The International Olympiad in Informatics (IOI) is an annual competitive programming competition and one of the International Science Olympiads for secondary school students. The first IOI was held in 1989 in Pravetz, Bulgaria. Each country sends a team of up to four students, plus one team leader, one deputy leader, and guests. Students in each country are selected for their country's team through national computing contests. Students at the IOI compete on an individual basis. There is no official team ranking. The contest consists of two days of solving six complicated algorithmic tasks by writing computer programs in C++. All task materials are published on each year's contest website soon after the competition ends.
Competition structure and participation
On each of the two competition days, the competitors are typically given three problems which they have to solve in five hours. Each student works on their own to solve the problems with no outside help, specifically no communication with other contestants, books, web access, etc. Contestants are typically allowed to bring non-programmable wired keyboards and mice. Usually to solve a task the contestant has to write a computer program (in C++) and submit it before the five-hour competition time ends. The program is graded based on secret test data. Since IOI 2010, tasks are divided into subtasks with graduated difficulty, and points are awarded only when all tests for a particular subtask yield correct results, within specific time and memory limits. In some cases, the contestant's program has to interact with a secret computer library, which allows problems where the input is not fixed, but depends on the program's actions – for example in game problems (a.k.a. interactive problems). Another type of problem has the inputs publicly available, for these, the contestants have to submit an output file instead of a program, and it is up to them whether they obtain the output files by writing a program (possibly exploiting special characteristics of the input), or by hand, or by a combination of these means. Pascal has been removed as an available programming language as of 2019.:11 IOI 2010 for the first time had a live web scoreboard with real-time provisional results. Submissions will be scored as soon as possible during the contest, and the results posted. Contestants will be aware of their scores, but not others', and may resubmit to improve their scores. Starting from 2012, IOI has been using the Contest Management System (CMS) for developing and monitoring the contest. The scores from the two competition days and all problems are summed up separately for each contestant. Medals are awarded depending on their relative total score. The top 50% of the contestants are awarded medals, such that the relative number of gold : silver : bronze : no medal is approximately 1:2:3:6 (thus 1/12 of the contestants get a gold medal). Prior to IOI 2010, students who did not receive medals did not have their scores published, although the scores of students who did not receive medals are still not available in the official results, they are known from the live web scoreboard. In IOI 2012 the top 3 nations ranked by aggregate score (Russia, China and USA) were subsequently awarded during the closing ceremony. Analysis of female performance shows 77.9% of women obtain no medal, while 49.2% of men obtain no medal. "The average female participation was 4.4% in 1989–1994 and 2.2% in 1996–2014." It also suggests much higher participation of women on the national level, claiming sometimes double-digit percentages in total participation on the first stage. President of the IOI (2011-2014), Richard Forster, says the competition has difficulty attracting women and that in spite of trying to solve it, "none of us have hit on quite what the problem is, let alone the solution." The European Girls’ Olympiad in Informatics (EGOI), which was first held in 2021, was started with the goal of increasing female participation at IOI and other Informatics Olympiads. At the 2017 competition held in Iran, the Israeli team was initially not allowed to compete. After Israel appealed, Innopolis University (Russian Federation) offered to host the Israeli team offsite.:11 Due to visa issues, the full USA team was unable to attend, although one contestant Zhezheng Luo was able to attend by traveling with the Chinese team and winning gold medal and 3rd place in standings. In IOI 2019 held in Azerbaijan, the Armenia team did not participate due to the dispute between the two countries, despite the guarantees provided and official invitation letter sent by the host Azerbaijan. Due to the COVID-19 pandemic, both the IOI 2020 and IOI 2021, originally scheduled to be hosted by Singapore, were held as online contests. The IOI 2022, hosted by Indonesia, was held as a hybrid event, with around 25% of the contestants participating online. In response to the invasion of Ukraine, students from Russia and Belarus can only participate as individuals under the IOI flag but not as national delegations starting from IOI 2022, and they would only participate online for IOI 2022. From 2023 onwards they would participate in person, but under the IOI flag. In response to the conflict and humanitarian crisis in Gaza, over two thirds of the delegations voted to sanction Israel so that starting with IOI 2025, Israeli students can only participate as individuals under the IOI flag rather as a national delegation. At the 2026 IOI in Tashkent, Yotam Budnik, a student from Israel, won a gold medal but was disqualified after displaying an Israeli flag during the awards ceremony, which violated the sanctions introduced in 2024. His result was removed from the official rankings and his certificate was revoked. Budnik said that he wanted to protest the restrictions imposed on Israeli contestants, which he considered unfair, and that he believed politics should not be involved in a computer science competition.
Members
Former members
Summary
All-time medal table
Top
All https://stats.ioinformatics.org/countries/ Since 1989 to 2025: In almost every edition, the top 10% of participants receive gold, the next 20% receive silver, and the next 30% receive bronze.
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