The 28th International Olympiad in Informatics was held in Kazan, Russian Federation in 2016. 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:
      Detecting Molecules
      Roller Coaster Railroad
      Shortcut

Day 2:
      Paint By Numbers
      Unscrambling a Messy Bug
      Aliens

Other materials:
      Test cases
      Solutions to all problems
      Practice problems


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.