The 18th International Olympiad in Informatics was held in Mérida, Yucatán, Mexico in 2006. There were two competition days, with 3 tasks given to the competitors on each day. You can see the tasks, test cases and solutions below.

Day 1:
      Forbidden Subgraph
      Pyramid
      Deciphering the Mayan Writing

Day 2:
      A Black Box Game
      The Valley of Mexico
      Joining Points

Other materials:
      Test cases
      Solutions to all problems
      Practice tasks


Note that the grading model changed at IOI'94 and beyond.
Before IOI 1994, a human evaluator would sit behind the competitor's computer and do the testing manually (enter test data through the keyboard, check the output on the screen). Starting from IOI 1994, an automatic grading process is used, with test input defined in files.