eduardische's blog

IOI 2020 Day 2 Tasks & Overall Preliminary Results
By eduardische, history, 4 years ago, In English

IOI 2020 preliminary results are now available at IOI Stats. Please note that these results are not yet final and are subject to change.

Day 2 tasks statements are also now available at IOI 2020 website.

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4 years ago, # |
  Vote: I like it +34 Vote: I do not like it

William Lin — we knew you'd win.

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    4 years ago, # ^ |
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    He's now a legend for me, especially considering his background.

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4 years ago, # |
  Vote: I like it +22 Vote: I do not like it

Problem Stations is similar to problem JOI Spring Camp 2016-2017: City. In City we are only given $$$S$$$ and $$$T$$$, and here we also have all neighbors of $$$S$$$. Using the idea from City gets a pretty high score.

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    4 years ago, # ^ |
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    Is that legal? I mean some of the rules for tasks selection at IOI is "1. the tasks should not have been seen by any potential IOI 2020 contestants;" and "2. the tasks should not have been used in any recent similar competition;" (from here: https://ioi2020.sg/call-for-tasks/). Yes, I know is not the same task, but is quite similar.

    Moreover, Stations would give an unjust advantage to the Japanese team over others, since a similar problem appeared at a Japanese training camp.

    Besides that, I found Stations a pretty interesting problem to solve.

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      4 years ago, # ^ |
        Vote: I like it +5 Vote: I do not like it

      The spring camp was three years ago, each spring camp has 12 problems and in the world if you only look at the OI TST problems about a 100 relevant are set. Add to that about a 100 Codeforces problems per year which might be able to appear at IOI, you get about 600 problems. Setting a problem which is not similar to any of those 600 problems is hard, and checking if it is similar to any is even harder. Keep in mind that 600 is only a rough estimate and the number is a lot larger, the OI Checklist contains more than 600 problems, And all of that should be done by a small group of people.

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it +6 Vote: I do not like it

    Are you sure? Since City has a special constraint in tree such as "every vertex can be reached from vertex 0 in at most 18 edges". City is solved using this special constraints.

    Stations is different, there is no such constraints. I agree that 65.32 points can be solved in the idea similar to 22 points in City, but this idea is also a "typical technique", which is used in many problems.

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      4 years ago, # ^ |
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      By similar I didn't mean they are the same problem. I just shared a problem that almost asks the same thing. The constraints make huge differences.

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4 years ago, # |
  Vote: I like it +6 Vote: I do not like it

Will there be pdf-writeups of the solutions?

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4 years ago, # |
  Vote: I like it -23 Vote: I do not like it

Congrats to William! And big shout-out to CHN for taking 4 golds and rk1!

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4 years ago, # |
  Vote: I like it +11 Vote: I do not like it

TAIWAN NUMBA WAN

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4 years ago, # |
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You can solve IOI 2020 tasks here:
https://tlx.toki.id/problems/ioi-2020

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    4 years ago, # ^ |
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    Is there some problem with the servers? I'm having a lot of trouble submitting, and "internal server error" all the time.

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4 years ago, # |
  Vote: I like it +29 Vote: I do not like it

It seems the attached grader in task mushroom computes the score as $$$\frac{220}{Q}$$$ not $$$\frac{226}{Q}$$$. eduardische Endagorion could you please look into this? Or does Endagorion wants everyone to solve this with $$$Q = 220$$$? ( ͡° ͜ʖ ͡°)

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    4 years ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    I do believe the grader at the contest calculated the correct score, the score I got was the one I roughly expected according to the formula. I also think other contestants would have noticed it as well.

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      4 years ago, # ^ |
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      I think the grader on the website is different with the contest ones?

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    4 years ago, # ^ |
      Vote: I like it +21 Vote: I do not like it

    Problem mushroom was created by AngusRitossa not Endagorion

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    4 years ago, # ^ |
    ← Rev. 3   Vote: I like it +24 Vote: I do not like it

    The ISC can confirm that the grader at the contest calculates using the correct formula. The error in the IOI 2020 website is caused by a local change of the grader during the contest for some experimental purposes. This local change is never uploaded to the contest CMS. It seems like we forgot to revert the change before uploading the grader to the IOI 2020 website at the end of the contest.

    The website is maintained by the host, and they are aware of the mistake and currently working on fixing this. Thanks ko_osaga for reporting this, and sorry for the inconvenience.

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      4 years ago, # ^ |
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      If solutions exist for 220 queries, why limit the queries to 226?

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        4 years ago, # ^ |
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        I am not implying a 220 queries solution exists. The reason for the experimental local change is not an existence of a 220 queries solution.

        Personally, I am not aware of a 220 queries solution.

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    4 years ago, # ^ |
      Vote: I like it +23 Vote: I do not like it

    Seems to be a mistake. But I mean, go ahead and make my day. =)

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4 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Does anyone know if physical medals will be distributed this year?

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