NercNews's blog

By NercNews, 4 years ago, translation, In English

Hello friends!

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ICPCLive broadcast

Standings

Problems

This weekend we'll hold two large-scale final stages of important Championships in the region: ICPC Northern Eurasia Finals 2019 and Russia Open High School Team Programming Contest.

Competitions are traditionally held at several places: in St. Petersburg, Barnaul, Almaty, Tbilisi and Kremenchuk. School teams will fight for the "Champions of Russia" Cup. Student teams will meet in a serious intellectual fight for places to the ICPC 2020 World Finals, which will be held on June 25 in Moscow. This is going to be the third final organized in our region.

Of course, join ICPCLive broadcasts for live-streaming from both events. Live streams are expected from the opening of the championship, both contests, and closing ceremonies.

UPD: Congratulations to teams of ICPC 2020 finalists!

  • SPb SU: 25 (Belichenko, Bykov, Petrov)
  • Nizhny Novgorod SU: Almost Retired (Daniliuk, Kalinin, Ryabchikova)
  • MIPT: Godnotent (Belykh, Golovanov, Sergunin)
  • SPb ITMO: 1 Standard deviation (Budin, Kirillov, Sayutin)
  • Innopolis: 1 (Gaivoronskiy, Khakimiyon, Yalalov)
  • HSE: Logarifmya4ka (Anoprenko, Romanov, Safonov)
  • Belarusian SU: #1 (Dubovik, Karabeinikau, Kernazhytski)
  • Latvia: 2 (Civkulis, Zajakins, Zajakins)
  • Moscow SU: NoNames (Chunaev, Kalendarov, Koshelev)
  • SPb HSE: Last Hope (Bogomolov, Labutin, Podguzov)
  • Saratov SU: 1 (Meshcheryakov, Petrov, Piklyaev)
  • Belarusian NTU: #1: Great team (Sheftelevich, Vasileuski, Zdanovich)
  • Kazan FU: 2 (Ilikayev, Kapralov, Yagafarov)
  • Yerevan SU: One Last Dance (Galstyan, Muradyan, Mikaelyan)
  • International IT University: 2 (Kuanyshbay, Niyazbekov, Khlinovskiy)
  • Belarusian SUIR: #2 (Shavel, Udovin, Vishneuski)

ROHSTPC

269 teams were invited to participate in the final stage of the competition. 128 of them will meet in Saint Petersburg in the historical park "Russia — is my history". 49 teams will compete in Barnaul, 56 teams — in Almaty and 18 teams will take part in the competition in Tbilisi and Kremenchuk.

The main round of the championship will begin this Saturday (30 November) at 10:00. As the tour starts, we'll add links for you to monitor results.

Some teams that have high chances of becoming Cup winners are listed in the table below:

Team City Participant 1 Participant 2 Participant 3 Rating
Power of Three St.Petersburg Ефремов Андрей
receed
Гайнуллин Ильдар
300iq
Одинцов Андрей
forestryks
8110
Mex Foundation Moscow Лифарь Егор
Egor.Lifar
Савкин Семён
cookiedoth
Шеховцов Александр
Jatana
7657
Graneli Tbilisi Birkadze Nika
saba2000
Toloraia Teimuraz
Temotoloraia
Basadzishvili Archil
achi_basadzishvili
7271
а) Moscow Ушаков Фёдор
----------
Федосеев Тимофей
fedoseev.timofey
Пискалов Дмитрий
TheWayISteppedOutTheCar
7189
Ого! Кажетсья это $#@! Moscow Логинов Игорь
IgorI
Шуклин Максим
xoxo
Садовничий Антон
sadovan
7092
Преимущественно овощи Kazan Миннахметов Булат
Minnakhmetov
Харисов Булат
Nutella3000
Исмагилов Азат
ismagilov.code
6912

More teams with their total ratings you can see in the post. Thank you very much, ismagilov.code!

Northern Eurasia Finals

Student competitions will start this Sunday, December 1 at 9:30(Moscow time) at four sites: the historical Park in St. Petersburg, the Altai state technical University in Barnaul, the Georgian University of Business and Technology in Tbilisi and the Kazakh-British Technical University in Almaty.

