Due to the COVID-19 pandemic, IOI 2020 has been postponed. More info is available on the official website.
Update IOI 2020 is postponed
The 21st International Olympiad in Informatics was held in Plovdiv, Bulgaria in 2009. There were two competition days, with 4 tasks given to the competitors on each day. You can see the tasks, test cases and solutions below.
Solutions and booklet
Solutions (source codes)
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.