erniepsycholone's blog

Codeforces Round 929 (Div. 3)
By erniepsycholone, 10 months ago, In English

“It is not important to be better than someone else, but to be better than you were yesterday.” — Master Oogway, Kung Fu Panda

Hello, Codeforces! We are proud to present Codeforces Round 929 (Div. 3), and we hereby invite all of you to take part in it. This round will start on Feb/27/2024 17:35 (Moscow time). You will have 2 hours and 15 minutes to solve 7 problems. The penalty for a wrong submission is equal to 10 minutes.

This round will be rated for participants with ratings lower than 1600. However, all of you who wish to take part and have a rating of 1600 or higher, are welcome to register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks.

Remember that only the trusted participants of the third division will be included in the official standings table. As stated in this blog, this is a compulsory measure for combating unsporting behaviour and upholding gracious professionalism. To qualify as a trusted participant of the third division, you must:

  • take part in at least five rated rounds (and solve at least one problem in each of them)

  • do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

The problems were authored and prepared by erniepsycholone, snowysecret, dbsbs, jerryliuhkg, lomienyeet, and our beloved coordinator Vladosiya.

We would like to thank:

We hope that this contest, regardless of your background, rating and result, will increase your exposure to competitive programming and make you better than you were yesterday. Have fun!

UPD: Let's continue the streak of announcements with photos of the authors. This time with our coordinator and testers :)

UPD2: We discovered the screencast from Um_nik a short while before the end of the contest, and it had around 400 views by the end of the contest. Round is still rated, however, people who have used his solutions will be punished.

UPD3: Editorial is out

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10 months ago, # |
  Vote: I like it +49 Vote: I do not like it

As a part of the problemsetting team, we unfortunately cannot offer any competitive programming socks as prizes.

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10 months ago, # |
  Vote: I like it +43 Vote: I do not like it

{Get's a -200 Δ} "There are no accidents" $$$-$$$ Master Oogway, Kung Fu Panda

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10 months ago, # |
  Vote: I like it +11 Vote: I do not like it

As a coauthor, I encourage everyone to participate, regardless of your ratings. I also hope you enjoy the problems. :)

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10 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Wish to become an expert with this round :)

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10 months ago, # |
  Vote: I like it +24 Vote: I do not like it

As a grandmaster testing...

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    10 months ago, # ^ |
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    As an international master, I am disappointed that there has been no international master testing.

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10 months ago, # |
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Time to unleash the inner Kung Fu Coder and make Master Oogway proud! #CodefuPanda

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10 months ago, # |
  Vote: I like it -6 Vote: I do not like it

Will become Expert after this contest

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10 months ago, # |
  Vote: I like it +37 Vote: I do not like it

As a tester, I cannot pupil

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10 months ago, # |
← Rev. 2   Vote: I like it +6 Vote: I do not like it

As one of the testers of this round (i definitely dropped to specialist on purpose to get my own line in the round announcement), I unfortunately did not receive any competitive programming socks for my testing efforts.

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10 months ago, # |
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After rating rollback i became Expert so this is my first Unrated Div3 :)

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10 months ago, # |
  Vote: I like it +129 Vote: I do not like it

Random meme:

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10 months ago, # |
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maybe you can translate the saying into master turtle.

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10 months ago, # |
  Vote: I like it -13 Vote: I do not like it

As a participant, CR7 is GOAT.

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10 months ago, # |
  Vote: I like it +3 Vote: I do not like it

nice ạ

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10 months ago, # |
← Rev. 2   Vote: I like it +6 Vote: I do not like it

As a tester, I encourage every fellow programmer participating in the round to look at every problem to prevent skill issue. But anyways I hope everyone participating can have fun and hopefully learn something from this well crafted round~~

(The problemsetting team has genuinely dedicating a whole load of time to make sure this round runs smoothly with great problems!)

