ko_osaga's blog

By ko_osaga, history, 2 months ago, In English

Final Results are out! Congratulations to everyone, especially:

  • orzdevinwang for the first place
  • Adam_GS for the second place
  • kes0716 for the first place in Korea (decided to be Gold at the very last minute!)

IOI 2024 is held in Alexandria, Egypt. Good luck to all participants! I'm also attending as a student coach (Guest) as well; please say hi if you see me!

All times are in UTC+3 (Egypt — Eastern European Summer Time).

  • Day 1: 2024.09.03 09:00 — 14:00
  • Day 2: 2024.09.05 09:00 — 14:00
  • Closing Ceremony: 2024.09.06 19:00 — 21:00

Links

Please, keep all discussions civil and according to the IOI Code of Conduct. Please.

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2 months ago, # |
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Why "Please" twice what happened

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On the Codeforces mirror, how does the submission for problem B work?

UDP: Nevermind, I figured it out. Just implement the functions in the problem statement.

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However,I think orzdevinwang will AK IOI!!!

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hi! I can't see you but I want to, where are you/what are you planning to do today?

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    2 months ago, # ^ |
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    I'll be in the translation session, so not much window today. I'm likely around in the closing ceremony.

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There is no problem statement for any of the problems at ioi.codeforces.com IOI 2024 day 1 (the link above), I only see the input and output.

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Here are the 100-point codes for all Day 1 problems — I wrote them while waiting for the bus to AASTMT :)

Shoutout to dillon0108 for sharing his beautiful solution of Message. Absolute legend.

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    2 months ago, # ^ |
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    In the last iteration of the loop at line 42 in tree, UB is invoked as W[W.size()] is accessed.

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    2 months ago, # ^ |
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    Are there any "easy" solution for Niles? I can't find an approach to it that isn't related to DSU (and requires some mild-heavy casework)

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      2 months ago, # ^ |
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      The other solutions involve segment tree or set or similar stuff the require more case work than DSU.

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        2 months ago, # ^ |
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        Still can't understand how this problem even have 82 AC....... this is definitely harder than IOI22's Fish, around as difficult as Digital Circuit, definitely harder than Closing Time, yet the AC amount says otherwise........ (Still can't find a way to code the DSU without bruteforcing the 16 cases when merging 2 components though

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          2 months ago, # ^ |
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          I can see how this problem has 82 ACs.

          Spoiler
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            2 months ago, # ^ |
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            I can't think of anything lower than the 16 cases corresponding to the connected state of the first and last 2 elements. What are the stored states for each component in the "proper" dsu solution?

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              2 months ago, # ^ |
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              Spoiler
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      2 months ago, # ^ |
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      After sorting by W, say for each D, we can group (i, i-1), or (i, i-2) depending on the contrast <=D. TC of each D is O(n), but u can sort those distance i.e (i,i-1), (i,i-2), and E[i]. Then iterate and set a position to 1-> maintain the maximum sum of a[i]-b[i] that you currently can group. use segment tree of continuous positions that have been set. The merging should be just casework

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    2 months ago, # ^ |
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    I feel quite surprised that the solution of message does not involve any kind of randomness :)

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      2 months ago, # ^ |
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      Should it require ANY kind of randomness, we'll have another Magic Show again......inan international contest. You know how well that went — clever bit manipulation, DSU and 250 lines of intricate code? Nope, 15 lines of CRT it is!

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      2 months ago, # ^ |
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      Since the grader is adaptive, any solution with randomness will be highly likely to be wrong

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    2 months ago, # ^ |
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    Can you explain the logic behind the tree problem?

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      2 months ago, # ^ |
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      Hint (sort of)
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        2 months ago, # ^ |
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        Is there any better way to reformulate the problem in a way that makes subtask 2,3 easier to approach? I'm cpmpletely lost on that here

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      2 months ago, # ^ |
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      Hint
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    2 months ago, # ^ |
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    in how much time you solved them?(an estimate)

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      2 months ago, # ^ |
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      For day 1, I used about 2 hours to come up with 283 pts solution. Then I just read solution to the messages one. It took about 60-90 min to write them.

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    2 months ago, # ^ |
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    Hi, for Nile I think the 3x3 matrix solution is really cool. I'd like to ask: can this be extended to more general recurrence relations? It seems to me that because of the way you are calculating the matrix multiplication: $$$ret.A[i][k] = min(A[i][j] + m.A[j][k], ret.A[i][k])$$$;

    You can only use this for recurrences of type $$$dp[i] = min(dp[i — 1] + C_1 , dp[i — 2] + C_2, ...)$$$ where $$$C_1$$$, ... are constants. Is it possible to extend this technique for more general linear recurrence relations such as: $$$dp[i] = min(A_1 * dp[i — 1] + C_1, A_2 * dp[i — 2] + C_2, ...) $$$?

    Thank you!

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      2 months ago, # ^ |
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      Unfortunately, I'm not aware of an approach for $$$A_i \neq 1$$$.

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For message, did anyone end up using the return value of send_packet? Seems to me like it was just a red herring ...

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    2 months ago, # ^ |
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    Not a contestant, but I found a way to improve the 70 packet solution (4 packets to send 4 bits to locate a good position, 31 to send the whole C on that position while using remaining 15 to send the message, then just send the message) to a 69 packet solution using it:

    First, let P be the message S followed by one 1 and some zeroes so it's length is 1025. We're sending P to avoid sending the length of S directly. Call a position in C good if it's not controlled by Cleopatra.

