Updated to fix a few errors, and replace "push" with "unshift" to cause the next loop iteration to work on the same running node as the previous iteration, until the node is shunted to @final

Woof, what a mess.

The core problem here looks to me as though your algorithm is specifically-designed to reduce the list sub-graphs to a single, contiguous graph. And since it doesn't appear to be designed to expect multiple resultant graphs, it doesn't like them.

There are two things I'm going to ignore for now: the possibility of floating-point-error in the == overload, and the possibility that more than one distinct entry in the initial list shares a starting or ending point. That is, two lists from the set that have the same starting point, or have the same ending point, but are otherwise totally different.

Disclaimer: this is totally pulled out of my ass, and has not been tested. If it doesn't work, fiddle with it a bit and I think you can get it to.

@pointset = (...);
@final = ();

# The basic premise is to pull the first point off of
# the queue and try to attach any of the remaining
# points in the queue to it. If one of them can be
# attached, remove it as well and attach correctly.
# Then, push the now-longer element onto the end of
# the queue.
#
# If you get through the queue without attaching any
# new elements to the top or bottom, then push it
# onto @final, instead. Eventually, @pointset will be
# empty.

while (defined($node = shift(@pointset)))
{
  for $index (0 .. $#pointset)
  {
    if ($node->[0] ==
        $pointset[$index]->[$#{$pointset[$index]}])
    {
      # Add to front of $node
      shift(@$node); # Avoid point at $node->[0] dup'd
      @$node = (@{$pointset[$index]}, @$node);
      # This splice could be used directly above, but I
      # am aiming for clarity in this example.
      splice(@pointset, $index, 1);
      unshift(@pointset, $node);
      next; # Go back to the top of the while-loop
    }
    elsif ($node->[$#$node] == $pointset[$index]->[0])
    {
      # Add to end of $node
      pop(@$node); # Avoid point at $node->[0] dup'd
      @$node = (@$node, @{$pointset[$index]});
      # Again, this splice could be used directly.
      splice(@pointset, $index, 1);
      unshift(@pointset, $node);
      next; # Go back to the top of the while-loop
    }

    # If we reach this point, then none of the other
    # segments could attach to $node, so move it out
    # of the way.
    push(@final, $node);
  }
}

print scalar(@final) . " resulting graphs\n";
print Data::Dumper::Dumper(\@final);
[download]

This isn't as efficient as it could be, since it re-queues the graph and drops out after attaching just one other graph. You could traverse the entire list of sub-graphs, but after enough iterations, you will have the same results (disclaimer about duplicated endpoints notwithstanding).

--rjray

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