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10 months ago, # |
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NEW DIV 3 ROUND YEAHHH

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10 months ago, # |
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so many dbs students no kgv fame :( (dbs op)

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10 months ago, # |
← Rev. 2   Vote: I like it +6 Vote: I do not like it

Master Oogway quote beautifully encapsulates the essence of personal growth and self-improvement. Focusing on our own progress rather than comparing ourselves to others is a valuable mindset to adopt. Each day presents an opportunity for us to strive for excellence and become the best version of ourselves. Thank you for sharing such a meaningful perspective!

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10 months ago, # |
← Rev. 2   Vote: I like it +10 Vote: I do not like it

As a tester, I wish you high rating and hope you achieve the rank you aspire to be :)

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10 months ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

The secret ingredient is... !

Spoiler
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    10 months ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    Actually, the secret ingredient is... !

    Spoiler

    Big respect to Master Oogway though.

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10 months ago, # |
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It's time to make yourself and you better♥♥♥.

"Goodluck.", — Master Oogway, Kung Fu Panda.

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10 months ago, # |
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ok

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10 months ago, # |
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I hope I get blue :)

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10 months ago, # |
  Vote: I like it +7 Vote: I do not like it

the quote hits really hard...

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10 months ago, # |
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i wish i could solve A,B,C.

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10 months ago, # |
  Vote: I like it -16 Vote: I do not like it

DBS forces

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10 months ago, # |
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Finally unrated for me!

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10 months ago, # |
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GOOD LUCK !!!

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10 months ago, # |
  Vote: I like it +15 Vote: I do not like it

Cumulative sum of their age is less than me or they looks very young?

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10 months ago, # |
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Nice, new round, new training. BOTAAAAAAAT

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

Finally, another round where I can try hit pupil!

Good Luck for everyone!

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

Ohhhh,I see Atletico Madrid fan

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

I hope to solve AE

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10 months ago, # |
  Vote: I like it +18 Vote: I do not like it

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10 months ago, # |
  Vote: I like it +45 Vote: I do not like it

Kids are writing problems for a grownup like me. I guess that is the benefit of receiving a good education right from your childhood. The first time I used a computer was when I entered college :(

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10 months ago, # |
  Vote: I like it +7 Vote: I do not like it

I predict that there would be a problem involving some range queries or stuff like that probably C or D It would have a simpler solution but will be overkilled by many using segment trees or something similar.

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

I hope to successfully enter the youth league tonight ：）

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

Hoping for a fun contest.

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

give me a chance that making my name become yellow!

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10 months ago, # |
  Vote: I like it +21 Vote: I do not like it

Thanks for continuing streak of putting authors pictures on the contest blog

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

Good luck to everyone!

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10 months ago, # |
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Hope fast ABCD

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10 months ago, # |
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Mathforces

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10 months ago, # |
  Vote: I like it +10 Vote: I do not like it

LOL, umnik_team uploaded the solutions before the end of the div

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +20 Vote: I do not like it

    Why did you write this here!? Now there will be a lot of cheaters!

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10 months ago, # |
  Vote: I like it 0 Vote: I do not like it

um_nik is 1 hour ahead of us(iykyk)

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10 months ago, # |
  Vote: I like it +28 Vote: I do not like it

WTF is this? why were the solutions posted before the round ends by Um_nik??? This is not fair. I hope they dont make this round unrated because of this.

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    10 months ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    The problem-setting team has acknowledged the issue, and I have already tried my best to contact Um_nik on the issue a while ago to try to remove the video. I also hope the round doesn't get unrated :(

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      10 months ago, # ^ |
        Vote: I like it +2 Vote: I do not like it

      What is the use of removing now? The damage is already done

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        10 months ago, # ^ |
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        the video was there for more than 30 mins too, why didn't here remove it earlier

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        10 months ago, # ^ |
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        We contacted him before the round ended of course.

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    10 months ago, # ^ |
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    Most of the participants wouldn't have even seen the video. Hope contest doesn't get unrated (even though I couldn't implement E), as I truly enjoyed the contest.

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10 months ago, # |
← Rev. 2   Vote: I like it +1 Vote: I do not like it

..

