### Graph::Traversal (3)

#### Leading comments

Automatically generated by Pod::Man 2.28 (Pod::Simple 3.28) Standard preamble: ========================================================================

#### 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 chose 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.

#### Backward compatibility

The following parameters are for backward compatibility to Graph 0.2xx:

get_next_root

Like "next_root".

successor

Identical to having "tree_edge" both "non_tree_edge" defined to be the same.

unseen_successor

Like "tree_edge".

seen_successor

Like "seed_edge".

#### 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.