likecs's blog

Invitation to September Mega Cook Off on Codechef
By likecs, history, 7 years ago, In English

Hello Codeforces community,

Get ready for an exciting Sunday action your way.

This Sunday, 17th September, from 9:30pm to 12:00am (IST) Codechef is organising Mega Cook off for ICPC aspirants from around the world.

The panel for the contest consists of :

  • Problem Setter and Editorialist : likecs(Bhuvnesh Jain)
  • Problem Tester : kingofnumbers(Hasan Jaddouh)
  • Admin : kingofnumbers(Hasan Jaddouh)
  • Russian Translator : CherryTree(Sergey Kulik)
  • Mandarin Translator : huzecong(Hu Zecong)
  • Vietnamese Translator : Team VNOI
  • Language Verifier: (Priyank jaini)

I would also like to thank Codechef team and Praveen Dhinwa (PraveenDhinwa) for help in preparing the contest.

Hope you will enjoy solving the problems. The editorials with the model solutions will be available right aafter the contest. Please give your feedback on the problem set in the comments below after the contest.

Please find the rest of the details about the contest below.

Time: 17th September 2017 (2130 hrs) to 18th September 2017 (0000 hrs). (Indian Standard Time — +5:30 GMT) — Check your timezone.

Details: https://www.codechef.com/COOK86

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 school students each from Global and Indian category will get CodeChef laddus, with which the winners can claim cool CodeChef goodies. Know more here: https://www.codechef.com/laddu. (For those who have not yet got their previous winning, please send an email to winners@codechef.com).

In addition to the above prizes, top 50 Indian students will get their ACM-ICPC expenses reimbursed. For more details refer here.

The main characters of the contest are Chef Dobby and Bhuvan.

Good Luck! Hope to see you participating!!

UPD 1: The contest starts in 25 minutes. Best of luck.

UPD2: The contest has started.

UPD3: The contest has ended. Congratulations to all the winners and also everyone who solved the complete problemset.

The global top 5 (also overall top 5) are :

  1. tourist (Special Congratulations for completely solving the contest in just 34 minutes).

  2. uwi

  3. RAVEman

  4. zeliboba

  5. I_love_Tanya_Romanova

The top 5 Indians are :

  1. jtnydv25

  2. saharshluthra

  3. gvaibhav21

  4. architkarandikar

  5. abisheka

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

Is Bhuvan a coder or a cricketer?

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    7 years ago, # ^ |
      Vote: I like it -23 Vote: I do not like it

    Both, as both are competitive games ;)

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7 years ago, # |
  Vote: I like it +27 Vote: I do not like it

Should a guy with 1600 rating really be setting a whole contest ?

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

    See his rating on Codechef. Further, there are lots of people who do not perform very well in short time contests, but are great at maths and algorithms. Search him on wikipedia Darooha

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      7 years ago, # ^ |
        Vote: I like it +15 Vote: I do not like it

      Why is his rating low if he is great in maths and algorithms ? He has participated in 53 rated contests till now. Maybe he should prepare long contests instead of short ?

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

      Did you just compare him with the inventor of link-cut trees ? xD

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

        No i'm not comparing him with the inventor of link-cut trees. I'm just stating that having a low rating doesn't imply that someone can't be a good problem setter.

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    7 years ago, # ^ |
      Vote: I like it +19 Vote: I do not like it

    Should a guy with only 7 rated contests and a 1736 rating really be deciding who gets to set a whole contest?

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7 years ago, # |
  Vote: I like it -6 Vote: I do not like it

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

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

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

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

I liked the problems!

Feedback:

LIKECS02, I didn't proved my solution just printed an array centered at n, and stressed for all possible cases.

LIKECS03, I confused the problem and solved it for xor instead of or! the or case is trivial

LIKECS04, Nice one, again I didn't had time to prove it, just generated all possible numbers in the final array and then dp.

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

    Stressing for all possible cases sounds like a good proof :)

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    7 years ago, # ^ |
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    For LIKECS03 can you discuss your approach for the xor invariant.I too misread the question and then couldn't solve it.

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      7 years ago, # ^ |
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      Cant we find the basis in mod 2 field and then answer it

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7 years ago, # |
← Rev. 3   Vote: I like it +7 Vote: I do not like it

Codechef Discuss forum is down a moment. Till the you can find all the contest material : problem statements, editorials, model solutions in c++, java and python, bonus problems for every question etc are available at https://github.com/likecs/COOK86 .

Hope you all enjoyed the contest.

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7 years ago, # |
← Rev. 3   Vote: I like it 0 Vote: I do not like it

How to solve the fourth problem? I had assumed an unproven claim that the product of gcd of the numbers in the array a[] and some power of 2 should be the sum of numbers in a[]. It somehow worked for all the examples I could come up with during the contest :P

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    7 years ago, # ^ |
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    The proof will be available in editorial with worked out example. You can check the github link for it as codechef discuss is down for a moment.

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7 years ago, # |
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Since, Codechef Discuss is back again, you can find the detailed editorials here :

https://discuss.codechef.com/questions/111311/likecs01-editorial

https://discuss.codechef.com/questions/111318/likecs02-editorial

https://discuss.codechef.com/questions/111615/likecs03-editorial

https://discuss.codechef.com/questions/111543/likecs04-editorial

https://discuss.codechef.com/questions/111866/likecs05-editorial

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7 years ago, # |
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For the fourth problem, I made dp[winning/losing][index][ sum ] , I chose k between 0 to b[index]. I found a pattern that whenever sum=3*(2^something)*k it will be a losing position else it will be a winning position.Surprisingly O( 50^4 ) is giving TLE. Was my approach right?

code

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

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7 years ago, # |
  Vote: I like it +14 Vote: I do not like it

I must like contest where I solved one task before than all other participants :D

Nice tasks, for me contest was very interesting :)

I really want to know how many coders proved solution for the fourth task, I spent a lot of time to guess right condition and I didn't find it. Now a lot of contests have some constructive algorithms and some "guessing tasks" ( read AtCoder :P ) and I can not solve it in 90% of cases.

I know there is math behind it, but I think intuiton is more important here.

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