Back to School '19

It's that time of the (school) year again, and to celebrate, we present the Back to School '19 contest! Get back into your tip top programming shape and start the school year with a new rating!

The problem setters for this contest are Ninjaclasher, Zeyu, Beautiful_Times, and wleung_bvg.

Special thanks to aeternalis1, Dormi, and insignificant for testing.

Back to School '19 will consist of 8 problems, with difficulty ranging between CCC Junior to IOI level. The contest questions have a wide range of difficulty, and you can get partial marks for partial solutions in the form of subtasks. If you cannot solve a problem fully, we encourage you to go for these partial marks.

Contestants can participate in any 4 hour window between Friday, September 6, 3PM EDT and Sunday, September 8, 11:59PM EDT. Once you enter the contest, you will be able to submit until 4 hours from when you started, or until the hard deadline (September 8, 11:59:59PM EDT), whichever comes first.

This contest will use the pretest/systest format for some of the problems. On problems 5-8, when you submit, you will receive your result on some of the test data, called preliminary tests (pretests). After the contest, we will rejudge all solutions on the complete set of test data, and that will determine your final score. Note that getting AC on pretests does not ensure that you will pass system testing, and that solutions that do not pass pretests will not pass systests. We intend the pretests to be as strong as possible. Despite this, there may still be some edge cases that are not in the pretests. Be sure to check the correctness and complexity of your solutions!

This contest will be rated for contestants with at least one submission.

The parameters that were described above are listed here:

  • Contest duration: 4 hours.
  • Number of problems: 8. The pretest/systest format will be used for problems 5-8. Each problem will be worth 100 points and have subtasks that offer partial credit.
  • Rated for all participants who submit at least once.
  • Scoreboard will be visible.
  • No submission limit.
  • Ties will be broken by the sum of times used to solve the problems starting from the beginning of the contest. The first submission time of your highest score will be used.
  • Checkers for problems: standard.

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.
  • Deliberately obfuscating code.

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

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

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:

  • Start from the beginning. Ties will be broken by the sum of times used to solve the problems starting from the beginning of the contest. The first submission time of your highest score will be used.
  • 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++ and Java.
  • Read carefully, and try to attempt all the problems. They may not be as hard as they seem and you may get partial points!

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


  • 5
    Pookmeister  commented on Sept. 9, 2019, 10:23 p.m. edit 3

    If anyone wishes to contest any aspect of the contests such as claims of cheating, please contact the DMOJ administrative staff on Discord.

  • 7
    1419903188  commented on Sept. 7, 2019, 11:59 a.m.

    Will there be editorials after the contest?

    • 4
      Ninjaclasher  commented on Sept. 7, 2019, 1:19 p.m.

      There are editorials planned, however we will not guarantee that there will be editorials for all the problems.

  • 3
    corgi  commented on Sept. 6, 2019, 5:06 p.m.

    What are the rules regarding the internet? Am I allowed to use the cppreference website?

    • 1
      Ninjaclasher  commented on Sept. 6, 2019, 5:24 p.m.

      You are allowed to use any online and offline resources.

  • 2
    wleung_bvg  commented on Sept. 6, 2019, 3:16 p.m. edit 3

    There is currently an issue regarding the pretest and system test format, as well as the scoreboard. This issue will be resolved in the next few minutes. Anyone who was significantly affected by this may request to be unrated.


    The issues have now been resolved. All submissions have been rejudged.

  • -1
    Chess1000  commented on Aug. 29, 2019, 12:44 p.m.

    I have a question about the systest format. What if I submit a solution that just barely passes/does not pass in time? Several times, in contests, I had a solution that would almost run out of time. If I submit it enough times, it would eventually pass all of the cases. How would we deal with that?

    • 2
      wleung_bvg  commented on Aug. 29, 2019, 1:31 p.m.

      All submissions made during the contest will be run on system tests. Your earliest submission with the highest score will be used in the calculation of your rank. If you have doubts about whether your solution will pass, you should resubmit an optimized version (please don't spam the judge with submissions).

    • 3
      Rimuru  commented on Aug. 29, 2019, 1:12 p.m.

      faster input is the way to go ->

      (scanner is slow af)

      • 14
        c  commented on Aug. 29, 2019, 3:08 p.m.

        Or just use C++ :tm:

  • 26
    slightlyskepticalpotat  commented on Aug. 18, 2019, 1:59 p.m. edited

    Can't drop my rating if I'm not rated ¯\_(ツ)_/¯

  • -14
    Plasmatic  commented on Aug. 17, 2019, 10:09 p.m.

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

    • 16
      Shinichi  commented on Aug. 18, 2019, 12:10 a.m.

      Little do the plebians know, but the admins and fellow elites on this site only make rated contests to decrease our ratings and morale.

      • 4
        Beautiful_Times  commented on Sept. 3, 2019, 9:47 p.m.


        I only set this contest so this contest wouldn't decrease my rating