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.\" ========================================================================
.\"
.IX Title "Graph::Traversal 3pm"
.TH Graph::Traversal 3pm "2023-10-31" "perl v5.36.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
Graph::Traversal \- traverse graphs
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
Don't use Graph::Traversal directly, use Graph::Traversal::DFS
or Graph::Traversal::BFS instead.
.PP
.Vb 6
\&    use Graph;
\&    my $g = Graph\->new;
\&    $g\->add_edge(...);
\&    use Graph::Traversal::...;
\&    my $t = Graph::Traversal::...\->new($g, %opt);
\&    $t\->...
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
You can control how the graph is traversed by the various callback
parameters in the \f(CW%opt\fR.  In the parameters descriptions below the
\&\f(CW$u\fR and \f(CW$v\fR are vertices, and the \f(CW$self\fR is the traversal object itself.
.SS "Callback parameters"
.IX Subsection "Callback parameters"
The following callback parameters are available:
.IP "tree_edge" 4
.IX Item "tree_edge"
Called when traversing an edge that belongs to the traversal tree.
Called with arguments ($u, \f(CW$v\fR, \f(CW$self\fR).
.IP "non_tree_edge" 4
.IX Item "non_tree_edge"
Called when an edge is met which either leads back to the traversal tree
(either a \f(CW\*(C`back_edge\*(C'\fR, a \f(CW\*(C`down_edge\*(C'\fR, or a \f(CW\*(C`cross_edge\*(C'\fR).
Called with arguments ($u, \f(CW$v\fR, \f(CW$self\fR).
.IP "pre_edge" 4
.IX Item "pre_edge"
Called for edges in preorder.
Called with arguments ($u, \f(CW$v\fR, \f(CW$self\fR).
.IP "post_edge" 4
.IX Item "post_edge"
Called for edges in postorder.
Called with arguments ($u, \f(CW$v\fR, \f(CW$self\fR).
.IP "back_edge" 4
.IX Item "back_edge"
Called for back edges.
Called with arguments ($u, \f(CW$v\fR, \f(CW$self\fR).
.IP "down_edge" 4
.IX Item "down_edge"
Called for down edges.
Called with arguments ($u, \f(CW$v\fR, \f(CW$self\fR).
.IP "cross_edge" 4
.IX Item "cross_edge"
Called for cross edges.
Called with arguments ($u, \f(CW$v\fR, \f(CW$self\fR).
.IP "pre" 4
.IX Item "pre"
.PD 0
.IP "pre_vertex" 4
.IX Item "pre_vertex"
.PD
Called for vertices in preorder.
Called with arguments ($v, \f(CW$self\fR).
.IP "post" 4
.IX Item "post"
.PD 0
.IP "post_vertex" 4
.IX Item "post_vertex"
.PD
Called for vertices in postorder.
Called with arguments ($v, \f(CW$self\fR).
.IP "first_root" 4
.IX Item "first_root"
Called when choosing the first root (start) vertex for traversal.
Called with arguments ($self, \f(CW$unseen\fR) where \f(CW$unseen\fR is a hash
reference with the unseen vertices as keys.
.IP "next_root" 4
.IX Item "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 ($self, \f(CW$unseen\fR) where \f(CW$unseen\fR is a hash reference with
the unseen vertices as keys.  If you want only the first reachable
subgraph to be processed, set the next_root to \f(CW\*(C`undef\*(C'\fR.
.IP "start" 4
.IX Item "start"
Identical to defining \f(CW\*(C`first_root\*(C'\fR and undefining \f(CW\*(C`next_root\*(C'\fR.
.IP "next_alphabetic" 4
.IX Item "next_alphabetic"
Set this to true if you want the vertices to be processed in
alphabetic order (and leave first_root/next_root undefined).
.IP "next_numeric" 4
.IX Item "next_numeric"
Set this to true if you want the vertices to be processed in
numeric order (and leave first_root/next_root undefined).