    As Aisha, find a good position with index 0-15, and call it X. First 3 messages, send 1 bit each message (by sending all 1s or all 0s) to send three bits of X. Now, Bob knows X is one of some two positions from 0-15. Call the other one Y. Next 30 messages, Aisha sends 30 bits of C at position X, skipping X itself (which has to be 0), while sending P on remaining good positions.

    Now, construct array C_X and C_Y, which represent "how would C look if X/Y had the role of X". Basma knows these, but not which is which. If C_Y has a different amount of 1s than 15, Basma knows C_X is C, so Aisha can start using all 16 bits to send P. Otherwise, let A be the smallest position that has a 0 both in C_X and C_Y. Now, use A to send the remaining bit of X, while sending P elsewhere. Now Basma knows X, and therefore C_X, and therefore C, so Aisha can start sending P on all 16 good bits.

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It legal for join IOI by doing TST in many country same time? I make new account for ask this, seem like MYS3 join Malaysia TST and Singapore NOI. For NOI, go round 2. This maybe mean they take spot from someone in SG who can go IOI, that not legal? I send email to organizer but they no reply, so this only way to tell people. What do now? Legal or no? Cheater at IOI?

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    2 months ago, # ^ |
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    I'm pretty sure it depends on the selection criteria for each country. I know that Indonesia team selection can technically have someone from outside Indonesia participating if they go to certain schools but in practice no one has ever even qualified to Indonesia TST from that route.

    I don't think it would be considered cheating at all. A lot of people in Malaysia and Indonesia go to school in Singapore and through some weird coincidence could qualify for both TSTs.

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      2 months ago, # ^ |
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      On another hand, we also got William Lin who got banned from being a representative for Taiwan, as he was studying in an American school, and the Taiwanese delegates apparently only accepts students from pure-Taiwanese schools to "display the superiority of Taiwanese education", which then forced him to get in the USA team. We all know how that ended

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Live 2 day watch party / unofficial commentary https://www.twitch.tv/errichto & https://www.youtube.com/errichto2/live

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orzdevinwang AK IOI!!!

Congratulation!!!

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Zhou Kangyang AK IOI!

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5fa65199fb661110ac0a66c66f62578d.jpeg

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orzdevinwang has AKed IOI!!!!! Congratulation!!!!

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Even though Day 2 did not go his way but he did well in the end. Congrats kshitij_sodani on winning Gold.

Also congrats to orzdevinwang on winning IOI 2024.

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orzdevinwang has AKed IOI!

Congratulation!

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Average Score Per Country

Click
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    2 months ago, # ^ |
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    We have rank 7 in the average score but rank 20 in the medal ranking (which we send to our government) sadness...

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Let's see how long until people pointed out which task is similar to which existing task :)

(For those in the GA meeting, no spoilers! :) )

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Three girls are getting gold medals this year. This must be a record. Are there any statistics about this?

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Are you around after the closing ceremony? The vietnam team wants a picture with you XD.

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Story (actually rant) on Day1C - mild spoiler
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    2 months ago, # ^ |
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    Also on P3: Are there any suspicion from 1 of the 5 AC contestants being Indonesian (the same as the author's)?

    I also think that IOI23's problemset is generally really awesome — literally 0 remotely "bad" tasks, all with interesting concepts (especially Soccer, what kind of demon thought of that thing, utterly beautiful; and Robot, which is.......probably the best IOI task up to date),......and then there's Mosaic, which I can hardly believe is 100% new. At least it's nowhere nearly bad enough to the point of being another Wiring incident (or, even worse, yet another final-touches-to-task-"Game"-was-finished-half-an-hour-before-day-2 moment).

    By the way, what's the expected difficulty of the tasks, sorted by chronological order? Mosaic < Nile < Tree < Riddle < Hiegraphs < Message?

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      2 months ago, # ^ |
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      wow, that is indeed very suspicious

      Mathew Allan did badly on every other task other than those his country set and is also only Master rating (I know there are several people with high performances being only master, but it indeed adds suspicion)

      Niles can probably be explained since it was an easy task, Tree on the other hand....

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      2 months ago, # ^ |
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      I think better evidence should be provided to make an accusation of such kind.

      I don't have an expected difficulty data from the ISC (if they have one). I guess I will mostly agree with the # of solutions for that.

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        2 months ago, # ^ |
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        i mean they are certainly quite suspicious circumstances, you can check his performance....

        Sure, its not proof. Nobody claimed it so.

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          2 months ago, # ^ |
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          I however think that some kind of "home advantage" happens in general (even in non-suspicious way).

          It can be explained by the following mechanism:

          1. Most IOI participants practices for National OI to qualify for IOI.
          2. The National OI may contain a lot of problems with the same task author from the country/region.
          3. There may be a "tendency" of the problem by task author.
          4. If one practice many problem with certain "tendency", one may be good at such problems.
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            2 months ago, # ^ |
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            I understand that home advantage exists. But, do take a look at the difficulties too.

            Tree had only 5 solves and was one of the hardest tasks... looking at the other tasks other than nile and tree, he barely had a bronze level performance, but in this he had a top 5 performance?

            In my mind, I am 100% sure he cheated. I am also 95% sure nothing can be done about it...

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              2 months ago, # ^ |
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              Honestly I see where you're coming from, cause I definitely messed up my day two (spent too long on a fake solve for hieroglyphs, so didn't have much time to solve the others).

