We invite you to participate in CodeChef’s September Cook-Off, this Sunday, 20th September, from 9:30 PM to 12:00 AM IST.

2.5 hours, 5 problems.

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.

Joining us on the problem setting panel are:

Setters: Manish Tanwar manishtanwar , Naman Jain smartnj

Tester: Rahul Dugar amnesiac_dusk

Statement Verifier: Jakub Xellos Safin

Editorialist: Ritesh rishup132 Gupta

Admin: Teja cache Vardhan Reddy

Mandarin Translator: Qingchuan UoA_ZQC Zhang

Vietnamese Translator: Team VNOI

Russian Translator: Fedor Fedosik Korobeinikov

Bengali Translator: Mohammad solaimanope Solaiman

Hindi Translator: Akash devils_code Srivastava

**Prizes:**

The top 10 Indian and top 10 Global participants will receive CodeChef laddus, with which the winners can claim cool CodeChef goodies. Know more here.

Good luck and have fun!

How to solve MININS(Minimum Insertions)?

How to solve Joined Subarrays on Tree? Can someone help me find what's wrong with my solution? I was struggling with it for 1.5h. https://www.codechef.com/viewsolution/38064446

I havent undrastand your solution but your code is so so so clean! Good job

I used the same approach bro and was stuck for around 1 hour

If anyone finds a testcase, do share :-)

It fails on test 33234, I dont know why I was convinced that it is correct ;p

The answer should be 4 ryt??

If yes, I guess my solution was different after-all -My approach

If anyone finds a testcase , do share becoz its killing me as I have tried loads of testcases...

can someone please give few tricky test cases of bulbs problem? Please

check the youtube videos made by codechef

or you can check my greedy solution, but i have not given an in depth explanation

The contest is over. Editorials are uploaded at Codechef Discuss. So, you can check them out.

The Editorial of GPHLBL is not there. Will it be posted later?

Oh. I think yes. short explanation: We can construct scc of input graph. we can reduce constraints such that we finally have some constraints that c1 type edges incoming or outgoing for a particular connected component or node are between l to r. Now, let us assume c1<c2 without loss of generality. Now, let us create a flow network where flow models the number of c1 type edges. Now, we can create a four layer graph where source to first layer represents the scc's outgoing demands, first to second layer represents node's outgoing demands. Second to third layer, represents the edges, third to fourth layer represents node's incoming demands and fourth to sink represents scc's incoming demands. These can be done with flow with lower bounds which is standard problem.

Besides, The editorial will be uploaded soon. I wrote this on phone so sorry for mistakes or unclearness. Code for reference: https://ideone.com/GDb7oa

Thank you! I think you can just post your explanation as editorial because it's clear enough.

Please provide better samples and also include explanations next time. I see no harm in doing it.

A good sample or sample explanation helps us resolve any misunderstanding of the problem. I spent a good 45 mins thinking, coding and testing a problem I misunderstood

In

Maximise Subsequence Value,I have done the silly mistake ,I was printing the position of elements in 0 based indexing ,as a result I got 3 WA. submission link . Codechef should add the feature to show the verdict on samples test cases(Accepted or Wrong answer)I disliked weak samples and the lack of explanations for them -_-

Interesting fact: while everything else was quite easy, it took me half an hour to come up with a solution for the easiest problem, MVAL https://www.codechef.com/COOK122A/problems/MVAL

my screencast: https://youtu.be/RCwIm5toNhc

The code which I wrote (for Balancing Game) is working for all the testcases I think of. It would be very helpful if someone could provide some counterexample.

Link to my submission Balance Game

I used the concept of subset sum to approach the problem and shifted all the number to positive by adding the min element to all the numbers.

Please help.

I got the problem. I misunderstood the reordering part.

Did any top performer receive the free subscription offer for unacademy yet? I actually had unsubscribed from their mail as it was quite annoying and now I feel they would have send the message regarding the free subscription in the mail.

Yes, got the email reach out to them and mention it

Also you had to apply before the contest to be eligible for the contest

Weak test cases in Bulbs

Many of the have passed for : 11 2 00010000100 The answer is 4 but a lot of submission giving answer 5 have been passed.

manishtanwar do you agree with us?

Can someone please explain the question of minimum insertion? I am not understanding what the question means.

The explanation of the problems was not so clear!

codechef needs to provide some more test cases so that when we build our solution , we could be sure that we have interpreted the problem in the way they said. because If we know the solution and get penalities free of cost due to misinterpretation is too bad. One of the reason I don't like cookoff. The minimum insertion was too confusing and required mathematical reasoning to understand the problem. If they would have given sufficient test case we can be assured that what we are doing is right or wrong.

Weak samples

Problems were toooo hard!!

I was able to solve 0 problems in this contest!

Haha

Is it just me who found the problem statement for MININS... extremely poor

too many nots and the irrelevant use of the word subsequence...

Yes, I also found the statement very confusing. Assuming I now understand it correctly, I guess they could have just written:

For each $$$K$$$ from $$$2$$$ to $$$N$$$ inclusive, find the smallest possible number of elements that need to be inserted into $$$A$$$ to form a sequence $$$B$$$, such that all continuous subarrays (in a circular sense) of $$$B$$$ of size $$$K$$$, have at least one pair of consecutive elements which are co-prime.

That would be much clearer, I suppose. (Ignoring the fact that I still couldn't solve it).

Here, is the official video editorial for MVAL [I have tried to keep the solution short and simple]. The question was quite easy but got surprisingly less number of submissions in Div B. I think most of the users either misread the question or didn't read the question at all! Let me know if you found the video editorial useful :)

List of wrong solutions of BULBS which got accepted during the contest

https://www.codechef.com/viewsolution/38075458

https://www.codechef.com/viewsolution/38070932

https://www.codechef.com/viewsolution/38068775

https://www.codechef.com/viewsolution/38071771

https://www.codechef.com/viewsolution/38063231

https://www.codechef.com/viewsolution/38053841

https://www.codechef.com/viewsolution/38071897

https://www.codechef.com/viewsolution/38069473

https://www.codechef.com/viewsolution/38077809

https://www.codechef.com/viewsolution/38067122

https://www.codechef.com/viewsolution/38070571 (Swag wala function)

https://www.codechef.com/viewsolution/38062954

https://www.codechef.com/viewsolution/38067990

I have checked only the first 4 pages of 48 pages of accepted submissions and found this much. The last time when the wrong solutions got accepted during a rated contest, that contest was turned into an unrated contest( https://www.codechef.com/DEM2020?itm_campaign=contest_listing ). Will codechef make this cookoff unrated too or it will continue showing soft corner for two offical short contests?