dsu

Post-BOJ plans on linking other OJs to solved.ac

Draft Apr 30, 2026

TLDR

• We will support other OJs.
• Current top priority is to link other OJs to find same problems in BOJ, and make the problems solvable if you know the BOJ problem ID.
  • This is an effort to recover 'broken links' of the BOJ -- many online resources (especially in Korean) rely on the BOJ problem IDs.
• In the long term, we plan to link as many OJs as possible and provide the library and features just like we did with the BOJ.

Plans on Linking

We will have our own...

• ID/password account system. Basic things are already done by Apr 26th.
  • We plan to allow logging in by other OJs' accounts in the future.
• Problem numbering system.
  • We will basically use the same number scheme as the BOJ, which starts from #1000.
  • For problems #1000..#35515, most of the problem numbers will match the BOJ's numbers, excluding problems such as duplicate problems, and the problems with subtasks will get a numbering for each task - it is a N:M mapping.
  • For other OJs, if the problem is identical of that in the BOJ, we 'link' the existing ID to the foreign OJ's ID. Otherwise we assign them starting from #35516.
  • For instance, the problem Scenery will be solved.ac #14640 = BOJ #14640 = Kattis scenery = QOJ #2774 = ...

Step I: Syncing the Problems

First, we would like to sync the problems fron other OJs. To do this we will contact and/or accept contacts from other OJs' administrators.

• Foreign OJs do not have to do anything in this step. If they have an API, we will use them, and if they have not, we will write a crawler to run a recurring job.
• The contributors from the BOJ will assign solved.ac problem IDs.
  • This means that the problems in the foreign OJs will get the difficulty levels assigned to their problems (which had an identical version in the BOJ, for now)
  • The users of the foreign OJs can get used to the level scheme, and many of the lost problems of the BOJ will be recovered in this step.
  • solved.ac would help accelerating this process by matching the source of the problems, or mass-comparing descriptions with LLM, etc.

Step II: Syncing the Users

Then we sync the users. A solved.ac user can link multiple foreign OJs' accounts. You can think of the way that CLIST does, but with more trust.

• Foreign OJs should allow us to verify whether the user owns her account or not, by but not limited to the following means:
  • Allowing us as a 3rd party to use the judge's OAuth authentication flow (recommended)
  • Allowing us to read an arbitrary user's submission history. We will prompt the user to make a submission to some random problem. An example way of doing this
  • Allowing us to read a user's profile, and allowing the user to write an arbitrary string to their profile, etc.

This enables the users from the other OJs to be able to contribute to the level database.

• For the user to be able to contribute to a problem, the user needs to solve it beforehand.
  • The user's problem solve states will be merged across the judges. It means that if solved.ac #14640 = BOJ #14640 = Kattis scenery = QOJ #2774, and if the user had solved a problem from any source, the user can contribute to the problem solved.ac #14640.
  • This will negin to mix the contributors across multiple judges.

From this stage, the users will also be rated by the solved.ac rating scheme.

Step III: Strong Integration

These were the integrated before with the BOJ and will definitely make the user experience far more pleasant if supported by foreign OJs:

• The OJs would send the users' submission results in real time;
• The OJs would send informations about new problems, modified problems, rejudges, new users, and deleted users, in real time;
• The OJs would support displaying the problem levels and tags from solved.ac;
• solved.ac and the OJ would work together to support logging in to solved.ac with other OJ's accounts (OAuth, which can also be done in step II)

Step IV: Stronger Integration?

It will be more than awesome tom maybe even support making submissions from solved.ac but with the user's own account in the respective judges. But I am expecting this would happen in the time very far from now.

Requirements

The judges' behavior should be similar to that of the judging environment of the ICPC.

The Protocol

For step III to be done, solved.ac needs to prepare a protocol or maybe a API scheme. I expect this to be done in mid-to-late 2026.

Moderations, I18n, etc

I'll try to think of the other specific topics. In the meantime please feel free to leave a suggestion in the issues.