              I'd like to clarify that I didn't cheat. I also didn't expect the number of solves for tree to be that bad. My solution was an extension of the Wi<=1 subtask and if you looked at the timeline I actually solved it with a lot of submissions.

              And to the "only master" thing, I was IM before, but dropped a lot when I did a contest abroad.

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              2 months ago, # ^ |
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              Someone can solve a hard problem sometimes and not solve easy problems.

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              2 months ago, # ^ |
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              This is a serious claim. You cannot publicly accuse others of cheating with little to no evidence.

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      2 months ago, # ^ |
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      Well it's not unreasonable that someone just outperformed himself on that one particular day, or someone did particularly poorly on another day, especially considering how brutal day 2 was. I don't think it's fair to draw any correlation or suspicioun between the task author and 1 out of 5 solve.

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On P4's unusual difficulty, it really seems like the one-liner questions are the difficult ones.

Any idea on why the scores are so low, though (Not that the task is any easy, or I can do better than 3pts, for all that matter). Once again, totally surprised that "Given 2 sequence A and B, determine if every common subsequence of A and B is a subsequence of LCS(A,B)" hasn't been given yet (and actually seems to be a very difficult thing). (but, then, again, IOI18's Meetings is nowhere near trivial)

....Again, I'd still wish that IOI discussion threads can (at least) have some short writeup on the solution for every tasks, the way it used to be in 2016-2019

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I think this paper solves a generalized version of UCS in $$$O(nm)$$$ time.

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    Research paper problem (literally). Wow.

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    In case I'm not hallucinating: Is subtask 4 of UCS......literally asking for the LCS of 2 sequence in O(NlogN)?

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      2 months ago, # ^ |
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      no....you can use properties of UCS to figure out when there can't be a UCS, otherwise the string is no longer a general string

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Chinese participants scores reduced and one disqualified?

https://stats.ioinformatics.org/results/2024

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    2 months ago, # ^ |
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    One Chinese was disqualified. Two had half of their points taken away for the second day. Caught with cell phones

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    2 months ago, # ^ |
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    sphinx: Even though you figured out all the colors, there is another way to get only 50% of the points for the subtasks

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      2 months ago, # ^ |
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      What was the policy regarding cell phones and the likes in general? How do the ISC/HSC check for students' devices? Just asking, as I'm generally interested in the organization of IOIs, and it seems like a strange thing that such a devastating blow to the Chinese team could've happened

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        2 months ago, # ^ |
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        I took part in IOI 2022 and 2023. Phones are definitely forbidden in the contest hall. However, IOI generally works on an honor system, and they don't actually check people for phones, etc.

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        2 months ago, # ^ |
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        In IOI 2023 Indonesia team was told to keep our phones with our LO before entering the contest hall. If I'm not mistaken either our one of our delegation leaders/part of our delegation asked about this. In last year's IOI we were not allowed to take anything in the contest hall (food, mice, keyboards, pens, etc). At least I didn't see anyone bringing a bag into the contest hall.

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      2 months ago, # ^ |
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      ....the joke flew over my head entirely. Wow.

      (Not to be mean-spirited, but as a joke: Wow, the Chinese are so innovative, figuring out an entirely different solution from the ISC!)

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      2 months ago, # ^ |
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      Furthermore: Has this happened before? Should this affect China's trustworthyness in past contests (especially IOI20-21-22, those that were taken online)? Is the ISC/IC working on trying to prevent things like this from happening again?

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        2 months ago, # ^ |
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        As a former member of the Chinese team, I'm confident that none of my fellow students would attempt to cheat during the IOI.

        This year, I heard it was the leader's first time serving as an onsite leader. In Chinese national contests, participants typically turn off their phones, place them in their bags, and leave the bags by the wall in the contest room. Without closely reviewing the rules, the leader assumed the procedure would be the same and didn’t instruct the students to remove their phones. As a result, three students unknowingly brought their phones into the contest. The only student who didn’t bring a phone had left it charging at the hotel after it ran out of battery.

        I don't know why one student carried the phone with him instead of putting it in the bag. I understand that's suspicious. But I tend to think it's unintentional.

        [UPD: I heard that the night before IOI, the leader will leave the students. In that case, it would be the guide's responsibility to ask the students to handle their phones. I apologize for my misunderstanding. ]

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          2 months ago, # ^ |
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          Isn't there video footage that can vouch for the 2 with the phones in their bags?Also where they caught by a check or did they casually take their phones out?

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          2 months ago, # ^ |
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          That's sad :(

          To add, does someone know why there is no quarantine anymore?

          I've heard that at the IOI 2019 team guides used to take participants' phones, so that there's little way to cheat (and current situation cannot happen). Also, at this or previous IChO quarantine took place, maybe at other olympiads too

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            2 months ago, # ^ |
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            I heard some talk that they dont do quarantines because currently there are so many eletronic devices that just taking away phones is not enough to prevent communication between setters and participants.

            Also, what would actually prevent this from happening is better communication. When i went to my IOIs (2022 and 2023) knowing what we should do with our phones was a mess. Should we leave them with the guide? At the hotel room? With the team leaders? It felt like every day the answer was different. I imagine communication was similarly lacking this IOI.

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            2 months ago, # ^ |
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            In IOI 2023 I really thought that the guides (or whoever) would take our phones in the day before the contest day at like afternoon or something. They didn't and we just handed our phones to our guide right before we enter the contest space.

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          2 months ago, # ^ |
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          I don't suspect the 2 participants who put their phone inside the bag, turned off. But it is very suspicious that one went to the toilet with their phone on them, turned on, don't you think?

