I still like my idea of the "cracked screen", where you can define some of the nodes as not working, or proviging an info about "cracks" in the input, for example ["FJ"] cracks would mean that you cannot draw a segment from F to J.

I don't think that a tolerance check will help much, because numbers can go very high in magnitude, and it is difficult to find an absolute tolerance for such large numbers. If floats would to be kept, I think that relative tolerance would work better. But in general, I think that doubles are not necessary for this problem at all, and I would redo it with integers like long, bigint, or carefully capped int.

How about now?