Please, try EDU on Codeforces! New educational section with videos, subtitles, texts, and problems. ×

Endagorion's blog

Technocup 2019 — Elimination Round 4 + Codeforces Round 528: editorial
By Endagorion, history, 18 months ago, translation, In English,
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial is loading...
Tutorial of Codealittle Contest-1
 
 
 
 
  • Vote: I like it
  • +26
  • Vote: I do not like it

Comments Comments (14)
»
18 months ago, # |
  Vote: I like it +120 Vote: I do not like it

Thanks for fast editorial

→ Reply
»
18 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I want to ask questions about the solution F:the 2 n polynomials,is it should be n 2 polynomials?

→ Reply
  • »
    »
    18 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    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.

    → Reply
»
18 months ago, # |
  Vote: I like it 0 Vote: I do not like it

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.

→ Reply
  • »
    »
    18 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    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?

    → Reply
»
18 months ago, # |
  Vote: I like it 0 Vote: I do not like it

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

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

→ Reply
»
18 months ago, # |
  Vote: I like it 0 Vote: I do not like it

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"

→ Reply
  • »
    »
    9 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

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

    → Reply
    • »
      »
      »
      2 months ago, # ^ |
        Vote: I like it +1 Vote: I do not like it

      I know this thread is quite old, but I'll write this for any future visitors

      Consider any edge $$$ \displaystyle e \in E $$$ and let $$$ \displaystyle x , y $$$ be the number of leaves on either side of the subtrees of this particular edge. Then the number of paths between leaf vertices, such that $$$ \displaystyle e $$$ belongs to this path is given by $$$ \displaystyle x*y. $$$ If $$$ \displaystyle l $$$ be the total number of leaves, then we have $$$ \displaystyle x + y = l. $$$ Therefore, the minimum number of paths (leaf to leaf) in which the edge $$$ \displaystyle e $$$ is a part of is, when there is one leaf on one side and $$$ \displaystyle l - 1 $$$ leaves on the other side. Hence each edge will be part of atleast $$$ \displaystyle 1*(l-1) = l- 1 $$$ paths.

      → Reply
»
18 months ago, # |
  Vote: I like it 0 Vote: I do not like it

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

→ Reply
»
18 months ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

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

→ Reply
»
5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

could not understand problem 1085-B

→ Reply