DMOPC '19 December Contest

Welcome to the fourth DMOJ Monthly Open Programming Competition of the 2019-2020 season!

The problem writers this time are george_chen, KevinWan, little_prince, c, tankibuds, and richardzhang.

Please note that this contest will be full feedback.

This round will be rated for all participants who submit at least once.

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

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

This contest will feature a 7-th problem (Problem 0) for students who are just getting started with programming.

Some problems offer partial marks in the form of subtasks. If you cannot solve a problem fully, we encourage you to go for these partial marks.

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 (23:59:00 EST of Dec. 31st), whichever comes first.

After joining the contest, you proceed to the Problems tab to begin. You can also go to Users if you wish to see the rankings.

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

  • Ties will be broken by the last submission time that increased your score plus penalties. The first submission time of your highest score will be used.
  • Each non-AC (excluding Compiler Errors) submission will incur a penalty of 5 minutes.
  • It is not guaranteed that the problems will be in order of increasing difficulty. Reading all of the statements is recommended.
  • 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.
  • It is guaranteed that all the problems will be solvable with C++.

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 Slack and Discord.

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:

  • 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.


  • 6
    TheEpicCowOfLife  commented on April 15, 2020, 7:20 p.m.

  • 8
    Korjwist  commented on Jan. 12, 2020, 4:01 p.m. edit 3

    Are the contestants allowed to search things up during the contest window? Also for anyone who did CCC, are we able to search things up, too? Sorry about the beginner questions...

    • 8
      4fecta  commented on Jan. 12, 2020, 5:27 p.m. edited

      You are only allowed to search up official documentation of the languages you are using. Anything else is a bannable offense on both the DMOPC and CCC.

      Edit: You are allowed to search things up on the DMOPC, as the rules do not officially state against it. However, please do not get into the habit of doing it, as it is considered cheating on the CCC.

      • 30
        zxyl  commented on Jan. 12, 2020, 6:24 p.m.

        That is not a bannable offence on DMOPC.

      • 10
        p1geon  commented on Jan. 12, 2020, 6:08 p.m.

        geeks for geeks is official documentation don't @ me

      • 3
        Korjwist  commented on Jan. 12, 2020, 5:47 p.m.

        So... only through this?

        • 5
          richardzhang  commented on Jan. 12, 2020, 9:19 p.m.

          Okay, just to clarify this, it's fine to look up algorithms and general idea pages (like Codeforces blogs), but it is not okay to copy code, share specifics, or even discuss about a DMOPC online while the contest is still officially ongoing. This contest has already ended, so you're free to use whatever resources you'd like :)) (outside of directly copy-pasting someone else's code, of course)

          • 3
            Korjwist  commented on Jan. 12, 2020, 9:30 p.m.

            Alright. Thx so much :)

  • 8
    richardzhang  commented on Jan. 9, 2020, 1:40 p.m.

    Okay, with much thanks to Riolku, problems 0 to 3 now have editorials! Check them out at your leisure. Problems 4 to 6 may have editorials coming out later, but please don't be too disheartened if they don't come out quickly, as the problem setters still have exams to contend with. (although, if you are willing to contribute an editorial, please contact me on Slack!)

  • 8
    gouh9qn  commented on Jan. 7, 2020, 5:38 p.m.

    when will/are the problems open for solving again?

    • 5
      richardzhang  commented on Jan. 8, 2020, 11:57 p.m.

      All problems have been made public.

      • 3
        gouh9qn  commented on Jan. 9, 2020, 12:25 p.m.

        many thanks : )

      • 21
        Zeyu  commented on Jan. 9, 2020, 12:57 a.m.

        Will there be editorials/solution sketches? Some of these problems are quite interesting (p4 for example)

        • 18
          richardzhang  commented on Jan. 9, 2020, 1:25 a.m.

          Hmm, we don't have any plans in place right now to create editorials (especially since exam season is coming up :blobsweats:), but if there's enough demand (upvotes for comments requesting editorials), we might reconsider :)).

  • 13
    666245  commented on Jan. 1, 2020, 4:54 p.m.

    [user: bobxiong88] you are incredible! please teach me how to type faster :)

  • 5
    daviecar  commented on Dec. 31, 2019, 7:06 p.m.

    I'm requesting to be unrated. Reason is that my internet was wonky throughout the contest which resulted in me being unable to see the problem statements.

    • 3
      tankibuds  commented on Dec. 31, 2019, 10:04 p.m.

      Unfortunately, a wonky internet connection is not sufficient reason to be unrated. Sorry about that.

      • 10
        daviecar  commented on Dec. 31, 2019, 10:34 p.m.

        Okie, that's sad. Thanks for the response though.