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            2 months ago, # ^ |
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            I agree. It’s suspicious indeed. The conditional probability p(turning on the phone + carry it to the toilet | not cheating) is low. However, my (personal) prior probability of cheating is also low; if we apply Bayesian rules, I can’t tell for sure.

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      2 months ago, # ^ |
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      I must say, this day two 50% cheating penalty must be one of the weirdest rulings that I've ever seen. Did they come up with this penalty on the spot or is this actually part of the IOI rules?

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        2 months ago, # ^ |
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        Agreed

        I dont like such half measures...take one of the 2 actions.

        If you think what they did amounts to cheating, diaqualify/void day 2. If you dont think so, any action is illegitimate.

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          2 months ago, # ^ |
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          There were three choices given by IC:

          1. 1 DQ and 2 half score.
          2. 3 DQs.
          3. 4 DQs.

          and the first choice was elected by a unanimous vote.

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            2 months ago, # ^ |
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            So why did IC didn't consider to DQ only 1 participant who had all means to use phone.

            According to testimony above, It seems all others had it turned off and reasonable inaccessible, and while I agree that protocols should be followed, I think the students have no blame in the accident, and it should be attributed to local organizing committee

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              2 months ago, # ^ |
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              The two other guys got their phone "with them, but switch off and in their bags" — I think this means that the phones are still quite accessible?

              Also, I think that there should be some sort of penalty to make guides and contestants more cautious regarding this problem.

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              2 months ago, # ^ |
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              Because the rules clearly said "Any attempts to bring any other items unlisted into the competition rooms are considered cheating." Below is more detailed explanation:

              According to the IOI's calendar and related rules, participants should leave their mobile phones to their coach for most of the time because coach can get the full problemset several hours earlier to discuss and translate the statement. So the communication between coaches and participants is illegal at this time.

              Btw it's so weird that they only checked CHN participants bags. I think checking all is fairer.

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                2 months ago, # ^ |
                  Vote: I like it +23 Vote: I do not like it

                Btw it's so weird that they only checked CHN participants bags. I think checking all is fairer.

                While there probably were such people, I personally don't know anyone who'd bring bag to contest hall, because I've thought it's a common sense you can't do that at ioi? So, well checking all would rather mean specifically looking for 5-10 who could also possibly have bags which, i guess, wasn't a solution in the after-contest mess.

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                2 months ago, # ^ |
                  Vote: I like it 0 Vote: I do not like it

                While I think this is a good way to go about it, it may break the player's mind and not be conducive to a fair game.

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            2 months ago, # ^ |
              Vote: I like it +200 Vote: I do not like it

            Why was 4 DQs even an option, from the moment the contestants enter the hall their team doesn't matter.

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            2 months ago, # ^ |
            Rev. 2   Vote: I like it +104 Vote: I do not like it

            That is incorrect.

            I will first point out that according to IOI Contest Rules, mobile phones are explicitly prohibited and having one in the competition room is considered cheating.

            IC has considered the case anonymously (only one voting member who was part of investigation was aware of the identity of contestants or country in question and the rest were not told) and after long deliberations IC has decided on disqualification of one contestant and 50% score reduction in Day 2 for the other two contestants.

            This was then presented to the General Assembly who need to ratify IOI results according to Regulations. Although I cannot say currently with 100% certainty, but from my memory the ratification was unanimous in GA.

            At no point IC has presented to GA any other options.

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              2 months ago, # ^ |
              Rev. 2   Vote: I like it +5 Vote: I do not like it

              I heard this from some CHN people on site. Sorry if incorrect :(

              But I think, for it was unanimous, so IC didn't need extra discussions or sth.

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            2 months ago, # ^ |
            Rev. 3   Vote: I like it +43 Vote: I do not like it

            I attended the GA and can confirm that this is false. IC only presented their non-unanimous decision for 1 DQ and 2 half score. Of course the GA can argue about it, but surprisingly(?) there was not much argument.

            I am certain there was no point where 3 DQs or 4 DQs were even mentioned by any IC or GA members.

            The IC mentioned that they internally deliberated this issue for 1.5h before reaching the decision. So it's possible that the options you mentioned were on their table. We have to wait for the IC meeting minutes (if this topic will be included in their minutes).

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        2 months ago, # ^ |
          Vote: I like it +5 Vote: I do not like it

        they 100% came up with this penalty on the spot

        upvoted

        as a Chinese myself I support DQ 1 or DQ 3 but not this one

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      2 months ago, # ^ |
        Vote: I like it +43 Vote: I do not like it

      Y, Z 50% reduction sounds harsh to me...

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    2 months ago, # ^ |
      Vote: I like it +41 Vote: I do not like it

    Since MagicalFlower got a silver medal, does that mean that he can possibly participate next year?

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      2 months ago, # ^ |
        Vote: I like it +27 Vote: I do not like it

      China has a rule that every participant can participate in IOI at most once. So while he might still be eligible, he won't be able to represent China the next year.

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        2 months ago, # ^ |
          Vote: I like it +34 Vote: I do not like it

        I thought that you can't participate again only if you win a gold medal...

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          2 months ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Oh, I see. I wasn't aware of that. Thanks!

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            2 months ago, # ^ |
              Vote: I like it +64 Vote: I do not like it

            You need to be qualified to China National Training Team to compete for National Team. Huang doesn’t participate in NOI this year(actually participated unofficially), so he is unable to participate in IOI again imo

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              2 months ago, # ^ |
                Vote: I like it +5 Vote: I do not like it

              It seems that he was confident in getting gold medals. How unlucky.

