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Codeforces celebrates 10 years! We are pleased to announce the crowdfunding-campaign. Congratulate us by the link https://codeforces.com/10years.
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Tutorial of Technocup 2019 - Elimination Round 4

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Thanks for fast editorial

so fast

I want to ask questions about the solution F:the 2

^{n}polynomials,is it should ben^{2}polynomials?2

^{n}since the inclusion-exclusion formula is used in the proof. But it is only the proof that the main function is a polynomial, we don't need to actually compute all these 2^{n}summands.Out of curiosity, may I ask problemsetters about their views to criticism on Div1C? There seems to be quite negative feedback to this problem. Do you think it is reasonable to appear in CF rounds? Do you think people's criticism make sense? Thanks.

I am not a setter of this problem, but I considered it to be OK when it was proposed. Perhaps it would be better if we didn't ask for a certificate.

But I still don't quite understand why it received such an amount of hate. There are problems which at first seem like handling a lot of corner cases without applying any specific idea, but if contestant thinks carefully before starting to write code, then he can reduce the length of this solution and the number of cases he needs to handle. I understand how this problem can be seen as a bad one if someone picks the first solution idea that comes to his mind and starts implementing it right away, but is it a good strategy on contests?

I didn't understand that in problem link 1085-B

how can we get this result : x= p*(n−p)/k ? Please Help.

can anyone please explain the following lines from "Minimum Diameter Tree" for dummies: "Note that the contribution to the sum on the right side of the inequality of the weight of each edge will be at least l−1, because any edge lies on ≥l−1 paths between the leaves of the tree. So, ∑1≤i<j≤ldistaiaj≥(l−1)⋅∑e∈Eweighte=(l−1)⋅s"

same here , didn't got it either. Hope someone explains.

I think there is mistake in B editorial. There is should be x = (nk + p^2) / p, not x = p * (n — p) / k.

can someone provide easier explanation for the problem div-2 D, or how they were able to get this approach