yes, I have seen a submission following this idea somewhere

FireFly __baozii__

Please correct me if I am wrong for problem div1C.

In editorial, for the third summation, there should not be x<y condition when d(x)=d(y) as tom would win for both cases when x<y || x>y. maybe a multiplication factor of 2 should be there outside the third term.

Edit:Nvm, got it.First two term includes that contribution already which is also clear by the way you are calculating the first two terms.Really good Problemset.

360866947

This is my submission for problem B which one can refer as it is kind of mix of dp and greedy as I try all possible ways when I am not sure of which bits need to be placed for some bit i.

If you have any doubts, Feel free to ask. I will try to clarify.

I thought(and wrote) of a solution for problem G using diameters but it uses ceil(n/2) +1 queries.

Was it intentional to not let pass that solution KluydQ ?

Did nobody else think this for problem H(Remove The Grail tree).

First observation was to build a Forest of all ones same as editorial.Then focussing on a particular tree, Let's imagine a node(u) which has even number of neighbours(all 1s) and is also at the greatest depth in this current tree. Then for sure we can say that deleting this node first is always optimal.

Why?

Proof:Let's say we deleted it's parent before u(say p). then u will now have odd neighbours(all 1's) and now there is no way possible to make the neighbours of node u even again as by definition node u is the deepest node with odd neighbours and hence no one left down there to delete.

Now, just keep on repeatig this process, removing the node with deepest odd neighbours and after deletion all neighbours which were good now becomes bad and which were bad now becomes good. all the neighbouring 0's shall be immediately removed after this process as well and we are done with the solution. You can refer my submission for implementation details. 360032537

P.S.-> I really really liked the editorial's idea but I find this idea very straightforward to think.

Can someone try hacking my code as well please.I believe it should work fine as constraints are 2e5.(why using walk un-necessarily) It is n((logn)^2) only. Here is my 357542232.

Problem F and G felt too standard.(I am not really complaining) But I think particulary G should involve something more tricky(even if educational) than just using one simple observation and bam segment tree.....AC. overall I enjoyed solving problem E the most.Used segment tree for E as well as I couldn't come up with the merging thing.

imo, problem E could have been really hard if a guess was not possible from the max number of queries allowed and typical sum setup which demands for B.S. in interactive problems.

here is my solution for D which can easily be extended to Bonus of D as well. 355263118 Feel Free to ask if any further clarification needed. (I modelled as decreasing subsequence dp)

Thanks for sharing!

Which problems did everyone found most interesting/toughest/tricky? Please share problemset link if available.

very well spoken.(upvoted) It's a big concern for me as well as a participant as creating new problems with fresh ideas has become really difficult for authors especially after AI has gotten so strong. Further discouraging the authors and co-ordinators for petty reasons(just because they got negative delta) would further decrease the frequency of the rounds on CF. Will make sure to appreciate the rounds I participate in future.

same. could you please comment under this blog if you get to know about any further updates?

Great work!!

It's actually gonna motivate me to solve more harder problems as i can actually see my heat map changing color based on my practice.

Cool!! Back to Back dominator rounds.

Excited and hoping to get some positive delta in my first ever div.1 contest. good luck everyone!!

ohkay nice then.

It's clashing with CF Round man.

can't you postpone it?

Thanks man! got it

Am I the only who is getting TLE in H after using segment trees effeciently(as far as i know) Can someone help me to optimize it ? 305573607

what's the basis to select a team that's getting selected from both chennai regionals and amrita regionals to select it from chennai regionals only. most of the teams from chennai are also getting selected from amrita but they have just taken complete seat for those teams from chennai. last time for such cases, 0.5 seat was taken from both sites.

Just look at the huge dip of rank selection from chennai regionals compared to last time. (last time it was 19 but this time 10)

Can we mail someone to address this issue?

I am unable to find the wrong case for my submission on G it's WA on 4. Can someone give some test case for it.

here is my submission:303466389

How are people solving problem E with small to large merging?

I want to get more familiar with that concept but I am not able to come up with the solution from that approach

Thanks for the explanation. I will try builiding the solution on it

can someone provide some hint for problem D or from where did you start building your solution

I am stuck at how to view the operation even if i fis all the values at all the nodes.

I actually used DP on trees and i don't know why but my solution is failing on Test case 2 C ripped my whole contest. missed D by 5 minutes.

here is my submission if someone would like to help 302414968

P.S.-I personally liked the contest problems

For problem F, the solution 1 that is described in the editorial for computing non-unity sequences for length till 16 using dp. You can actually do it using inclusion and exclusion too.

Could you please elaborate on how the camp would plan the schedule for online participants. Like will there be post contest discussions in recorded or live format. And same follow-up question for algorithmic techniques teaching.

