JOI Open Contest 2021

This is an IOI-like open competition for students at schools for secondary education. The main purpose of this contest is to give an opportunity to Japanese delegations and candidates of delegations for training and practice. But the contest itself is open to everybody. Everybody is welcome to attend JOI Open Contest 2021!

The duration of the contest is 5 hours. You can choose start time from specified range freely. After the duration finishes, we will open the judging server for one week. Interested contestants can improve and resubmit their solutions by themselves.

Registration will be open before the contest. A link to the registration page will appear on this page before the beginning of the contest. Contestants can register on the contest site by themselves from the right before the beginning of the contest until the end of it.

No prizes will be given to the contestants.

The ranking will be public during and after the contest. It includes your username provided via the registration form.

Contest Information

JOI Open Contest 2021
Contest System
Contest duration
5 hours
The number of tasks
3 tasks
English, Japanese
Date and Time
Sunday, June 6, 2021 13:00 - Monday, June 7, 2021 13:00 +0900 (JST)
Sunday, June 6, 2021 04:00 - Monday, June 7, 2021 04:00 (UTC/GMT)
You can choose start time from above freely and the duration is 5 hours.
However, if you start competing after 08:00 (JST), competition ends at 13:00 (JST) and the duration is less than 5 hours.


Rules that are same as IOI 2017 Rule:

Rules that are not same as IOI 2017 Rule:

Contest Site


We appreciate your feedback on our contest! Please answer the questionnaire after the contest.




Sample Sources

Test Data


joiopen at


Creative Commons License
The tasks for JOI Open Contest 2021 by JCIOI (the Japanese Committee for the IOI) is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. If you need a license other than a Creative Commons Attribution-ShareAlike 4.0 International License (CC BY-SA 4.0), please ask JCIOI.