Dominater069's blog

Invitation to CodeChef Starters 167(Rated upto 5 stars) — 1st January
By Dominater069, history, 16 months ago, In English

We invite you to participate in CodeChef’s Starters 167, this Wednesday, 1st January, rated upto 5 stars (i.e. for users with rating < 2200).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

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Comments Comments (37)
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16 months ago, hide # |
← Rev. 2  
Vote: I like it +33 Vote: I do not like it

dom I am sorry i blamed you for Math puzzles. Its far better last weeks contest that my 10th grade brother could AK using gpt.

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16 months ago, hide # |
 
Vote: I like it +33 Vote: I do not like it

please atleast make div2 and div1 gpt proof. Last weeks contest was absolute dog shit.

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16 months ago, hide # |
 
Vote: I like it +30 Vote: I do not like it

I wish every honest participant a good first contest of 2025!

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

Nice

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

How much time does rating update take?

Also I'm doing a contest on codechef after a long time. It doesn't seem to have any of the "cookoff" or other contests. Just "STARTERS". What happened?

When I see the ranking, it's all 1-star profiles. Since it's rated upto 5-stars, atleast some top rankers should be 5-star rated? Does no one do codechef anymore?

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16 months ago, hide # |
 
Vote: I like it +4 Vote: I do not like it

Great Questions. Dom is back. Return of the king.

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16 months ago, hide # |
 
Vote: I like it +4 Vote: I do not like it

great problems !!! btw when is the editorial for icpc amritapuri regional round publish ?

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Why was Grid Construction Even placed below Grid Construction Odd in the order? Ig it made difficult to solvers, just because it was below.

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

too many problems of same difficulty in $$$div2$$$

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16 months ago, hide # |
 
Vote: I like it +11 Vote: I do not like it

Disclaimer:

Spoiler
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    16 months ago, hide # ^ |
     
    Vote: I like it +11 Vote: I do not like it

    Is it only me or was the problem wasn't as easy as the number of submissions made it look like?

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      16 months ago, hide # ^ |
       
      Vote: I like it +2 Vote: I do not like it

      It shouldn't have been (I guess it was solved by o1)

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        16 months ago, hide # ^ |
         
        Vote: I like it 0 Vote: I do not like it

        Is there any way you think we could stop this kind of submissions by gpt, as they are anyways not allowed according to site guidelines?

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          16 months ago, hide # ^ |
           
          Vote: I like it 0 Vote: I do not like it

          Not easily in terms of administration. Currently the only way to find out if a user is cheating with an LLM is checking their code style, but they can just rewrite easily. The preferrable option right now is to just make tasks that can't be solved by o1 (but this is hard)

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    16 months ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it 0 Vote: I do not like it

    I don't know about MCMF or used o1, but the solution was fairly simple to think about. Just a few lines of code:

    long long a, ans=0, val=0;
for(int i = 0; i < n; i++) {
    cin >> a;
    val += a;
    ans += abs(val);
}
cout << ans << endl;

    But yes I didn't expect it to have more solves than GRIDEVEN.

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    16 months ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it 0 Vote: I do not like it

    what was your mcmf based proof can you share ? i also think the construction is not at all trivial. nice proof thanks below

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      16 months ago, hide # ^ |
       
      Vote: I like it 0 Vote: I do not like it

      Consider the graph with $$$n+2$$$ vertices (including source and sink), which is almost a line graph with every edge having $$$1$$$ cost and $$$\infty$$$ capacity. The containers with positive temperature connects to the source, while the ones with negative temperature connects to the sink. The problem is equivalent to MCMF on this graph, except for some extra conditions.

      We will prove that the extra condition does NOT change the optimal cost. For this, consider a condition for an MCMF instance to have optimal costs. An MCMF instance must not yield negative cycles to be optimal. In our problem, we can see that we must NOT flow heat on one wall through both directions to not yield any negative cycles. And conversely, if each wall pushes heat through only one direction, the cost will be optimal.

      And there are constructions that achieve this. Consider a stack-based algorithm; you maintain two stacks $$$pos$$$ and $$$neg$$$ of tuples of $$$(index,flow)$$$. Whenever you find a vertex with nonzero demand/supply you push it to the corresponding stack. When $$$pos$$$ and $$$neg$$$ are both not empty, empty one of them by repeatedly sending flow from top of $$$pos$$$ to top of $$$neg$$$. Convenient invariants of this algorithm assure that at every moment, either every vertex in $$$pos$$$ leads $$$neg$$$, or every vertex in $$$neg$$$ leads $$$pos$$$. This, in turn, yields no wall pushing heat through both directions, meaning no negative cycles.

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16 months ago, hide # |
 
Vote: I like it -10 Vote: I do not like it

Why does every problem has to be based on a random observation ..CC Contest dissapoints everytime

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

I request Codechef to please at least provide a editorials of the contest for free.

If not then provide it for atleast 1 week for free.

I don't Know why they ask money for everyhting.

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

For the problem Grid Construction (Even) how is this output wrong? 

Input:
1
8

My Output:
1 2 3 4 5 6 7 8
2 1 4 5 6 7 8 3
5 4 1 6 7 8 3 2
4 7 6 1 8 3 2 5
7 6 3 8 1 2 5 4
6 3 8 5 2 1 4 7
3 8 5 2 7 4 1 6
8 5 2 7 4 3 6 1

S1+S2=(8×8)+(1×8)=72. The sum of any two adjacent rows or columns adds up to 72 as well

Are the solutions incorrectly checked?

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15 months ago, hide # |
← Rev. 2  
Vote: I like it +3 Vote: I do not like it

The problems were really nice

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15 months ago, hide # |
 
Vote: I like it +4 Vote: I do not like it

just a small request on codechef website, whenever I try to check out solutions to codechef problems, It notifies me saying to Get Pro to access text solutions of all the problems on CodeChef

but when I search for the problem tag in google, say I google searched: <tagname> codechef editorial, I could easily get to the discussion platform of codechef and view the editorials.

Can we just have the editorial displayed under the solution tab of each problem, because everytime whenever i needed to refer to codechef problem editorials, i used to search for the discussion page.

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