::Traversal - traverse graphs

SYNOPSIS

Don't use Graph::Traversal directly, use Graph::Traversal::DFS or Graph::Traversal::BFS instead.

    use Graph;
    my $g = Graph->new;
    $g->add_edge(...);
    use Graph::Traversal::...;
    my $t = Graph::Traversal::...->new($g, %opt);
    $t->...

DESCRIPTION

You can control how the graph is traversed by the various callback parameters in the %opt. In the parameters descriptions below the $u and $v are vertices, and the $self is the traversal object itself.

Callback parameters

The following callback parameters are available:

tree_edge: Called when traversing an edge that belongs to the traversal tree. Called with arguments ($u, $v, $self).
non_tree_edge: Called when an edge is met which either leads back to the traversal tree (either a "back_edge", a "down_edge", or a "cross_edge"). Called with arguments ($u, $v, $self).
pre_edge: Called for edges in preorder. Called with arguments ($u, $v, $self).
post_edge: Called for edges in postorder. Called with arguments ($u, $v, $self).
back_edge: Called for back edges. Called with arguments ($u, $v, $self).
down_edge: Called for down edges. Called with arguments ($u, $v, $self).
cross_edge: Called for cross edges. Called with arguments ($u, $v, $self).
pre
pre_vertex: Called for vertices in preorder. Called with arguments ($v, $self).
post
post_vertex: Called for vertices in postorder. Called with arguments ($v, $self).
first_root: Called when choosing the first root (start) vertex for traversal. Called with arguments ($self, $unseen) where $unseen is a hash reference with the unseen vertices as keys.
next_root: Called when choosing the next root (after the first one) vertex for traversal (useful when the graph is not connected). Called with arguments ($self, $unseen) where $unseen is a hash reference with the unseen vertices as keys. If you want only the first reachable subgraph to be processed, set the next_root to "undef".
start: Identical to defining "first_root" and undefining "next_root".
next_alphabetic: Set this to true if you want the vertices to be processed in alphabetic order (and leave first_root/next_root undefined).
next_numeric: Set this to true if you want the vertices to be processed in numeric order (and leave first_root/next_root undefined).
next_successor: Called when choosing the next vertex to visit. Called with arguments ($self, $next) where $next is a hash reference with the possible next vertices as keys. Use this to provide a custom ordering for choosing vertices, as opposed to "next_numeric" or "next_alphabetic".

The parameters "first_root" and "next_successor" have a 'hierarchy' of how they are determined: if they have been explicitly defined, use that value. If not, use the value of "next_alphabetic", if that has been defined. If not, use the value of "next_numeric", if that has been defined. If not, the next vertex to be visited is chosen randomly.

Methods

The following methods are available:

unseen

Return the unseen vertices in random order.

seen

Return the seen vertices in random order.

seeing

Return the active fringe vertices in random order.

preorder

Return the vertices in preorder traversal order.

postorder

Return the vertices in postorder traversal order.

vertex_by_preorder

    $v = $t->vertex_by_preorder($i)

Return the ith (0..$V-1) vertex by preorder.

preorder_by_vertex

    $i = $t->preorder_by_vertex($v)

Return the preorder index (0..$V-1) by vertex.

vertex_by_postorder

    $v = $t->vertex_by_postorder($i)

Return the ith (0..$V-1) vertex by postorder.

postorder_by_vertex

    $i = $t->postorder_by_vertex($v)

Return the postorder index (0..$V-1) by vertex.

preorder_vertices

Return a hash with the vertices as the keys and their preorder indices as the values.

postorder_vertices

Return a hash with the vertices as the keys and their postorder indices as the values.

tree

Return the traversal tree as a graph.

has_state

    $t->has_state('s')

Test whether the traversal has state 's' attached to it.

get_state

    $t->get_state('s')

Get the state 's' attached to the traversal ("undef" if none).

set_state

    $t->set_state('s', $s)

Set the state 's' attached to the traversal.

delete_state

    $t->delete_state('s')

Delete the state 's' from the traversal.

Special callbacks

If in a callback you call the special "terminate" method, the traversal is terminated, no more vertices are traversed.

AUTHOR AND COPYRIGHT

Jarkko Hietaniemi jhi@iki.fi

LICENSE

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