Graph::Traversal(3p)

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. If not supplied, defaults to the same as "next_root".

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.

SEE ALSO
Graph::Traversal::DFS, Graph::Traversal::BFS

AUTHOR AND COPYRIGHT
Jarkko Hietaniemi jhi@iki.fi

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