# International Olympiad in Informatics

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 no programable 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 to increscent female participants at IOI and other Informatics Olympiads.
In IOI 2017 held in Iran, due to not being able to participate in Iran, the Israeli students participated in an offsite competition organized by IOI in Russia.$^{:11}$ 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, but they may return on-site from IOI 2023 onwards.
In response to the conflict and humanitarian crisis in Gaza, students from Israel can only participate as individuals under the IOI flag but not as a national delegation from IOI 2025 onwards. Over two thirds of the delegations voted in favour of the sanction in the IOI General Assembly.

## Members

* Albania
* Algeria
* Argentina
* Armenia
* Australia
* Austria
* Azerbaijan
* Bangladesh
* Belarus
* Belgium
* Bolivia
* Bosnia and Herzegovina
* Brazil
* Bulgaria
* Canada
* Chile
* China
* Colombia
* Croatia
* Cuba
* Cyprus
* Czech Republic
* Denmark
* Dominican Republic
* Ecuador
* Egypt
* El Salvador
* Estonia
* Finland
* France
* Georgia
* Germany
* Greece
* Hong Kong
* Hungary
* Iceland
* India
* Indonesia
* Iran
* Ireland
* Israel
* Italy
* Japan
* Jordan
* Kazakhstan
* Kyrgyzstan
* Latvia
* Libya
* Lithuania
* Luxembourg
* Macau
* Malaysia
* Mexico
* Moldova
* Mongolia
* Montenegro
* Morocco
* Netherlands
* New Zealand
* Nigeria
* North Macedonia
* Norway
* Pakistan
* Palestine
* Peru
* Philippines
* Poland
* Portugal
* Romania
* Russia
* Rwanda
* Saudi Arabia
* Serbia
* Singapore
* Slovakia
* Slovenia
* South Africa
* South Korea
* Spain
* Sri Lanka
* Sweden
* Switzerland
* Syria
* Taiwan
* Tajikistan
* Thailand
* Tunisia
* Turkey
* Turkmenistan
* Ukraine
* United Kingdom
* United States
* Uzbekistan
* Venezuela
* Vietnam

### Former members

* Gabon
* Ghana
* Kuwait
* Madagascar
* Malta
* Mauritius
* Mozambique
* Sudan
* Trinidad and Tobago
* United Arab Emirates
* Zimbabwe

## Summary

| Number | Year | Dates | Host country | Host city |
| 1 | 1989 | May 16–19 | Bulgaria | Pravetz |
| 2 | 1990 | July 15–21 | Belarus, Soviet Union | Minsk |
| 3 | 1991 | May 19–25 | Greece | Athens |
| 4 | 1992 | July 11–21 | Germany | Bonn |
| 5 | 1993 | October 16–25 | Argentina | Mendoza |
| 6 | 1994 | July 3–10 | Sweden | Haninge |
| 7 | 1995 | June 26 – July 3 | Netherlands | Eindhoven |
| 8 | 1996 | July 25 – August 2 | Hungary | Veszprém |
| 9 | 1997 | November 30 – December 7 | South Africa | Cape Town |
| 10 | 1998 | September 5–12 | Portugal | Setúbal |
| 11 | 1999 | October 9–16 | Turkey | Antalya-Belek |
| 12 | 2000 | September 23–30 | China | Beijing |
| 13 | 2001 | July 14–21 | Finland | Tampere |
| 14 | 2002 | August 18–25 | Korea Rep. | Yong-In |
| 15 | 2003 | August 16–23 | United States | Kenosha, Wisconsin |
| 16 | 2004 | September 11–18 | Greece | Athens |
| 17 | 2005 | August 18–25 | Poland | Nowy Sącz |
| 18 | 2006 | August 13–20 | Mexico | Mérida, Yucatán |
| 19 | 2007 | August 15–22 | Croatia | Zagreb |
| 20 | 2008 | August 16–23 | Egypt | Cairo |
| 21 | 2009 | August 8–15 | Bulgaria | Plovdiv |
| 22 | 2010 | August 14–21 | Canada | Waterloo, Ontario |
| 23 | 2011 | July 22–29 | Thailand | Pattaya |
| 24 | 2012 | September 23–30 | Italy | Sirmione and Montichiari |
| 25 | 2013 | July 6–13 | Australia | Brisbane |
| 26 | 2014 | July 13–20 | Taiwan | Taipei |
| 27 | 2015 | July 26 – August 2 | Kazakhstan | Almaty |
| 28 | 2016 | August 12–19 | Russia | Kazan |
| 29 | 2017 | July 28 – August 4 | Iran | Tehran |
| 30 | 2018 | September 1–8 | Japan | Tsukuba |
| 31 | 2019 | August 4–11 | Azerbaijan | Baku |
| 32 | 2020 | September 13–19 | Singapore | online |
| 33 | 2021 | June 19–25 | Singapore | online |
| 34 | 2022 | August 7–15 | Indonesia | Yogyakarta |
| 35 | 2023 | August 28 – September 4 | Hungary | Szeged |
| 36 | 2024 | September 1–8 | Egypt | Alexandria |
| 37 | 2025 | July 27 – August 3 | Bolivia | Sucre |
| 38 | 2026 | | Uzbekistan | |
| 39 | 2027 | | Germany | Potsdam |