Links to the results table, as well as the tasks of the contest will be provided soon after the start of the main round of the competition.

If you don't plan to participate in the semifinals, you can try your hand at the challenges of the Northern Eurasia finals in the mirror.

We're going to follow the teams and tell you about the news! Note that the results of this contest dictates which teams will be selected to represent the North Eurasia Region on World Finals ICPC 2020.

Some teams with their total ratings, which we're going to follow especially closely listed in a table below:

Team Participant 1 Participant 2 Participant 3 Rating
SPb ITMO: 1 Standard deviation Николай Будин
budalnik
Дмитрий Саютин
cdkrot
Арсений Кириллов
craborac
8122
MIPT: Godnotent Александр Голованов
Golovanov399
Евгений Белых
WHITE2302
Андрей Сергунин
AndreySergunin
8032
Moscow IPT: Fennecs Дмитрий Григорьев
gop2024
Николай Третьяков
ShadowLight
Денис Шпаковский
Denisson
7938
NN SU: Almost Retired Алексей Данилюк
Um_nik
Николай Калинин
KAN
Валерия Рябчикова
Ekler
7759
"Belarusian SU: Belarusian SU #1" Егор Дубовик
244mhq
Александр Керножицкий
gepardo
Федор Коробейников
Mediocrity
7607
HSE: Logarifmya4ka Владимир Романов
voidmax
Михаил Анопренко
manoprenko
Иван Сафонов
isaf27
7562
SPb SU: Havka — ne papstvo Егор Горбачев
peltorator
Михаил Иванов
orz
Савелий Григорьев
sava-cska
7438
SPb SU 25 Дмитрий Беличенко
Dmitriy.Belichenko
Никита Быков
anta.baka
Семен Петров
Semenar
7369
SPb SU: LOUD Enough Никита Гаевой
nikgaevoy
Иван Бочков
tranquility
Владислав Макаров
Kaban-5
7075

Share with us your news, impressions, and photos with hashtags #NEF and #ВКОШП.

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4 years ago, # |
  Vote: I like it -59 Vote: I do not like it

People who don't understand Russian:

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    4 years ago, # ^ |
      Vote: I like it +178 Vote: I do not like it

    People who don't understand Russian:

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4 years ago, # |
  Vote: I like it +17 Vote: I do not like it

So long, not even in English and on the main page.

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4 years ago, # |
  Vote: I like it -81 Vote: I do not like it

Is it only me or NEF = New English File?

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4 years ago, # |
  Vote: I like it +74 Vote: I do not like it

Wow, didn't expect Um_nik and KAN are still eligible for ICPC!

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    4 years ago, # ^ |
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    That's why they're "almost retired". It's the last year when then they can take part in ICPC I guess.

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      4 years ago, # ^ |
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      :( It's also my last year.

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      4 years ago, # ^ |
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      That's true for me, but KAN would be eligible for one more year if he would stay in university next year (at least that's how I understood him).

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        4 years ago, # ^ |
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        Aren't you certain finalists in 2019-2020? If yes, KAN will run out of his attempts to participate in ICPC, so he will retire inevitably.

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4 years ago, # |
  Vote: I like it +41 Vote: I do not like it

VKOShP Standing, ICPCLive. Somehow top 3 teams are badly stuck in first 2 hours...

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

300iq IS THE GREATEST

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4 years ago, # |
  Vote: I like it +28 Vote: I do not like it
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4 years ago, # |
  Vote: I like it +16 Vote: I do not like it

How many people will advance to the WF in this ICPC contest?

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4 years ago, # |
  Vote: I like it +8 Vote: I do not like it

How to solve G,H? Is there editorial?

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    4 years ago, # ^ |
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      4 years ago, # ^ |
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      The optimal strategy is to never random after buying any relic for its price.

      Proof?

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        4 years ago, # ^ |
        Rev. 2   Vote: I like it +34 Vote: I do not like it

        Reduce the cost of each relic by $$$x/2$$$, and add the total cost by $$$n*x/2$$$ in the end. Also change the random price to $$$x/2$$$ and no refund is given, this is the same problem and it becomes obvious that we should never random after buying.

