The 17th International Olympiad in Informatics was held in Nowy Sacz, Poland in 2005. 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:
      Garden
      Mean Sequence
      Mountain

Day 2:
      Birthday
      Rectangle Game
      Rivers

Other materials:
      Test cases
      Solutions and booklet


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.