Are there any problems which are known to be both NP-complete and EXPTIME-compelte? My guess is no, because we know that $P$ is not equal to $EXPTIME$ and EXPTIME-complete problems are not in $P$, and hence a problem that was both NP-complete and EXPTIME-complete would imply $P \not= NP$. Is my thinking correct?

Note that in a difference in notation, here $EXPTIME=EXP$.


1 Answer 1


No, that is not currently known. If such a problem were known, it would prove that:


Incidentally, it would also prove that $NP=PSPACE$, because it is known that:

$$P \subseteq NP \subseteq PSPACE \subseteq EXPTIME$$

We don't know which of these subset relations are strict subset relations, but at least one of them must be, because by the time hierarchy theorem:

$$P \subset EXPTIME$$

  • 1
    $\begingroup$ So just to verify, from what you stated this would imply $P \not= NP$ since we need a strict subset, and since NP and PSPACE and EXPTIME would all be equal, this would mean that the only possible strict subset is P is a strict subset of NP? Thanks for the answer! $\endgroup$
    – user918212
    Aug 9, 2022 at 1:26
  • $\begingroup$ I suppose that's true, yes. $\endgroup$
    – Pseudonym
    Aug 9, 2022 at 4:04

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