## All-time medal table

As of 2024 :
| Rank | Nation | Gold | Silver | Bronze | Total |
| 1 | China (CHN) | 102 | 28 | 12 | 142 |
| 2 | Russia (RUS) | 68 | 40 | 12 | 120 |
| 3 | United States (USA) | 68 | 39 | 16 | 123 |
| 4 | South Korea (KOR) | 49 | 50 | 28 | 127 |
| 5 | Poland (POL) | 44 | 52 | 35 | 131 |
| 6 | Japan (JPN) | 37 | 30 | 10 | 77 |
| 7 | Romania (ROU) | 34 | 60 | 37 | 131 |
| 8 | Iran (IRN) | 32 | 67 | 24 | 123 |
| 9 | Bulgaria (BGR) | 27 | 55 | 45 | 127 |
| 10 | Slovakia (SVK) | 26 | 45 | 36 | 107 |
| Totals (10 entries) | Totals (10 entries) | 487 | 466 | 255 | 1,208 |

## Multiple IOI winners

The following is a list of the top performers in the history of the IOI. The $^P$ sign indicates a perfect score, a rare achievement in IOI history. The $^U$ sign indicates an unofficial participation, where a contestant participated in a host's second team. Also, first (I), second (II) and third (III) places among gold medalists are indicated where appropriate.
| Name | Team | Years | Years | Years | Years | Years | Years | Years |
| Gennady Korotkevich | Belarus | G(II) 2012 | G$^P$(I) 2011 | G(I) 2010 | G(I) 2009 | G 2008 | G 2007 | S 2006 |
| Bruce Merry | South Africa | G 2001 | G 2000 | S 1999 | B 1998 | B 1997 | B 1996 | |
| Rumen Hristov | Bulgaria | G 2012 | G 2011 | G(II) 2010 | S 2009 | S 2008 | | |
| Hristo Venev | Bulgaria | G 2016 | G 2015 | G 2014 | G 2013 | S 2012 | | |
| Encho Mishinev | Bulgaria | G 2017 | G 2014 | S 2016 | S 2015 | S 2013 | | |
| Egor Lifar | Russia | G 2021 | G 2019 | S 2020 | S 2018 | S 2017 | | |
| Harris Leung | Hong Kong | G 2021 | G(III) 2020 | S 2019 | B 2018 | B 2017 | | |
| Zixiang Zhou | Canada | G 2022 | G 2021 | G 2020 | G(III) 2019 | S 2018 | | |
| Wolfgang Thaller | Austria | G 1997 | G 1996 | S 1999 | S 1998 | | | |
| Andrzej Gąsienica-Samek | Poland | G 1999 | G 1998 | G 1997 | S 1996 | | | |
| Martin Pettai | Estonia | G 2002 | G 2001 | G 2000 | S 1999 | | | |
| Alex Schwendner | United States | G 2005 | G 2003 | S 2004 | S 2002 | | | |
| Filip Wolski | Poland | G(I) 2006 | G 2005 | G 2004 | G 2003 | | | |
| Goran Žužić | Croatia | G 2008 | G 2007 | S 2009 | B 2006 | | | |
| Vlad Alexandru Gavrilă | Romania | G 2013 | G 2012 | S 2011 | B 2010 | | | |
| Eduard Batmendijn | Slovakia | G 2015 | G 2013 | G 2012 | S 2014 | | | |
| Rareș Darius Buhai | Romania | G 2015 | G 2014 | G 2013 | G 2012 | | | |
| Yuta Takaya | Japan | G(I) 2017 | G 2016 | G 2015 | G 2014 | | | |
| Nikoloz Birkadze | Georgia | G 2020 | G 2019 | G 2018 | S 2017 | | | |
| Dorijan Lendvaj | Croatia | G 2022 | G 2021 | S 2020 | B 2019 | | | |
| Patrick Pavić | Croatia | G 2022 | G 2021 | G 2020 | S 2019 | | | |
| Fredrik Huss | Sweden | G$^P$(I) 1993 | G$^P$(I) 1992 | S 1991 | | | | |
| Martin Mareš | Czech Republic | G 1995 | G 1994 | G$^P$(I) 1993 | | | | |
| Vladimir Martianov | Russia | G 1999 | G$^P$(I) 1998 | G(I) 1997 | | | | |
| John Pardon | United States | G 2007 | G 2006 | G 2005 | | | | |
| Marcin Andrychowicz | Poland | G 2008 | G 2007 | G 2006 | | | | |
| Neal Wu | United States | G 2010 | G 2009 | G 2008 | | | | |
| Shogo Murai | Japan | G 2012 | G 2011 | G 2010 | | | | |
| Scott Wu | United States | G$^P$(I) 2014 | G 2013 | G 2012 | | | | |
| Jarosław Kwiecień | Poland | G 2016 | G 2015 | G 2014 | | | | |
| Vladimir Romanov | Russia | G 2019 | G 2018 | G 2017 | | | | |
| Masataka Yoneda | Japan | G 2020 | G 2019 | G$^U$ 2018 | | | | |
| Daiki Kodama | Japan | G 2023 | G 2022 | G 2021 | | | | |

## Feeder competitions

Most participating countries use feeder competitions to select their team. A number of these are listed below:
* Australian Informatics Olympiad
* British Informatics Olympiad
* Canadian Computing Olympiad
   * The participants of which are chosen from the Canadian Computing Competition
* Central European Olympiad in Informatics
* Indian Computing Olympiad
* National Olympiad in Informatics
* National Olympiad in Informatics, China
* Olimpiada Națională de Informatică [ro]
* Nederlandse Informatica Olympiade [nl]
* Olimpiada Mexicana de Informática [es]
* South African Computer Olympiad
* Syrian Olympiad in Informatics
* United States of America Computing Olympiad
* Moroccan Olympiad in Informatics
* All Ireland Programming Olympiad
* Indonesian Olympiad in Informatics
* Egyptian Olympiad in Informatics
* National Olympiad in Informatics - Philippines
* Bundeswettbewerb Informatik - Germany
* Vietnamese Olympiad in Informatics