_kun_'s blog

By _kun_, history, 2 months ago, In English,

Div2A ("Palindrome Dance") was authored by jury members altogether, development: darnley

Div2B ("Skewers") was authored by jury members altogether, development: GlebsHP, Codeforces hardened version: KAN.

Div1A ("Timetable") was authored by Zlobober and _meshanya_, development: kraskevich.

Div1B ("Subway Pursuit") was authored by V--o_o--V, development: alkurmtl

Div1C ("Network Safety") was authored by V--o_o--V, development: achulkov2.

Div1D ("You Are Given a Tree") was authored by GlebsHP, development and codeforces edition _kun_, faster model solution: V--o_o--V.

Div1E ("Summer Oenothera Exhibition") was authored by Zlobober, development by malcolm.

Some editorials are being published, please wait a bit :)

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By _kun_, history, 3 months ago, translation, In English,

Hi everybody!

These days Moscow is conducting the 3rd International Olympiad of Metropolises that is an international competition for high school students from biggest cities and capitals all around the world. One of the disciplines of the competition is informatics. Rounds of the competition were prepared by the jury members invited from St. Petersburg, Minsk, Belgrade and Moscow olympiad scientific committee which you may know by Moscow team Olympiad, Open Olympiad in Informatics and Moscow Olympiad for young students (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469).

Scientific Committee of the olympiad consists of: darnley, Endagorion, Jelena Hadži-Purić, Elena Andreeva, Zlobober, GlebsHP. The problems were developed by kraskevich, ch_egor, _kun_, Schemtschik, GoToCoding, malcolm, akvasha, darnley, alkurmtl, achulkov2, gritukan under the guidance of GlebsHP and Zlobober.

Problems were adapted for codeforces by KAN and _kun_, also thanks for MikeMirzayanov for systems codeforces and polygon, which was used to prepare problems of this olympiad. Also, thanks LHiC and V--o_o--V for testing!

Good luck and high ratings for everybody!

Round will happen on Sep/05/2018 19:35 (Moscow time) and will last for two hours. There will be 5 problems for each division.

P.S. We kindly ask everybody who knows problems of an onsite event not to participate in a round and not to discuss them in public, as this may be a subject for disqualification.

Upd: Editorial was published here!

Aaaand congratulations to winners!

Div1:

  1. Um_nik
  2. 300iq
  3. mcfx
  4. ksun48
  5. FCB1234

Div2:

  1. GSHSIF
  2. Yaroslaff
  3. onjo0127
  4. sturdyplum
  5. LYJabc

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By _kun_, history, 3 months ago, In English,

Thank your for participation!

Problem D2A (New Building) was authored and prepared by burunduk2.

Problem D2B (Badge) was authored and prepared by me, the version in SIS's olympiad contained the version with n ≤ 105.

Problem D1A (Elections), D1B (Hat), D1D (Large Triangle) were authored by achulkov2, with D1A prepared by Schemtschik, D1B by achulkov2 and D1D prepared by achulkov2 and senek_k.

Problem D1C (Sergey's Problem) was authored and prepared by WreckingBall.

Problem D1E (Raining Season) was authored and prepared by izban.

Editorials were written by izban and VArtem

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By _kun_, history, 3 months ago, translation, In English,

Hi!

Summer Informatics School (SIS / LKSH) is a summer school for students in grades 6-10. SIS is focused mainly (but not only) on students participating in the Olympiads in Informatics — from beginners to participants of international competitions. SIS is held in July and August, each of them is visited by about 200 students from all over Russia and abroad. The language of the camp is Russian. Additional information about SIS is posted at lksh.ru

Right now, the August branch of the Summer Computer School is running, and on August 11 the traditional team Olympiad is going to place. I am happy to present a rated round based on it!

The round will be rated for both divisions, will be held in Aug/11/2018 16:35 (Moscow time), in each division there will be 5 tasks and 2 hours to solve them.

The problems of this round and the SIS olympiad were authored and prepared by SIS's teachers: izban, achulkov2, Schemtschik, i_love_isaf27, senek_k, asokol, WreckingBall, burunduk2. Also, I would like to thank Dembel for his help with olympiad's organization.

Thanks to our problems testers: _meshanya_, burunduk2, gritukan, niyaznigmatul, manoprenko!

Thank you, MikeMirzayanov, for the codeforces and polygon systems!

