majk's blog

CEOI 2019 Mirror
By majk, 5 years ago, In English

The 26th Central European Olympiad in Informatics will take place in Bratislava, Slovakia, during July 23rd-29th 2019. The most gifted high school students from 13 countries will have the opportunity to prove their knowledge and skills in informatics.

Codeforces will organise the online mirror for this year's competition. The online mirrors will take place after the finish of each of the 2 competition days, having the same scoring format.

The online mirror schedules are the following:

Contest format

  • The contest will be unrated for all users.
  • You will have to solve 3 tasks in 5 hours.
  • There will be full feedback throughout the entire contest.
  • The scoreboard will be hidden until the end of the contest.
  • The tasks will have partial scoring. The maximum score for each problem will be 100 points.
  • Among multiple submissions only the one that achieves the maximum score is counted towards the final ranking.
  • The submission time does not matter for ranking.
  • There will be enough fun for all colours ranging from newbie to international grandmaster. Legendary grandmasters can spice it up by turning it into a drinking game (ask Radewoosh for details).

Link to onsite contest with official rules and scoreboard

UPDATE: Much nicer scoreboard than on the first day made by arsijo. Many thanks!

Congratulations to all onsite contestants who battled our unusually hard problemset for 10 hours. You can view the final standings.

Many thanks to KAN for running the mirror, MikeMirzayanov for both platforms, all of our authors, testers and the whole CEOI staff and sponsors!

Day 1 mirror:

  1. mnbvmar 300
  2. Benq 300
  3. gamegame 281
  4. ainta 271
  5. Tutis 254

Day 2 mirror:

  1. zx2003 230
  2. saba2000 230
  3. TLE 200
  4. cuizhuyefei 200
  5. panole 200
  6. dacin21 200

Results of both days combined: (https://codeforces.com/spectator/ranklist/e354b9b95c3626a3cfdfdb9eb37a7a6f)

Editorials: day1 day2

  • Vote: I like it
  • +313
  • Vote: I do not like it

Comments Comments (82)
| Write comment?
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Auto comment: topic has been updated by majk (previous revision, new revision, compare).

→ Reply
»
5 years ago, # |
  Vote: I like it +27 Vote: I do not like it

Heads up: the mirror of the second contest overlaps with Facebook Hacker Cup Round 3.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    Funnily enough, this is not the first contest I tried to schedule in conflict with FBHC. Therefore, we move it to Sunday at 08:05 UTC.

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    also the same day we have ,google kickstart round. it will be really good ,if date can be changed but i know its not possible.

    → Reply
»
5 years ago, # |
  Vote: I like it +155 Vote: I do not like it

Radewoosh, please some words about drinking game

→ Reply
»
5 years ago, # |
  Vote: I like it +14 Vote: I do not like it

Radewoosh drinking game is such high iq. From Legendary Grand Master to Drunken Master.

→ Reply
»
5 years ago, # |
  Vote: I like it +3 Vote: I do not like it

Having the scoreboard hidden until the end is an interesting twist.

→ Reply
»
5 years ago, # |
← Rev. 4   Vote: I like it 0 Vote: I do not like it

Where can I find the list of tests used for problems from past contests, if I'm solving the problem after the contest is over? For example if my submission is failing at Test 5, I want to know the data in Test 5 so I can troubleshoot.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    Never mind, found it!

    In case anyone else wants to know, you go on your profile page, and click Submissions, then click on the 8-digit number of your submission in the first column.

    → Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +8 Vote: I do not like it

Can we solve problems and get score if we participate? Or it will be too hard?

Sorry for bad English!

→ Reply
»
5 years ago, # |
  Vote: I like it +28 Vote: I do not like it

So where can we find said scoreboard?

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    Scoreboard

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +11 Vote: I do not like it

      Thanks!

      → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +16 Vote: I do not like it

      One more question: why does Romania use Russian flag in the scoreboard?

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it -24 Vote: I do not like it

        Just a prank bro.

        You should be glad Romania, Czech Republic and Croatia don't have the Hungarian flag and Poland doesn't have a three-way mix.

