DMOPC '21 October Contest

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

The contest organizers this time are 4fecta and Riolku.

Once again, the contest authors will not be announced until the end of the contest.

UPDATE: Thanks for writing the contest! The contest authors this time were 4fecta, Riolku, and zhouzixiang2004.

Thanks to Nils_Emmenegger, dxke02, 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 October 12th), 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.
  • 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.


  • 15
    4fecta  commented on Oct. 11, 2021, 10:37 p.m.

    Hi everyone, unfortunately the DMOJ site experienced some downtime from around October 11, 4:18pm to October 11, 5:45pm EST. During this time period, either the site was inaccessible or the judges were unavailable. If any contestant affected by this downtime wishes to be unrated from the contest, they may do so by sending an email to [email protected]. We apologize for the inconvenience, and hope you still enjoy the contest (and Thanksgiving Day).

  • 8
    Snowfall  commented on Oct. 11, 2021, 9:13 p.m.

    judges down :(

  • 0
    qiao_yun20060930  commented on Oct. 11, 2021, 4:38 p.m.

    what are -9999 means in some of the contests

    • 0
      andy_zhu23  commented on Oct. 11, 2021, 6:54 p.m. edited

      "It means that you have been suspected of cheating on a contest. If you believe that this judgement has been made in error, you are encouraged to email us at contact -at- or join the Discord."

  • 14
    Plasmatic  commented on Oct. 4, 2021, 2:20 p.m.

    Depression speedrun any%

  • 11
    Badmode  commented on Oct. 4, 2021, 1:21 a.m.

    Once again, the contest authors will not be announced until the end of the contest.

    Why? I would like to know

    • 18
      EpicChadGamer  commented on Oct. 4, 2021, 4:07 a.m.

      Mid-contest death threats

      • 15
        Badmode  commented on Oct. 4, 2021, 4:59 a.m. edited

        If a specific problem was indeed cancerous, then they're just delaying the inevitable

  • -68
    dxke02  commented on Oct. 4, 2021, 12:08 a.m. edit 2

    This comment is hidden due to too much negative feedback. Show it anyway.

  • 18
    Victor_Chan  commented on Oct. 3, 2021, 10:27 p.m.

    enter image description here