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                2 months ago, # ^ |
                  Vote: I like it +13 Vote: I do not like it

                He (and the other two besides orzdevinwang) just graduated from high school, thus not qualified for IOI according to rules in China.

                China only allows participating in the summer after grade 11(in the case of orzdevinwang) and after grade 12(in the case of the other three) for the full selection process lasts two years and candidate must be in high school(Grade 10~12) during the whole process.

                The rule evenvalue mention is that if you got gold medal in Grade 11, you won't be eligible for the next. (Literally you can attend again if you got silver or lower, but no one did so for recent years)

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                  2 months ago, # ^ |
                    Vote: I like it 0 Vote: I do not like it

                  oh, I forgot the age limit. Thanks for reminding me.

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2 months ago, # |
  Vote: I like it +47 Vote: I do not like it

Congratulations to Esomer for first gold medal in Spain history!

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2 months ago, # |
Rev. 4   Vote: I like it +41 Vote: I do not like it

My recollection on what happened on day 2 translation night. This should appear in IOI 2024 GA meeting minutes as well (which will only be released next year after IOI 2025 GA approves it).

First major objection
Second major objection
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    2 months ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    I believe that when we think about "submitting a problem for IOI", there is an assumption about the lower bound of the difficulty (as we fear that everyone can solve the problem that we purpose), and hence the lack of easy problems.

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      2 months ago, # ^ |
        Vote: I like it -23 Vote: I do not like it

      No need to worry about that, though, as we can always have yet another Fountain Parks incident again. While the model solution sounds almost silly and obvious the moment one sees it, it's still the hardest problem in IOI21, and gamegame's solution to it was literally "calculate some flows, merging components, ridiculously intricate DFS" and the likes, so......there particularly doesn't exist a problem that someone won't choke on (unless it was Cluedo or Memory or POI, in which case not solving them is just genuine 300cf behavior)

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        2 months ago, # ^ |
          Vote: I like it +20 Vote: I do not like it
        • I believe that Fountain Parks is not intended to be the easiest problem on IOI21. Also, I see that you oversimplified the solution — good luck trying to solve the problem using your summarization of "literally "calculate some flows, merging components, ridiculously intricate DFS" and the likes"

        • I also think that we care about number of solves in general, if there are 150-200+ solves and some people choke then it is their problem. If no one chokes on a problem and everyone solves it, then what is the point of the problem anyway?

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          2 months ago, # ^ |
            Vote: I like it -23 Vote: I do not like it

          I didn't. gamegame did. It was literally his way to the solution (or, at least, what he decided to post on Codeforces). This is to say that: Regardless of the author's intended simple solution, contestants can and will manage to come up with their own ways to make the problem more challenging/less challenging than it was.

          If anything, the IOI tasks should be used as grounds for popularizing some highly efficient techniques (DSU tree/Alien Trick) OR grounds for improving on previous solutions (in fact, within the 9 months between the task submission deadline of IOI23 and IOI23 Day 2, noone even thought that Z = 5 for Robot Contest was possible.....and it was). Giving "easy" problems to people who are expecting the equivalent of 3k5+ Codeforces problems IS grounds for some LGM to come up with the next revolutionary algorithm or something.....so there's precisely zero penalty on submitting things you'd thought to be trivial.

          (Finally, on gamegame's solution, I kid you not, this was the monstrosity he thought up. If you REALLY thought that I was trying to say "yeah, the problem was trivial, his solution was just these simple things, bro!" instead of "This problem was intended to be the easiest task of IOI21 by the ISC, with a hilariously simple one-liner construction, yet some LGMs managed to come up with some absolute witchery 400-lines solution, so there's particularly no guarantee that people would NOT overestimate the difficulty of each tasks, no need to worry"........ignoring that I wrote a massive "hardest problem" right over there........you should definitely get your reading comprehension checked. No kidding)

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            2 months ago, # ^ |
              Vote: I like it 0 Vote: I do not like it

            Ey my bad on that "also" part. But I still believe that it is not supposed to be the easiest problem in the contest, just saying.

            To your first comment: I don't think anyone thought that Fountain Parks was easy (including the author), and it didn't turn out to be an easy problem. I don't see any "incident" here.

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          2 months ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          From what I remember as a participant, Parks was intended to be the easiest problem on IOI 2021 Day 1. Obviously, this ended up not being the case, but it was a large factor in why DNA was used on Day 2.

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            2 months ago, # ^ |
              Vote: I like it 0 Vote: I do not like it

            Oh, so that's why the ISC decided to use the nerfed version of DNA (which is already easy enough as is) in day 2. Wow. never considered that

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2 months ago, # |
  Vote: I like it +15 Vote: I do not like it
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2 months ago, # |
  Vote: I like it +81 Vote: I do not like it

I don't think blindly halving the scores without being able to determine if the Chinese players are cheating or not is a convincing approach, I think we should give an accurate conclusion on whether they are cheating or not, cheating directly removes the scores, and obviously nothing should be done if they aren't cheating, and that should be what we all look forward to, not the vague results we have today!

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    2 months ago, # ^ |
    Rev. 2   Vote: I like it +40 Vote: I do not like it

    you are right. there wasn't any camera in the contest hall? I guess we can figure out everything when we check it

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    2 months ago, # ^ |
      Vote: I like it -19 Vote: I do not like it

    Unfortunately, not allowing mobile phones is an official ban, which is very reasonable, because the coach or team leader will get the question earlier than the player to discuss the translation related matters, so the player should disconnect the Internet before the game, otherwise he may cheat before the game, which is also the reason for the ban.

