I have done this kind of triangle mesh "fixing" myself (in my triangle
mesh smoother program).
  The idea is quite simple:

  1. Take the first triangle and mark it as 'handled'.

  2. Search all the triangles which are adjacent to this one and are
     not marked as 'handled'. An adjacent triangle is one that shares two
     vertices with this one.

  3. Check if the adjacent triangle is ordered correctly. That is, if the
     shared vertices are listed in inverse order in the adjacent triangle than
     in the current triangle, then it's ok. If they are listed in the same
     order, then you have to swap the other triangle.

  4. Now mark these adjacent triangles as 'handled' and for each one of them
     make recursively steps 2, 3 and 4 until no more triangles are found.

  5. After that, search for some unhandled triangle. If the mesh consisted of
     one contiguous surface, you'll not find any, but you have to do this
     because the mesh may consist of several separate parts. If you find
     an unhandled triangle, make all steps 1, 2, 3, 4 and 5 for it.


  This works pretty well, but it's very slow, specially with big meshes.
The slowest step is the second one (ie. the searching). There's probably some
way of speeding it up using some tree structure or hash table.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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