.IP "next_successor" 4
.IX Item "next_successor"
Called when choosing the next vertex to visit.  Called with arguments
($self, \f(CW$next\fR) where \f(CW$next\fR is a hash reference with the possible
next vertices as keys.  Use this to provide a custom ordering for
choosing vertices, as opposed to \f(CW\*(C`next_numeric\*(C'\fR or \f(CW\*(C`next_alphabetic\*(C'\fR.
.PP
The parameters \f(CW\*(C`first_root\*(C'\fR and \f(CW\*(C`next_successor\*(C'\fR have a 'hierarchy'
of how they are determined: if they have been explicitly defined, use
that value.  If not, use the value of \f(CW\*(C`next_alphabetic\*(C'\fR, if that has
been defined.  If not, use the value of \f(CW\*(C`next_numeric\*(C'\fR, if that has
been defined.  If not, the next vertex to be visited is chosen randomly.
.SS "Methods"
.IX Subsection "Methods"
The following methods are available:
.IP "unseen" 4
.IX Item "unseen"
Return the unseen vertices in random order.
.IP "seen" 4
.IX Item "seen"
Return the seen vertices in random order.
.IP "seeing" 4
.IX Item "seeing"
Return the active fringe vertices in random order.
.IP "preorder" 4
.IX Item "preorder"
Return the vertices in preorder traversal order.
.IP "postorder" 4
.IX Item "postorder"
Return the vertices in postorder traversal order.
.IP "vertex_by_preorder" 4
.IX Item "vertex_by_preorder"
.Vb 1
\&    $v = $t\->vertex_by_preorder($i)
.Ve
.Sp
Return the ith (0..$V\-1) vertex by preorder.
.IP "preorder_by_vertex" 4
.IX Item "preorder_by_vertex"
.Vb 1
\&    $i = $t\->preorder_by_vertex($v)
.Ve
.Sp
Return the preorder index (0..$V\-1) by vertex.
.IP "vertex_by_postorder" 4
.IX Item "vertex_by_postorder"
.Vb 1
\&    $v = $t\->vertex_by_postorder($i)
.Ve
.Sp
Return the ith (0..$V\-1) vertex by postorder.
.IP "postorder_by_vertex" 4
.IX Item "postorder_by_vertex"
.Vb 1
\&    $i = $t\->postorder_by_vertex($v)
.Ve
.Sp
Return the postorder index (0..$V\-1) by vertex.
.IP "preorder_vertices" 4
.IX Item "preorder_vertices"
Return a hash with the vertices as the keys and their preorder indices
as the values.
.IP "postorder_vertices" 4
.IX Item "postorder_vertices"
Return a hash with the vertices as the keys and their postorder
indices as the values.
.IP "tree" 4
.IX Item "tree"
Return the traversal tree as a graph.
.IP "has_state" 4
.IX Item "has_state"
.Vb 1
\&    $t\->has_state(\*(Aqs\*(Aq)
.Ve
.Sp
Test whether the traversal has state 's' attached to it.
.IP "get_state" 4
.IX Item "get_state"
.Vb 1
\&    $t\->get_state(\*(Aqs\*(Aq)
.Ve
.Sp
Get the state 's' attached to the traversal (\f(CW\*(C`undef\*(C'\fR if none).
.IP "set_state" 4
.IX Item "set_state"
.Vb 1
\&    $t\->set_state(\*(Aqs\*(Aq, $s)
.Ve
.Sp
Set the state 's' attached to the traversal.
.IP "delete_state" 4
.IX Item "delete_state"
.Vb 1
\&    $t\->delete_state(\*(Aqs\*(Aq)
.Ve
.Sp
Delete the state 's' from the traversal.
.SS "Special callbacks"
.IX Subsection "Special callbacks"
If in a callback you call the special \f(CW\*(C`terminate\*(C'\fR method,
the traversal is terminated, no more vertices are traversed.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Graph::Traversal::DFS, Graph::Traversal::BFS
.SH "AUTHOR AND COPYRIGHT"
.IX Header "AUTHOR AND COPYRIGHT"
Jarkko Hietaniemi \fIjhi@iki.fi\fR
.SH "LICENSE"
.IX Header "LICENSE"
This module is licensed under the same terms as Perl itself.