    Since the CN team has violated it, cheating or not, this is an official red line.

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      2 months ago, # ^ |
        Vote: I like it +3 Vote: I do not like it

      I think quarantine/disconnecting only the leader is more reasonable/convenient than disconnecting all the players, in order to prevent the leaking of the problems.

      Of course, you also need to hand out the phones during the contest, but it is not related to problem leak anymore.

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    2 months ago, # ^ |
      Vote: I like it +60 Vote: I do not like it

    They had their phones with them, which is already cheating at that point. No ambiguity.

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    2 months ago, # ^ |
      Vote: I like it +35 Vote: I do not like it

    I think the issue here never was we have evidence if they cheated. Even if we know 100% they did not use their phones during the contest, bringing the phones itself is already against the rules. There are two parts in the IOI rules:

    "Any attempts to bring any other items unlisted above into the competition rooms are considered cheating" and later, "Violating any of the following rules is considered cheating, and may result in disqualification"

    Given this info, we know that the IC has the right to disqualify the two participants, but since the word "may" is used, they can decide on a lighter penalty.

    To me it's similar to the law, where it states the maximum punishment for a crime is $X fine or Y years of jail, but the judge may choose to give a lighter punishment depending on the scenario. Of course we can discuss whether 50% is justified or not, but I'd argue this 50% is not meant to be a vague answer of "idk if they cheated", but what the IC judged to be an appropriate penalty of breaking the bringing of phone rule.

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2 months ago, # |
  Vote: I like it +91 Vote: I do not like it

As a Chinese OIer,I believe the innocence of the two participants having their Day2 points halved is not in doubt.However this is indeed a violation of the clearly-written rules, and it just doesn't make sense not to penalize, even if the blame should be placed on the irresponsibility of the team leader.

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    2 months ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    I think some of the blame should also be put on the organizer as well for even allowing contestants to bring any items into the contest hall. Last year my team was told before hand that we were not allowed to bring anything and the rule was enforced during the contest days to avoid confusion.

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      2 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      its stated on the website that the team leaders are responsible for ensuring that their teams follow the rules. I think that's a terrible rule, but it is stated, so it's their fault sadly

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2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

When I heard the latest news, I couldn't believe it

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2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

how to solve sphinx ?

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    2 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it
    3 points
    7 points
    21 points
    33 points

    Idk how to fetch remaining 36 points.

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    2 months ago, # ^ |
      Vote: I like it +36 Vote: I do not like it
    50% Solution
    Full Solution

    Some extra thoughts

    Spoiler
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2 months ago, # |
  Vote: I like it +26 Vote: I do not like it

I have a problem regarding the incident of Chinese team: Did they come up with their plan of halving the Day 2 score of Kubic and MagicalFlower just on the spot? What's the point of neither just DQ them nor having their rankings unchanged?

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    2 months ago, # ^ |
      Vote: I like it +23 Vote: I do not like it

    I think there is a point, since realistically it will be easier to convince the Chinese team compared to 3 DQ, which is what the rule states.

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2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Did they not announce the IOI 2025 dates in the closing ceremony?

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2 months ago, # |
  Vote: I like it +194 Vote: I do not like it

So the two chinese participants who got their points halved had phones found in their bags turned off. Did the committee check the bags only of the chinese team or all of the bags in the contest hall? I believe there were lots of participants who naturally put phones in their bags (with intention to leave the bags somewhere outside and have an easy access to them right after the contest) and accidentally brought the bags into the contest area due to unstrict rules. It would be strange to have exactly one team bringing their bags to the contest hall (and it accidentally appeared to be the chinese team). If the committee made a more thorough search and found phones in bags of like half of participants, would they penalize all of them?

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    2 months ago, # ^ |
    Rev. 2   Vote: I like it -55 Vote: I do not like it

    If you caught one team member carrying a turned on phone, it's natural that you should check all of their team members. They are possibly the ones who were communicating with that team member. Doing so doesn't imply that you are obliged to check every 300+ participants in spite of resource and time limitation.

    It's not possible to predict answer on your hypothetical scenario. A case with 3 people had already gone through extensive discussion. The assumed scenario is rather disastrous and would need even more discussion.

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      2 months ago, # ^ |
        Vote: I like it +84 Vote: I do not like it

      Is "there would have to be more discussion with others and it would be a disaster" a valid sole reason not to do the right thing, assuming that checking everyone's bag (thus enforcing the rules for everyone) instead of only one team is a right thing?

      Also, I would assume that checking the bags must happen before participants enter the contest floor (since they allow bags at all, which is also not what I'm used to)

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        2 months ago, # ^ |
          Vote: I like it -56 Vote: I do not like it

        Read my comment again, "there would have to be more discussion with others and it would be a disaster", so: "It's not possible to predict answer".

        It's weird that you assume that checking all 300+ bags are the only right thing to do after the incident. These 4 phones must be checked. If there is a murder mystery will you ask everyone in the city for fairness? Where do you draw a line?

        And then, I don't have a good sense on how the onsite security checks were processed. Probably it wasn't too good, as we have this incident. What I only know is that electronic devices are strictly prohibited in the contest hall.