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          4 years ago, # ^ |
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          After reading your comment I realised that we don't need to subtract $$$x/2$$$ and the proof is actually straightforward: we compare $$$s/k$$$ and $$$x + (n - k)/k \cdot x/2$$$. Let's multiply everything by $$$k$$$. Now we have $$$s$$$ and $$$(n + k) \cdot x/2$$$. When we buy any element the first value decreases by some $$$c_i$$$ and the second value decreases by $$$x/2$$$ which is less than any $$$c_i$$$. So if the first value is smaller for some set, it will also be smaller for all its subsets and we can use induction.

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    4 years ago, # ^ |
      Vote: I like it +18 Vote: I do not like it

    G: I wrote subset dp and noticed that if the average of remaining elements is smaller than the current cost of buying a random element then we buy everything with $$$c_i$$$, otherwise we buy a random element.

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      4 years ago, # ^ |
        Vote: I like it +8 Vote: I do not like it

      How to write without precision error? I got WA12, so I thought the assumption is wrong (indeed it is when $$$c_i < x$$$) but it turns out long double wasn’t precise enough.

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        4 years ago, # ^ |
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        For each subset of $$$k$$$ elements with sum $$$s$$$ you should add to answer $$$\min(s/k, x + (n - k)/k \cdot x/2) \cdot \binom{n}{k}^{-1}$$$. You calculate the number of subsets for each $$$k$$$ and $$$s$$$ with knapsack. This way you don't need any subtractions.

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          4 years ago, # ^ |
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          Wow thanks. My formula needed to compute knapsack without one element (so I needed subtract).

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      4 years ago, # ^ |
      Rev. 3   Vote: I like it +8 Vote: I do not like it

      For G, I tried the following, but I can't see why it's wrong. If we're buying, we should buy the cheapest remaining element, because buying a random element costs the same irrespective of the actual costs of the elements.

      Therefore, sort the costs, and do a dp where $$$f(l, k)$$$ is the cost for the suffix starting at position $$$l$$$ if $$$k$$$ elements from the suffix (chosen uniformly at random) were already removed.

      We can either roll and go to $$$(k, l +1)$$$ for cost of choosing randomly or "try" to buy element $$$l$$$: if it was removed already then we go to $$$(l+1, k-1)$$$ for free, otherwise we pay $$$c_l$$$ and go to $$$(l+1, k)$$$.

      Submission: 66292244

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        4 years ago, # ^ |
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        For the same dp state it can be optimal to either buy the cheapest or random element depending on which random elements you already bought.

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          4 years ago, # ^ |
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          Ah, I see. Whether we should buy $$$l$$$ can depend on whether we have $$$l + 1$$$ already. Thanks!

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      4 years ago, # ^ |
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      I am curious to know how you had this observation. Did you stress-test on random tests ? Also when you do decide that you should write a brute-force solution and look for patterns ?

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      4 years ago, # ^ |
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      Anyone has some proof for this ? The editorialists just expect us to come up with it somehow. Although it intuitively makes sense a proof would be nice.

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

how to solve problem K (key Storage) ?

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    4 years ago, # ^ |
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    Compute the fingerprint. The answer is the number of permutations having $$$f_i\leq i \land f_n\neq0$$$. This can be computed with DP or by simple combinatorial logic (Multiply by the number of positions — number of used positions) (Divide by the number of duplicate permutations) don't forget to subtract permutations having $$$f_n=0$$$.

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4 years ago, # |
  Vote: I like it +41 Vote: I do not like it

aid is mad

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4 years ago, # |
  Vote: I like it -51 Vote: I do not like it

orz Havka — ne papstvo

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4 years ago, # |
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Can somebody please explain in more detail the solution for A, please.

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4 years ago, # |
  Vote: I like it +47 Vote: I do not like it

Would you mind updating the ghost standings in the codeforces mirror to the unfrozen onsite standings? Thank you! : )

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3 years ago, # |
  Vote: I like it -10 Vote: I do not like it

How to implement the checker of problem H?

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

Why does my problem D get "Denial of judgement"?

Test: #26, time: 0 ms., memory: 0 KB, exit code: 0, checker exit code: 0, verdict: CRASHED
Checker Log
Unable to find classes\devopsGenerateServerCopieskt.class 

Maybe something goes wrong with the checker?