DMOPC '21 September Contest

Welcome to the first DMOJ Monthly Open Programming Competition of the 2021-2022 season!

The contest organizers this time are Riolku and 4fecta.

To add an extra layer of mystery, the contest authors will not be announced.

Thanks to Aaeria, Nils_Emmenegger, WilliamWu277, and Zeyu for testing and feedback on problems.

This round will be rated for all participants.

Before the contest date, you may wish to check out the tips and help pages.

This contest will consist of 6 problems, the difficulty of which may range anywhere from CCC Junior to CCO level.

You will have 3 hours to complete the contest. After the contest window begins, you may begin at any time. Once you enter the contest, your personal timer will start counting down and you will be able to submit until 3 hours from when you started, or until the hard deadline (00:00:00 EDT of September 7th), whichever comes first.

After joining the contest, you proceed to the Problems tab to begin.

Here are the parameters of the contest:

  • Some problems offer partial marks in the form of subtasks.
  • Unlike previous DMOPCs, ties will be broken by the maximum submission time that increased score with no penalties.
  • A maximum of 50 submissions will be allowed per problem.
  • Scoreboard will be hidden, until your window is over. Divulging the contents of the scoreboard to participants who have not finished their window is an offense, the punishments of which are listed below.
  • Problems will be approximately increasing in difficulty, and will all have full feedback. Reading all of the statements is recommended.
  • Checkers: unless otherwise specified, identical. The contest will follow the standard convention of having all lines terminate in a \n character, with no trailing whitespace.
  • Rated for opening the contest. Being able to read the problems will cause the contest to be rated.
  • It is guaranteed that all the problems will be solvable with C++, and all time limits will be at least 2x the runtime of the reference solution.

We have listed below some advice as well as contest strategies:

  • Remove all extra debugging code and/or input prompts from your code before submitting. The judge is very strict — most of the time, it requires your output to match exactly.
  • Do not pause program execution at the end. The judging process is automated. You should use stdin / stdout to perform input / output, respectively.
  • Python users are recommended to use PyPy 2/3 over Python 2/3 when submitting.

Clarification requests for the contest must be routed through the clarification system provided on DMOJ, and not through other channels including but not limited to Discord and Slack. Furthermore, all clarification requests will be handled the way they normally are in IOI. Note that, in particular, clarification requests must come in the form of yes/no questions.

Due to rampant issues with cheating on contests that has happened recently, any suspicious behavior during the contest window may result in your rating being impacted negatively. Such behavior includes, but is not limited to:

  • Divulging the contents of the scoreboard to participants who have not finished their window.
  • Registering for the contest with at least two accounts.
  • Participating in the contest with an account that is not your primary account.
  • During the contest window, talking about the contest in more detail than answering a yes/no question about whether one participated in the contest. This includes, but is not limited to, posting spoilers about the contest and public speculation of the contest.
  • Attempting to exploit bugs in the platform to subvert the constraints of the contest.

Punishments may include performance being unrated or, for more serious infractions, being forcibly ranked at the bottom of the scoreboard.

At the end of the contest, you may comment below to appeal a judging verdict. In the case of appeals, the decision(s) of DMOJ staff is final.


  • 7
    Riolku  commented on Sept. 7, 2021, 12:13 a.m.

    Because of an issue with P3 interactor feedback, comment below or email [email protected] to request an unrate. You can also use the Slack or Discord.

  • 7
    4fecta  commented on Sept. 4, 2021, 4:01 p.m.

    Due to popular request, we have decided to extend the contest window by 24 hours.

    • 5
      wleung_bvg  commented on Sept. 4, 2021, 4:27 p.m. edited

      Recently the DMOJ staff decided that it was a good idea to extend the DMOPC '21 September Contest to end on September 7th instead of September 6th. They claim that this was a popular request; however, there were only 5 known people who requested for an extension. This behaviour has become more common recently on DMOJ and needs to come to an end. If this continues to happen, DMOJ users will expect contests to always be extended, which should not be the case. It is very difficult for problem setters to have to constantly monitor the contest for tickets to answer, and the number of users participating does not increase significantly based on prior DMOJ contest history.

      Signing this petition indicates that you support moving the DMOPC '21 September Contest end date back to September 6th at midnight, as well as putting an end to the practice of extending contests simply because a few users want it extended.

      Sign here:

      • 8
        Riolku  commented on Sept. 4, 2021, 7:57 p.m.

        This petition is an unecessarily agressive way of asking for a change in DMOJ's policies. As it happens, DMOJ contests will not be extended during the window any more.

        • 13
          Tony1234  commented on Sept. 4, 2021, 8:46 p.m.

          since when has a petition been considered agressive

  • 17
    Plasmatic  commented on Sept. 2, 2021, 1:19 p.m.

    wish everyone high rating :)

    • -1
      ryanawad  commented on Sept. 4, 2021, 1:04 p.m.

      wholesome dmoj moment

    • -121
      AQT  commented on Sept. 3, 2021, 5:21 p.m. edited

      This comment is hidden due to too much negative feedback. Click here to view it.

      • -10
        vishnus  commented on Sept. 3, 2021, 8:26 p.m.

        This comment is hidden due to too much negative feedback. Click here to view it.

      • 13
        kevinyang  commented on Sept. 3, 2021, 7:09 p.m.

        ok soohotiam

    • 7
      MCSDA  commented on Sept. 2, 2021, 3:29 p.m.

      I wish I could get that...

      • 20
        piddddgy  commented on Sept. 3, 2021, 4:24 p.m.

        Don't get too caught up in noisy indicators like rating, just enjoy solving problems :)

        • 1
          dchoo333  commented on Sept. 5, 2021, 3:09 a.m.

          piddddgy speaks words of wisdom.

  • 10
    Lost  commented on Sept. 2, 2021, 8:44 a.m.

    Everyone's favorite contest DMOPC is back for the start of the school year!

  • 11
    Tony1234  commented on Aug. 30, 2021, 9:47 a.m.