Dear Limbic,
I tried the following graph and predertimined start and position in code below. But why It gives empty result? Please refer to the visualization of the graph here (http://graph.gafol.net/cESwUMeNd) .

my %graph2 = (
          'read145404_1' => [
                              'read231054_2',
                              'read250449_2'
                            ],
          'read250449_2' => [
                              'read359463_1',
                              'read691358_1',
                              'read937013_1'
                            ],
          'read231054_2' => [
                              'read691358_1',
                              'read359463_1',
                              'read937013_1'
                            ]
        );

my $routes = find_paths('read145404_1', 'read691358_1', \%graph2);

sub find_paths {
    my ($beg, $end, $graph) = @_;

    my $n;
    my %node_to_int = map {$_ => $n++} keys %graph;

    my (@work, @solution);
    for (@{$graph->{$beg}}) {
        if ($_ eq $end) {
            push @solution, "$beg->$end";
            next;
        }
        my $seen = '';
        vec($seen, $node_to_int{$_}, 1) = 1;
        
      
    
        vec($seen, $node_to_int{$beg}, 1) = 1;
    
       
        push @work, ["$beg->$_", $_, $seen];
    }
    while (@work) {
        my $item = pop @work;
        my ($path, $curr, $seen) = @$item;
        for my $node (@{$graph->{$curr}}) {
            my $bit = $node_to_int{$node};
            next if vec($seen, $bit, 1);
            if ($node eq $end) {
                push @solution, "$path $end";
                next;
            }
            my $new_seen = $seen;
            vec($new_seen, $bit, 1) = 1;
            push @work, ["$path->$node", $node, $new_seen];
        }
    }
    

# Return    
print Dumper \@solution;
return \@solution;
}
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