Ashishgup's blog

CodeChef September CookOff 2021 (with prizes and new admins!)
By Ashishgup, 3 years ago, In English

We invite you to participate in CodeChef’s September Cookoff, today — 19th September from 9:30 PM — 12:30AM IST.

The contest will be 3 hours long. There will be 7 problems in Div 1/2 and 8 problems in Div 3. It will be rated for all three Divisions.

Joining us on the problem setting panel are:

Problem Submission: If you have original problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Prizes:

Global Rank List:

  • Top 10 global Division One users will get $100 each.
  • Non-Indians will receive the prize via money transfer to their account.
  • Indian users will receive Amazon vouchers for the amount converted in INR.

Indian Rank List:

  • Top ten Indian Division One coders will get Amazon Vouchers worth Rs. 3750 each.
  • The rest in the top 100 will get Amazon Vouchers worth Rs. 1500 each.
  • First-time winners in Div 2 who make it to the top 200 for the first time will get Amazon Vouchers worth Rs. 750 each.
  • First-time winners in Div 3 players who make it to the top 200 for the first time will get Amazon Vouchers worth Rs. 750 each.

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Good luck and have fun!

Admin Note:

I would like to welcome Anton antontrygubO_o Trygub and Yahor 244mhq Dubovik who have recently joined CodeChef and will be admins of CookOff and Lunchtime as well.

The winners of July CookOff to August Lunchtime have been finalized and will receive an email in the coming week.

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Comments Comments (21)
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3 years ago, # |
  Vote: I like it -28 Vote: I do not like it

First Comment! xD

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3 years ago, # |
  Vote: I like it +83 Vote: I do not like it

Will Anton still coordinate Codeforces Rounds?

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

When will you distribute prize of August cook-off?

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

    Ask when July Cook-off prizes will get distributed! xD

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

    I just got a mail an hour ago confirming the prizes for the July and August Cookoff. (I suppose July Lunchtime was also processed but I didn't give that contest)

    The actual vouchers (for Indian top participants) haven't been sent yet though.

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      3 years ago, # ^ |
        Vote: I like it +1 Vote: I do not like it

      Yes I also got confirming mail about prizes for July Lunchtime

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

Am I the only one who hates the timing of CodeChef Cookoff?

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

Are there any prizes for non-indian div 3 participants?

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

How to solve Permutation and GCD set?

I got that if $$$m > log(n)$$$ or $$$s_{1} > 1$$$ the answer is 0 since its only possible if $$$s_{(i - 1)}$$$ divides $$$s_i$$$ for all $$$i > 1$$$ and the $$$gcd(a_1, \ldots, a_n) = 1$$$.

After that I got the $$$O(n logn)$$$ expected value dp idea (placed $$$i$$$ digits and at gcd $$$s_j$$$, prob of moving to $$$(i + 1, s_j)$$$ is $$$((n / s_j) - i) / (n - i)$$$, similar for $$$s_{j - 1}$$$)

But I have no clue how to solve this any faster.

Also really liked Pairdist and Half Sequence. Chess Kings felt a bit too standard for its position.

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

Oof, I missed the contest. How come Codechef CookOff happened on the 19th? Doesn't it usually happen in the last weekend before the next month?

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

As a participant, I loved the small and clear statements this time. Specially loved the problem Half Sequence

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3 years ago, # |
  Vote: I like it +13 Vote: I do not like it

How to solve CKCGAME?

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3 years ago, # |
  Vote: I like it +136 Vote: I do not like it

Here is some feedback:

  • FAKESWAP: Almost trivial. Ok.
  • PAIRDIST: This was very hard (considering its position in the problemset) for me. I spent a lot of time on the construction for $$$n=4$$$ (which, in the end, is very elegant). The statement is a bit artificial, the solution is nice. Nice problem.
  • HFSEQ: Standard problem. Easy to convince oneself that if $$$n$$$ is big the answer is yes (apart from special cases) and otherwise one can check all possible subsets. Asking for $$$gcd = 2$$$ instead of $$$1$$$ does not make any sense.
  • CKCGAME: Amazing problem. The question is just so natural, and the solution is clean and not obvious.
  • PGCDS: Simple and interesting statement, but the solution is a bit standard. This one felt easy for its position, for me it was just unrolling the statement until I had a full solution, no moment of "aha!". Nice problem.
  • ONEPILE: I thought about this one for 30 minutes, without understanding which positions are winning. The described game is very simple and therefore the problem is very good. On a side note, I don't like problems which are clearly split in two (here one has to find a characterization of winning positions and then count them) unless there is a clear reason (is there a reason in this case?).
  • STQ: I thought about this one for 30 minutes, coming up with a solution which gets TLE but I think is not too far from getting AC (that is, with some small changes it may become AC). For each query, choose randomly $$$30$$$ elements in the intervals, and for each prime which divides at least one such element find whether it divides the strict majority of the element in the intervals.

Overall, it was a very good contest. Thank you to the authors!

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

Problem .Half Sequence, please explain anyone .

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

I never cared about cheaters. I always knew that these ratings are just numbers that have no value in the outside world, but today during the contest, when my rank was around 15-20 (in div 3) for more than 2 hours, and suddenly it dropped to 300, I realized that it is not just a rating that gets affected, but the whole motive of "competition" goes into vain.

These are just my personal opinions. I am not going to write some blogs or anything for these cheaters but just wanted to tell these cheaters don't even understand the meaning of "competitive programming."

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

    Is it normal for people like you to have rank around 15-20 in div3? This was just my first codechef contest and I finished at rank 302 there. Started slow, but gradually went up in ranks. And I messed up the FAKESWAP problem, so I can't say that I was particularly happy about my performance.

    I registered at codechef only thanks to this announcement on CF. Because I have high expectations of their new admins. And I think that some of the top positions in the div3 scoreboard may be occupied by new registrants IF there was any significant influx of new users. Or maybe you are right and just a spike of cheating explains it all.

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3 years ago, # |
  Vote: I like it +11 Vote: I do not like it

Any directions on what we need to do to get the coupon code , I have got the mail today , but don't know when and where to find coupon code

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3 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

are the prizes for August LunchTime rolled out? or even any confirmation mail

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