### tourist's blog

By tourist, 14 months ago,

XX Open Cup Grand Prix of Gomel takes place on Sunday, February 16, 2020, at 11:00 AM Petrozavodsk time.

You need an Open Cup login to participate.

I'm the writer of all the problems. Let's discuss them here after the contest!

UPD: Thanks for your participation! Editorial is available.

• +135

 » 14 months ago, # | ← Rev. 3 →   +26 When I login into the page I get the following message: "The virtual contest is in progress. You are not allowed to participate".EDIT: Now both links given for Div 1. seem broken to me.EDIT2: fixed, thanks :D
 » 14 months ago, # |   +16 How to solve B and H?
 » 14 months ago, # |   +16 How to solve E?
•  » » 14 months ago, # ^ |   +10 Let $P(X) = \sum p_i \cdot x^i$. We need to find several first coefficients of $Q(x) = P(x) ^n$. We can write equation $Q'(x) = (P(X) ^ n)' = n \cdot (P(x) ^ {n-1})P'(x) = n \cdot Q(x) / P(x) *P'(x)$ So $P(x) \cdot Q'(x) = n \cdot Q(x) \cdot P'(x)$. If we write everything about $x^m$ it will give us a way to represent (m+1)-th of coefficient of Q(x) from deg(P) previous.
 » 14 months ago, # |   +26 Only after reading editorial for A I noticed that it's guaranteed that n is divisible by k. :)
 » 14 months ago, # |   +55 How can I obtain an opencup account? I've messaged snarknews on CF but got no response.
 » 14 months ago, # |   +28 There is linear solution for F based on fact we can calculate $f(k) = \sum\limits_{t\geq n} bin(k, t)$ for all k in linear time
 » 14 months ago, # |   +10 Instead of matching algorithms for G we can use much much simpler approach (especially when compared to blossom): take arbitrary unmatched vertex and match it to its random neighbour — if it that random neighbour was already matched before then unmatch it
•  » » 14 months ago, # ^ | ← Rev. 2 →   0 What about the bipartite part? This method works for it too?
•  » » » 14 months ago, # ^ |   +10 Yeah, works like a charm for both bipartite and non-bipartite case :)
 » 14 months ago, # |   +31 We can use the symmetric chain decomposition of the boolean lattice to solve the bipartite case for G constructively. You can read pages 5 and 6 of this slide.
•  » » 14 months ago, # ^ |   0 orz Retired_MiFaFaOvO teacher
•  » » 14 months ago, # ^ |   +1 Comments like this make me realize that I haven't even started CP xD
 » 14 months ago, # | ← Rev. 4 →   -20 Thank you , tourist. You are the best! tourist orz
 » 14 months ago, # |   +10 Will the mirror of this contest available anytime soon on Codeforces gym?