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          2 months ago, # ^ |
            Vote: I like it +63 Vote: I do not like it

          I don't understand your murder mystery analogy. So if someone is killed on the contest floor, you will not want to check all participants?

          Electronic devices may be prohibited, but the rules delivery system is obviously flawed to say the least -- I don't remember reading any rules when I was a high schooler. Like, I knew that I mustn't use my phone. It didn't imply that I just leave it anywhere. Sometimes we were forced to give the phone to our team leader before the tour, sometimes we were forced to leave it with the organising committee, sometimes we probably didn't even leave it anywhere -- I was never bothered with any of these and always assumed that my only responsibility is to take care of defending the honour of my country on the contest floor and not the "switched off/left outside" choices

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            2 months ago, # ^ |
              Vote: I like it -54 Vote: I do not like it

            Whatever that helps. You encountered a possible cheating incident. Big question is if he cheated and whom he did with. You must check 3 phones of other team members to answer it. Then you may want to check other 300+ bag, possibly because you are obsessed with whatever fairness metric or you just have a lot of energy. You do you, you are fortunately not my policeman.

            And then this complaints on the delivery system seems weird because you are obviously not a contestant. Electronic devices are strictly prohibited in the contest hall. If your intuition contradicts it, well, good luck.

            (I'll try to not answer the possible upcoming replies)

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              2 months ago, # ^ |
                Vote: I like it +34 Vote: I do not like it

              I was a contestant in IOI2023

              We didnt know what to do with our phones either. At the last moment, we left it with our guide.

              I would not assume we are allowed to take them into the contest hall but if bags are allowed, surely phones within the bags are allowed right? Bags shouldnt be allowed but they were for some reason....which is the weirdest part

              There definitely is an issue with how rules are communicated.

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        2 months ago, # ^ |
          Vote: I like it +94 Vote: I do not like it

        It seems that bags... aren't allowed?

        from https://www.ioi2024.eg/contest-rules

        Which makes all of this even weirder — why didn't anyone warn the contestants about the bags when they entered the contest hall?

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          2 months ago, # ^ |
            Vote: I like it +3 Vote: I do not like it

          This is so weird. There are so much talking about whether to check the bags, when to check the bags, and whose bags to check.

          But the bags are not permitted in the first place!

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          2 months ago, # ^ |
          Rev. 2   Vote: I like it -12 Vote: I do not like it

          +1 on this. Our team members took everything without bags. Just weird talks

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          2 months ago, # ^ |
          Rev. 2   Vote: I like it +37 Vote: I do not like it

          This

          Seems like bad mamagement and pushing the mistakes onto the contestants....

          eduardische can you tell how bags were allowed? It seems very natural to me to assume if bags are allowed, you can keep the phones in the bags (otherwise what even is the purpose of allowing bags) segtree template within the bag would be fine?

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            2 months ago, # ^ |
              Vote: I like it +9 Vote: I do not like it

            I’m speaking my personal thoughts now.

            Ultimately, it is delegation responsibility to fully understand contest rules:

            Delegation Leaders have the responsibility to ensure that all members of their delegation fully understand these rules and abide by them.

            Bags are not allowed, although not explicitly. It was a surprise to learn that they were allowed on the contest floor. IC will work closely with the future hosts to ensure that this does not happen again. As the result, no action was taken because someone brought their bag. Mobile phones are explicitly prohibited however. But, given that it is possible to just accidentally forget the phone in the big bag, this resulted in different sanction for two of the contestants.

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              2 months ago, # ^ |
                Vote: I like it 0 Vote: I do not like it

              Were all other participants checked for phones within bags? It seems a very understandable error to me....

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                2 months ago, # ^ |
                  Vote: I like it +3 Vote: I do not like it

                I was not part of the investigation, but from what I’ve been told, the main focus of the investigation was the concrete violation reported to relevant committees. During this process, it was deemed necessary to speak with entirety of delegation. At that time, the competition has ended so there was no possibility to search every bag on the contest floor.

                So while it is possible that there were other violations of the contest rules, I personally don’t believe that it should prevent IC sanctioning known violations. On a personal note, as a past contestant, I am really surprised from this thread that there are a lot of contestants that are not personally familiar with contest rules that dictate what is and what is not allowed. That is not a risk I personally afforded when I was competing.

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    2 months ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    I think for fairness the committee should check all the bags. Just hope that in the future the committee can remind the participants of the rules and don't let the tragedy happen again

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    2 months ago, # ^ |
    Rev. 2   Vote: I like it -30 Vote: I do not like it

    Come on, guys! We all know that thank to the punishment given to Chinese team, Korean get a gold. Stop downvoting Ko_osaga, he's doing his best for his nation!

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      2 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Please abide by the IOI Code of Conduct. Insulting other teams' delegation, especially contestants, doesn't seem like doing your best for your nation.

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2 months ago, # |
  Vote: I like it +1 Vote: I do not like it

orzdevinwang get 600 points in ioi2024!

He all kill ioi!

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2 months ago, # |
Rev. 2   Vote: I like it +27 Vote: I do not like it

Congratulations to orzdevinwang for AK IOI. However,I was in the same high school as him and I graduated three years earlier than him (But I haven't participated in any OI contest). Have to feel the difference between people's talent,hope you can create more miracles in the near future!

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2 months ago, # |
  Vote: I like it +11 Vote: I do not like it

Can anyone tell me about what did the Chinese contestants do on day 1. If on day 1, they had taken their phones to the contest zone, then the penalty should be applied for the points of that day also. If they had not taken their phones on day 1, then why did they take it on day 2.