I think that is mainly due to two reasons:

1.most of the people are busy preparing for the internship or busy working in summer internships.

2.People get more fired up one or two month before the regional and subregional contests and hence more participation in winter

When will the official final rank list gonna be released ?

Good to see a DandaDan fan here yo....

itna sach bhi nahi bolna tha bhai.

Team:'Fast Funk Transform' from IIT Dhanbad

Members:moradiya84 Vaid23 devansh789

Regionals: Qualified for Chennai.

Story behind teamName: We wanted to name our team after some hardcore algorithm(that we actually know lol) and wanted the name to be 'Fast Fcuk Transform' but we changed it in fear that might get banned due to NFW stuff.

Preferences in Problemset: obviously,FFT:). Hope to connect with folks coming to chennai

I think you did not understand my comment. Look at the code, it's wrong.

The Question Random nim is not tested properly. You can see and view that this submission is clearly different from the author's code and it's still getting accecpted because there is no test case present where the xor of the array is getting zero. There are many such submissions with completely different approach getting accecpted due to this. https://www.codechef.com/viewsolution/1104769988 It should be retested and re-evaluated

I did not understand problem 6 -> Small powers of subtree. We made a dp[v][i]-> number of ways to choose an ordered sequence of length i from this subtree. But while doing transition dp[u][i]+=dp[v][i];dp[u][i+1]+=dp[v][i]*some constant.......dp[u][k]+=dp[v][i]*some constant. I did not understand the transitions as the length of sequence i made from some nodes of subtree of v might not include the node v itself and hence directly including node u into the sequence made from subtree of v might not necessarily make a connected subgraph So are we defining our dp[u][i] like ->number of ways to choose an ordered sequence of length i from this subtree while one of the points being node u ?? please clarify.

Thanks a lot. Got the flaw in my approach

Can someone Please tell why this Solution of E is giving WA. I have thought it for hours but unable to figure it out. https://atcoder.jp/contests/abc364/submissions/56048006

Thank you for replying.

I didn't understand the extension on the linear sieve part: basically, The relation between f(ip) and f(i),f(p). Can someone please elaborate on that

First Contest in cc div.1

Hope to remain 5 star after the contest.

Thanks a lot bro!

Oh! Sorry for not being clear. I read the editorial of the problem mentioned by 18o3 in the comment, not the contest's editorial.

My doubt lies in your last line, that how do we find maximum xor subset over the array. I saw the atcoder editorial and it was using some canonical row transformation which I was unable to understand that why was it working

I understood about XOR basis from this blog. **https://codeforces.me/blog/entry/100066** But how is this helping in finding maximum xor subset from a set? Thanks.

I read the editorial but I am unable to follow the row canonical optimization part and if possible could you also give some resource for the proof of why and how is it working.

Thanks!

Could Someone please give the idea or approach of problem C ? I tried thinking in direction of DP but got nowhere as range was too large to make submask as DP state. I tried some random constructive ideas but they didn't worked either. help appreciated.

Literally one of the best posts out there. It makes me want to learn more and more. thanks a lot.

Excited for this kind of contest. Also Hoping to become 5 star in this round. :)

yeah I figured and was trying to write up the code

Yeahhh, I got you.

Thanks bro.

Can someone please explain how to build segment tree in F??

I have thought till the part of sorting the tuples and all but being a beginner at segment tree, I am unable to understand the editorial

Hurray...!!!A contest made by alumni of my college.... looking forward to a great round and hope to reach 5 star.

Which college are you from??

could someone please explain the O(n.route(n)) optimised solution.I have understood the logic and the O(n^2) solution has been implemented but it would be grtt if someone could help me understand the optimisation implementation

https://codeforces.me/problemset/status?my=on why this code not working,I am unable to figure out after many WA attempts for Div.1 B

but now my code is giving TLE on test case 25. https://codeforces.me/contest/1746/submission/202518774 I don't think collisions occur in maps and when I saw other people's code,so they have used different method to store the answer than mine. can u give me some idea to optimise this approach or rough time complexity of this code

Can anyone explain me what's the space complexity of this code,I am getting MLE on test case 2. here's my submission: https://codeforces.me/contest/1746/submission/202337720

thanks a lot sir...!!!

can someone tell me the mistake in my code of problem G. I have done pretty much the same as editorial's approach,but I am getting WA on test case 14. (basically,my code is also including 0 in one of the outputs which I am unable to think of why) https://codeforces.me/contest/1759/submission/202043617

can someone please help me in question D.

i want to solve it without DFS and BFS as i dont know it yet.

can we solve it constructively??