Please visit the following links for useful materials regarding the Olympiad:

  1. http://plo-in.org/resources
  2. http://www.ioling.org/problems/
  3. http://www.uklo.org/example-questions
  4. http://www.nacloweb.org/
  5. 2017 HLON solutions: http://2017.hlon.org/solutions,
  6. 2018 HLON solutions: https://hlon.org/solutions/