23 lines
316 B
Perl
23 lines
316 B
Perl
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use 5.20.0;
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use warnings;
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use experimental qw/
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signatures
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postderef
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/;
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use Graph::Directed;
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my $g = Graph::Directed->new;
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while(<>) {
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/Step (.).*before step (.)/;
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$g->add_edge( $1 => $2 );
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}
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while( my @x = sort $g->predecessorless_vertices ) {
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print $x[0];
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$g->delete_vertex($x[0]);
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}
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