title: Example of longest path problem having a NP complexity?
body: <p>I saw on the internet that finding the longest path problem is NP-Complete problem.</p>
  
  <p>For some reason, my teacher tells me that it isn't an NP-complete problem.
  So now I am looking for an example that shows the amount of computation needed for getting the longest path is bigger then polynomial time.</p>
  
  <p>for now, I saw only examples of it having a polynomial complexity time.</p>
  
  <p>anyone can bring me a proof for this problem being NP-complete?</p>