isaf27's blog

By isaf27, history, 5 months ago, In English

Hello Codeforces.

I'm writing this post to make comments about a situation on the last Codeforces Round and tell the bad news. We did many mistakes and due to them, the round caused much dissatisfaction from the Codeforces community.

Some of our mistakes:

  1. Some stupid mistakes in the statements.

  2. In the problem D2E/D1C the numbers $$$d_i$$$ were not necessarily sorted, but there were no pretests for that.

  3. The checker of the problem D2F/D1D didn't check one of the requirements and due to that $$$8$$$ solutions failed on pretests during the system testing.

  4. After the editorial was posted the mistake was found in the main solution of the problem D1E (more details here). Now we don't know the correct solution.

So, the round was very unsuccessful, I'm very sorry about this. I will make conclusions and will try to avoid such situations later. Please, treat with respect to the authors, even in such a bad situation, a big work was done and I hope you enjoyed the problems.

Now about the bad news: due to the wrong checker and the wrong solution, we decided to make Div1 round unrated, Div2 round is still rated, Sorry for all, who had a big positive rating change.

Also, we are making a D1E problem-solving challenge: if you have an algorithm, that can be proven, please share your approach.

So, that was all news, sorry again,

Ivan.

P.S.

If you are angry now, you can use this post to set a dislike, please don't dislike an announcement/editorial.

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By isaf27, history, 6 months ago, In English

The problems A, C, D, G are authored and prepared by isaf27.

The problems B, E, F are authored and prepared by 300iq.

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Jury solution: link

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Let's discuss your ideas and solutions in the comments. Thanks for your participation!

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By isaf27, 16 months ago, translation, In English
Tutorial is loading...

Jury solution: 54047380

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Jury solution: 54047416
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Jury solution: 54047456
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Jury solution: 54047487
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Jury solution: 54047513
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Jury solution: 54047561
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Jury solution: 54047626
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Jury solution: 54047665

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By isaf27, 16 months ago, translation, In English

Hello, Codeforces!

I'm glad to invite you to Codeforces Round #559 (Div. 1) and Codeforces Round #559 (Div. 2), which will be held on May/12/2019 17:35 (Moscow time). The round will be rated for both divisions (I hope).

All problems were written and prepared by me. Thanks to aleks5d, TLE, sunset, Sooke, Peltorator for testing problems and good advice, 300iq for round coordination and help with preparation and MikeMirzayanov for great systems Codeforces and Polygon.

You will be given 6 problems in both divisions and 2 hours to solve them. Please, read all the problems. Good luck, have fun and I wish everyone high ratings!

The scoring distribution will be announced closer to the beginning of the round.

UPD

The contest finished, contgratulations to the winners:

Div1:

  1. mnbvmar
  2. ecnerwala
  3. ainta
  4. ksun48
  5. ekzhang

Div2:

  1. hbi1998
  2. Nutella3000
  3. calabash_fool
  4. ahgus89
  5. 1207koo

Editorial

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By isaf27, history, 21 month(s) ago, In English

Hello everyone!

I would like to invite you to participate in HackerEarth December Circuits '18. It's a long contest that will start on December 21, 21:00 IST (check your timezone). The contest will run for 9 days.

The participants will be challenged with 7 traditional algorithmic tasks of varying difficulty levels and 1 approximate problem for a duration of 9 days. For traditional algorithmic tasks, you will receive points for every test case your solution passes — so you can get some points with partial solutions as well. For the approximation task, your score depends on the best solution in the contest so far. Here is the detailed timeline of the challenge,

  • Day — 0 Problem 1, Problem 2, Problem 3 (Approximate)
  • Day — 1 Problem 4, Problem 5
  • Day — 4 Problem 6, Problem 7
  • Day — 6 Problem 8
  • Day — 9 Challenge ends

As usual, there will be some nice prizes for the top five competitors:

  1. $100 Amazon gift card + HE t-shirt.
  2. $75 Amazon gift card + HE t-shirt.
  3. $50 Amazon gift card + HE t-shirt.
  4. HE t-shirt.
  5. HE t-shirt.