        → Reply
        • »
          »
          »
          »
          »
          5 years ago, # ^ |
          ← Rev. 2   Vote: I like it +54 Vote: I do not like it

          I don't think this is funny. Contestants represent their countries. I, personally, would be quite offended if someone put another country's flag next to my name.

          → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +13 Vote: I do not like it

    Where is that profile picture from?

    → Reply
»
5 years ago, # |
  Vote: I like it +3 Vote: I do not like it

Do participants at CEOI have hidden scoreboard during the contest too? If no, maybe it would be better to also not hide the scoreboard at mirror contest?

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it -22 Vote: I do not like it

    They shouldn't have a scoreboard, and they shouldn't have internet access either. The mirror contest will have a public scoreboard because it doesn't matter and there's already a public scoreboard.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +2 Vote: I do not like it

      But mirror would also be more interesting without public scoreboard.

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it +20 Vote: I do not like it

        If you prefer it that way, you can simply not look at it during the contest.

        → Reply
»
5 years ago, # |
  Vote: I like it +1 Vote: I do not like it

Could someone tell me what's the difficulty of CEOI?

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +43 Vote: I do not like it

    hard.

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +9 Vote: I do not like it

    normal.

    There are subtasks. Some are hard, some are easy. Some years (like the last 2), nothing is too hard. Other times, like this year, there's something hard and a lot of easy subtasks.

    → Reply
»
5 years ago, # |
  Vote: I like it +3 Vote: I do not like it

Could you also publish the contest material (tests etc.) after each contest day?

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Whether the editorial of problems will be published?

→ Reply
»
5 years ago, # |
  Vote: I like it +35 Vote: I do not like it

Why doesn't each subtask contain each previous subtask which it supersedes? For example, it shouldn't be possible for me to solve subtask 4 and not subtask 3 of A or subtask 2 but not subtask 1 of C. :|

→ Reply
  • »
    »
    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +8 Vote: I do not like it

    Same problem with B, managed to solve subtasks 3,5,6 but not 1,2,4.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      So it's possible to get 100 with the wrong solution by doing some not much good looking ifs.

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        My solution is still based on HLD ;D

        → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Wait a minute, 6 is the full solution, how come you solve it and not solve 1, 2, 4!? I solved 1-4, but not 5-6. 5 is also not hard, but I didn't manage to write it.

      → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I'd also prefer that, but it's not done at CEOI. Maybe to not overkill the kids. Therefore, that's how it is in the mirror too.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      There is no need to tell the participants that this is done. They can assume the tests are copied into all suitable groups.

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it +5 Vote: I do not like it

        It's the truth, so I don't mind.

        → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    It is not always the case that subtask n+1 is the same as subtask n with some additional observations, so the dependencies would have to form a dag and we would need to give you that dag. I am sceptical whether such complication adds anything to the contest. If you managed to get subtask 2 for C but not subtask 1, this sounds more like weak tests then anything else.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +18 Vote: I do not like it

      You can also determine for each test case a subset of subtasks where it belongs to, and this can be done automatically using input validators. I think this is the optimal way to create subtasks in an IOI-style contest.

      → Reply
»
5 years ago, # |
  Vote: I like it +16 Vote: I do not like it

I have participated in an IOI type competition in first time and surprised at the very unusual format of this competition, in which the standings of the participants and the number of solved tasks are not visible. I also habitually tried to solve whole problem

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

How to solve the Dynamic Diameter problem? It looks very interesting.

→ Reply
»
5 years ago, # |
  Vote: I like it +10 Vote: I do not like it

How to solve A ?

→ Reply
»
5 years ago, # |
  Vote: I like it +100 Vote: I do not like it

Where can we see the CF scoreboard for the contest?

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +52 Vote: I do not like it

Where can I see the Final standings of this mirror?

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +30 Vote: I do not like it

    Sorry, I thought it is opened automatically after the end. You can see the standings now.

