You'd pass in your destination node instead of desired length, and your first test would be whether you're starting at your destination. So: 
sub find_path {
  my ($start_at, $end_at, $been_there) = (@_, {});
  if ($start_at == $end_at) {
    return [$start_at];
  }
  else {
    my @try_these = grep { ! $been_there->{$_} } @{$adjacency_list{$st
+art_at}};
    return map {
      my @cdr_list = find_path($_, $end_at, {%$been_there, $start_at =
+> 1});
      map [$start_at, @$_], @cdr_list;
    } @try_these;
  }
}

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In reply to Re^3: find all paths of length n in a graph by Roy Johnson
in thread find all paths of length n in a graph by davidj

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