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    2 months ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    The organizers probably didn't check their bags on day 1.

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2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Any updates on IOI2025's timeframe and host for IOI27?

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    2 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Some updates will happen at tomorrow’s General Assembly

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2 months ago, # |
  Vote: I like it -17 Vote: I do not like it

Plot twist: The real reason all Chinese members carry their phone with (except for zhoukangyang) is simply to outright capture the moment Zhou solves all the tasks. I think the ISC was too harsh on them. Justice for China!

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2 months ago, # |
  Vote: I like it +3 Vote: I do not like it

orzdevinwang AK IOI!

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2 months ago, # |
  Vote: I like it +42 Vote: I do not like it

For the first time a Bangladeshi won gold medal in IOI 2024.Soumya1 Feeling happy for him.

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2 months ago, # |
  Vote: I like it +38 Vote: I do not like it

Tasks authors now revealed! https://www.ioi2024.eg/competition-tasks

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    2 months ago, # ^ |
      Vote: I like it -6 Vote: I do not like it

    So the author of Thousand Islands setted UCS, the author of Digital Circuit setted Mosaic (now that I know, Mosaic is actually not stolen, just "similar idea that appeared before").

    Will there be official editorial this year?

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2 months ago, # |
  Vote: I like it +65 Vote: I do not like it

And it was announced that IOI 2027 will be held in Potsdam, Germany. Germany previously hosted IOI in 1992.

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2 months ago, # |
  Vote: I like it -11 Vote: I do not like it

Also huge Congratulations to kshitij_sodani !!

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2 months ago, # |
Rev. 4   Vote: I like it +66 Vote: I do not like it

ASEAN teams at IOI 2024:

Thanks to everyone for joining in the photo. Lets try to get a better one (with proper lighting lol) next time!

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2 months ago, # |
  Vote: I like it +3 Vote: I do not like it

Why do Iranian and Israeli students have asterisk(*) near their place?

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    2 months ago, # ^ |
    Rev. 2   Vote: I like it +15 Vote: I do not like it

    And one German contestant. According to Regulations, everyone who competed remotely (9 contestants) would not count towards calculating medal boundaries but would be inserted into the table and given appropriate awards. The asterisk near rank denotes that as it does result in duplicate ranks, since on IOI Stats I keep ranks identical for medal boundary computations.

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2 months ago, # |
  Vote: I like it 0 Vote: I do not like it

The scoreboard seems to be down (for now). Will there be an archive of the scoreboard similar to the last few years?

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2 months ago, # |
  Vote: I like it +161 Vote: I do not like it

Hello everyone, author of Nile and Tree here! It had been my ultimate goal in competitive programming to author a problem in IOI. It was a bit unfortunate that they settled for one of the most generic titles for one of my problems (Tree) 😂😂 instead of going with my originally proposed title (Xylem). Nonetheless, I'm very grateful to have two problems used in IOI and I hope everyone enjoyed them as much as I did making them!

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    2 months ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    Great! Can you describe your process of coming up with these problems?

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    2 months ago, # ^ |
      Vote: I like it +7 Vote: I do not like it

    on Nile: Another problem with 2 approach. What was your original solution — DSU with merging states, or "Generic segtree where each node stores a 3x3 matrix"

    on Tree: Again, aside from the obvious thing (how did you come up with the "trick" of summing suffixes combining with union by rank).....I still cannot understand how to solve the 0/1 version. Please help.

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2 months ago, # |
  Vote: I like it +36 Vote: I do not like it

Now that dust is settled, I wonder if chinese team explained their side of the story. Was it some confusion that happened in terms of logistics, some failure in communication, a naive mistake made by a novice team leader, or the unlikely case where there was a real attempt to cheat. It must have been very hard for the chinese contestants.

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    2 months ago, # ^ |
      Vote: I like it -47 Vote: I do not like it

    They are most likely cheaters. That would explain why they get the best results every single year.

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    2 months ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    https://new.qq.com/rain/a/20240907A01O6M00

    According to the circulated information—

    During the second round of IOI 2024, participant X was carrying a powered-on phone in their pants pocket. While X was in the restroom, a volunteer noticed the phone in their pocket and reported the matter to the IC (International Committee) for handling.

    Upon learning of the incident, the IC, along with the volunteer, inspected the participant's phone. Since the phone was turned on, the IC requested Participant X to unlock the phone for inspection. After the inspection, the IC confiscated the phone but allowed the participant to continue the competition normally.

    After the competition ended, the IC informed the head of the Chinese team of the situation, prompting the head to inspect the other three Chinese team members. Ultimately, all four members of the Chinese team were found to have carried backpacks into the exam hall, with the backpacks placed directly beside their seats. Additionally, two other participants, Y and Z, were found to have a powered-off phone inside their backpacks. According to the IOI Contest Rules, the IC explained that any attempt to bring electronic devices with computing or communication capabilities is considered cheating, and the matter would be discussed internally for resolution.

    I used ChatGPT to translate the above paragraph, which is quoted from the article linked above.

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2 months ago, # |
  Vote: I like it +24 Vote: I do not like it

Are the solutions published anywhere?

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2 months ago, # |
  Vote: I like it +83 Vote: I do not like it

How to solve Hieroglyphs?

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    6 weeks ago, # ^ |
    Rev. 3   Vote: I like it +66 Vote: I do not like it
    Definitions
    Part of subtask 2
    Subtask 4
    Subtask 5
    Observation 1
    Observation 2
    Full task