    → Reply
»
5 years ago, # |
← Rev. 3   Vote: I like it 0 Vote: I do not like it

My solution for A:

Consider all buildings already built and that you are removing them one by one. Let V be number of vertices which are in contact with atleast one building, let E be number of edges which are in contact with atleast one building, now if the graph of building is connected, then Euler's formula for connected planar graphs must hold (here number of faces F = number of buildings + 1). So, you can only erase a building if erasing it will maintain the equality (the graph will remain connected), call such a building available. A building is on the boundary if it is contact with one empty space. Now, maintain a set of all buildings on the boundary which are available, and erase the one with maximum id. Update the set after erasing each building. (Each update will change the status of atmost 8 buildings so this can be done fast).

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    not sure, but seems correct.

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    Why should F be the number of buildings + 1? For example, the case of a 3x3 with a hole in the middle has 8 buildings, 10 faces and is connected.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      I thought those cases would give "NO" output due to some reason. I was wrong. Thanks.

      → Reply
»
5 years ago, # |
  Vote: I like it +32 Vote: I do not like it

Can you please enable viewing other's submissions?

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Vote you up. It seems that this feature is still to-be-done because of the special rule on these CEOI problems that CodeForces has never dealt with.

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it -21 Vote: I do not like it

    Meh, done. Viewing submissions was actually allowed, if you found them elsewhere, it was "viewing of common Status" that was blocked in the admin settings.

    → Reply
»
5 years ago, # |
  Vote: I like it -46 Vote: I do not like it

Anybody knows what happened to xyz111 (Yinzhan Xu) ? I can't see him on the top rated. Did his account get banned ? xyz111 p/s : I am a fan of him. lol ^^

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    Ranking applies only to handles that have participated in at least one contest in the last 6 months.

    → Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +3 Vote: I do not like it

The Ukrainian delegation has prepared unofficial standings. The link is ce.oi.in.ua

UPD. If you don't see flags, please clear your cache.

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

can i see the CF scoreboard for the contest?

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it -27 Vote: I do not like it

    At CEOI are interesting problems, but the bad is that CEOI is all about speed. there are only five hours! It is impossible to solve this hard problems in 5 hours. I time will be more, I am sure I will solve all the problems. Do you agree me?

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +3 Vote: I do not like it

      5 hours is like the maximum reasonable time. The problems are balanced in a way so only some people will be able to solve them in that time frame. Others will get less points.

      → Reply
»
5 years ago, # |
  Vote: I like it +141 Vote: I do not like it

I was a participant on-site. Honestly guys don't join it. It literally was the worst contest i ever saw.

→ Reply
»
5 years ago, # |
  Vote: I like it +62 Vote: I do not like it

Only 8 days left until international olympiad in informatic. This a good challenge before IOI Azerbaijan

→ Reply
»
5 years ago, # |
  Vote: I like it -33 Vote: I do not like it

At CEOI are interesting problems, but the bad is that CEOI is all about speed. there are only five hours! It is impossible to solve this hard problems in 5 hours. I time will be more, I am sure I will solve all the problems.

→ Reply
»
5 years ago, # |
  Vote: I like it -40 Vote: I do not like it

At CEOI are interesting problems, but the bad is that CEOI is all about speed. there are only five hours! It is impossible to solve this hard problems in 5 hours. I time will be more, I am sure I will solve all the problems.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it -29 Vote: I do not like it

    Are you agree to my this think?

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +58 Vote: I do not like it

    Yes, you would solve all the problems if the contest duration was 10 years

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

    It's really anything but speed. If you can't solve these tasks in 5 hours, you can't in 10 years. They should be difficult for people participating at CEOI (top 4 in each country), so you shouldn't complain about their difficulty, nor should I.

    → Reply
»
5 years ago, # |
  Vote: I like it +39 Vote: I do not like it

Standings?

→ Reply
»
5 years ago, # |
  Vote: I like it +32 Vote: I do not like it

Are you going to combine both standings for CF mirrors?(maybe also virtuals too)

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Done, see the link in the post.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +10 Vote: I do not like it

      How did you combine them?

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        KAN would be the right person to answer.

        → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it +22 Vote: I do not like it

        "Spectator ranklists" on ADM. page of any contest. I haven't tested it though, MikeMirzayanov made it for CEOI.

        → Reply
»
5 years ago, # |
  Vote: I like it +16 Vote: I do not like it

Is it possible to check submission running time in such type of contests?

If it's not then it would be great to add such feature.

→ Reply