Yes, we are aware, that this contest clashes with ProCon Junior on codechef. However, given the schedule of the SIS and the approaching VK cup finals we can't do anything with it, sorry for that =/

Good luck!

UPD: The round will have one interactive problem for both divisions. Please, read the post about interactive problems here: Interactive Problems: Guide for Participants.

Congratulations to winners!

Div1:

  1. Marcin_smu
  2. Radewoosh
  3. Swistakk
  4. Panole233
  5. ko_osaga

Div2:

  1. Onuz
  2. aurelio
  3. usachevd0
  4. jebouin
  5. etiennerossignol

Upd Thank you for participation! Due to vk-cup conduction rating recalculation will happen slightly later, than usually.

Upd The editorial is published!

You may also check the unofficial editorial, written by neal.

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By _kun_, history, 4 months ago, In English,

D2A author: 300iq, _kun_, developer: 300iq

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D2B author: isaf27, developer: _kun_

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D1A author: isaf27, developer: isaf27

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Jury's solution (isaf27): 40973089

D1B author: 300iq, developer: flyrise

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D1С author: pashka, developer: _kun_

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D1D author: tourist, developers: qoo2p5, VArtem

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The first solution: 40971595 and the second solution: 40971634.

D1E author: isaf27, developer: isaf27

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Jury's solution (by isaf27): 40973023

D1F author: GlebsHP, developers: adrozdova, PavelKunyavskiy

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Credits to all jury members, who contributed to this round and EJOI: tourist, PavelKunyavskiy, niyaznigmatul, 300iq, GlebsHP, pashka, qoo2p5, VArtem, demon1999, flyrise, ifsmirnov, isaf27, yeputons, _kun_.

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By _kun_, history, 4 months ago, In English,

Unfortunately, we had a bug in our interactor of the interactive problem.

The interactor contains the following code:

if (y < x)
    t = -1;
else if(y > x)
    t = 1;
else
    t = 0;
if(!p[q % n])
    t *= -1;
cout << t << "\n" << flush;

This is the opposite to the statement. However, it turns out that this error doesn't causes any harm for solving problem — it actualy just inverts the pattern, selected by judges. This also wasn't noticed during testing, by the same reason — the error is not visible to the user code.

But it may cause unexpected behaviour for hackers -- since they write the pattern themselves.

We are very sorry for this error and decided to do the following:

  • The round will be rated, because very little people (maybe even zero) got affected (the people, who made incorrect hack)
  • If you made a hack, which turned to be incorrect due to the error, we will cancel your  - 50 points and recalculate your rating afterwards. Please PM me if you have such a hack.

We are very sorry again. This is a huge lesson to us to be more attentive.

I hope you enjoyed the round!

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By _kun_, history, 5 months ago, translation, In English,

Hi, codeforces!

I am happy to invite you to the codeforces round #493, which happens at Jul/01/2018 17:05 (Moscow time).

This round writers are — Ildar 300iq Gainullin, Grigory gritukan Reznikov, Mike MikeMirzayanov Mirzayanov, and me, _kun_.

Big thanks for people, who tested round — Shiqing cyand1317 Lyu, Andrew GreenGrape Rayskiy, Ivan isaf27 Safonov, Alexey aleks5d Upirvitsky. Also thanks to Mike MikeMirzayanov Mirzayanov and Nikolay KAN Kalinin for help with round preparation.

And to Mike MikeMirzayanov Mirzayanov for codeforces and polygon systems.

Traditionally, there will be 5 problems for 2 hours. I hope you will enjoy the problemset, good luck and have fun!

Scoring distribution will be published before the round.

UPD: Scoring distribution is as follows:

Div1: 500 1250 1500 2500 3000

Div2: 500 1000 1250 2000 2500

You may also want to check this post for post-contest stream.

UPD2: The editorial was published!

UPD3: Congratulations to winners!

Div1:

  1. fjzzq2002
  2. ksun48
  3. fateice
  4. Swistakk
  5. Um_nik
  6. Petr
  7. V--o_o--V
  8. eds467
  9. LHiC
  10. uwi

Div2:

  1. kirisamejin
  2. liu_runda
  3. AntiLeaf
  4. Kosai
  5. highplay121
  6. st-Firdavs
  7. traxexeuler
  8. paladin
  9. kmyiu
  10. Maxim

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