I am the tester of all the problems. I'd like to thank the problem setters Sanjay Gidwani (sanjaygidwani), Mohd Salik (abx_2109), Orap Andrew (Dalgerok), Saurabh Joshi (Apptica) and Anand Jaisingh (.AJ.).

The contest will be RATED.

Happy Coding :)

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By isaf27, history, 23 months ago, translation, In English

Problems A-G have been created by isaf27. The idea of the problem A has been offered by i_love_isaf27.

The problem H has been created by _kun_.

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Jury's solution: 44522356

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Jury's solution: 44522430
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Jury's solution: 44522470
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Jury's solution: 44522488
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Jury's solution: 44522506
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Jury's solution: 44522527
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Jury's solution: 44522542

Solution by Endagorion: 44519413 (maximal spanning tree)

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Jury's solution: 44522571

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By isaf27, 23 months ago, translation, In English

Hi all!

I'm happy to welcome you at the Div.1 and Div.2 shared rated round Mail.Ru Cup 2018 Round 1, it will start at Oct/18/2018 19:35 (Moscow time). The problems were prepared by me — Ivan Safonov. I'd like to thank Dmitry _kun_ Sayutin for an idea and preparation of one of the problems and Egor I_love_isaf27 Gorbachev for an idea for another one.

This round is the first round if the new championship called Mail.Ru Cup, you can learn more about it following the link. The round will be rated for everybody!

The championship feature the following prizes:

  • First place — Apple MacBook Air
  • Second and third place — Apple iPad
  • Fourth, fifth, sixth places — Samsung Gear S3
  • Traditionally, the top 100 championship participants will get cool T-shirts!

In each round, top 100 participants get prize points according to the table. The championship's result of a participant is the sum of the two largest results he gets on the three rounds.

Huge thanks to Grigory gritukan Reznikov and Ilya izban Zban for testing the problems, to Nikolay KAN Kalinin and Ildar 300iq Gainullin for their help in preparation, and to Mike MikeMirzayanov Mirzayanov for Codeforces and Polygon platforms.

The round will feature eight problems to solve in two and a half hours. The scoring will be announced closer to the beginning of the round.

I hope everyone will find some problems interesting. I wish everybody a successful round and a positive rating change!

Good luck!

UPD1,Scoring distribution:

500 750 1250 1500 2000 2250 3000 4000

Congratulations to the winners of Round 1!

  1. mnbvmar
  2. Um_nik
  3. V--o_o--V
  4. LHiC
  5. lewin

UPD2

Editorial

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Announcement of Mail.Ru Cup 2018 Round 1
 
 
 
 
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By isaf27, history, 2 years ago, In English

Hello CodeForces Community! Once again we bring to you a fresh set of programming challenges with the June Lunchtime 2018, a three-hour contest of your coding abilities. Hope to see you all join us and challenge for the top spot!. Joining me this time on the problem setting panel are:

  • Problem Setter: isaf27 (Ivan Safonov)
  • Problem Tester: kingofnumbers (Hasan Jaddouh)
  • Editorialist: likecs (Bhuvnesh Jain)
  • Admin: kingofnumbers (Hasan Jaddouh)
  • Statement Verifier: xellos (Jakub Safin)
  • Russian Translator: CherryTree (Sergey Kulik
  • Mandarin Translator: huzecong (Hu Zecong)
  • Vietnamese Translator: (VNOI Team)

Contest Details:

Time: 30th June 2018 (1930 hrs) to 30th June 2018 (2230 hrs). (Indian Standard Time — +5:30 GMT) — Check your timezone
Contest link: https://www.codechef.com/LTIME61 Registration: You just need to have a CodeChef handle to participate. For all those, who are interested and do not have a CodeChef handle, are requested to register in order to participate. Prizes: Top 10 performers in Global and Indian category will get CodeChef laddus, with which the winners can claim cool CodeChef goodies. Know more here: https://discuss.codechef.com/questions/51999/how-do-i-win-a-codechef-goodie
(For those who have not yet got their previous winning, please send an email to winners@codechef.com) Good Luck!
Hope to see you participating!!
Happy Programming!!

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