I want to prove that this problem to find whether the crossing number of any given graph is K or not, is NP-Hard. I don't know how to do this. Can someone help me with this ?

  • $\begingroup$ Are you familiar with reductions? Yes: please specify where exactly you are stuck or state your doubt. No: please go through a standard textbook/material on proving NP-completeness first. $\endgroup$
    – codeR
    Commented Apr 24 at 8:19
  • $\begingroup$ The crossing number problem is well studied; a simple web search would have revealed that. Here's one (probably original) proof: doi.org/10.1137/0604033 $\endgroup$
    – codeR
    Commented Apr 24 at 8:22

1 Answer 1


The crossing number problem has been well studied. From wiki:

In general, determining the crossing number of a graph is hard; Garey and Johnson showed in 1983 that it is an NP-hard problem [ref].

In fact the problem remains NP-hard even when restricted to cubic graphs [ref2] and to near-planar graphs (graphs that become planar after removal of a single edge) [ref3].

Also see this stackexchange discussion.


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