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10 months ago, # |
  Vote: I like it +73 Vote: I do not like it

Thanks for the fast editorial!

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10 months ago, # |
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I hate myself for not reading problem E correctly I was able to do it in 10 min once, I read the statement properly...

anybody did the same mistake?

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

is problem E binary search?

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    10 months ago, # ^ |
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    I used ternary search

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    10 months ago, # ^ |
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    yes

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    10 months ago, # ^ |
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    yup. DP to calculate sum i -> j. then binary search

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      10 months ago, # ^ |
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      search over what

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        10 months ago, # ^ |
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        to find out K such that Math.abs(aL + a(L + 1) + ... + a(K) — U — 0.5) is Max

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          10 months ago, # ^ |
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          why does that function work

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            10 months ago, # ^ |
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            n = 1 => U

            n = 2 => U + U — 1

            n = 3 => U + U — 1 + U — 2

            ...

            n = m => U*m-(1 + 2 + .. + m-1) = U*m-(m-1)*m/2 = -1/2*m^2 + (1/2 + U) * m.

            It max when m = 1/2 + U

            => find K such that aL + a(L + 1) + ... + a(K) closest to m or 1/2 + U

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              10 months ago, # ^ |
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              yeah sorry you're right, I misread the problem statement. shit. this is so much easier than what I was tryna do

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    10 months ago, # ^ |
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    I was able to do it using binary search

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    10 months ago, # ^ |
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    yes, binary search on convex function.

    you can see my code for reference:

    problem E solution
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      10 months ago, # ^ |
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      its just a linearly increasing function.. the score is the convex function... only the index is needed so you can just use binary search on prefix sums

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        10 months ago, # ^ |
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        yes i saw after the contest, did not realise it in heat of the contest, as I misread the problem wasted 1 hour on completly different problem.

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10 months ago, # |
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problem e was truly painful to implement

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10 months ago, # |
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can someone tell me where it is giving wrong answer 248621389

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10 months ago, # |
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I used logic similar to finding peak element in array. But got WA. Could anyone please point out the mistake in my code?

Submission : https://codeforces.net/contest/1933/submission/248632005

Edit : Found the mistake. I was subtracting a[low-1] instead of a[l-1] :(

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    10 months ago, # ^ |
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    Thanks for the hint and your code,I tried implementing using peak element concept, but got stuck in the code, actually I did not initialize my ans to l and also did not make neighbour= -INF if they did not exist and your code came to my rescue.

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10 months ago, # |
  Vote: I like it +34 Vote: I do not like it

It was a good bluff to require us to answer modulo 998244353 in problem G. (I intuitively knew that the answer could not be large given the harsh conditions, but because of this requirement, I was not sure of my consideration that there are at most 8 patterns even after writing an experimental code with a brute force.)

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

great contest! i really enjoyed A,B,C,D,E, but couldn't implement bs in E, I need to practice more bs problems( Anyway great contest!

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10 months ago, # |
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anyone can explain the test case in problem G ?

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10 months ago, # |
← Rev. 2   Vote: I like it +4 Vote: I do not like it

Um_nik has uploaded a video about solving this contest before the contest ended: https://www.youtube.com/watch?v=Asqk4kXi8os&ab_channel=umnik_team . Will this contest unrated?

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    10 months ago, # ^ |
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    There is no point in making the contest unrated. Cheating happens and solutions get leaked on Telegram and YouTube in every contest.

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      10 months ago, # ^ |
        Vote: I like it +2 Vote: I do not like it

      But this is a public solution from a LGM while the contest is running. Anyone can AC all 7 problem with this video.

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        10 months ago, # ^ |
          Vote: I like it -6 Vote: I do not like it

        I dont think link was public during the contest.

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    10 months ago, # ^ |
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    I think it should be unrated because there used to be cheating to some level but this is not done, i was able to solve 4 in div 3 which is good enough, still suffered 44 rating decrease because of soo many cheaters. Ratings should be rollbacked for this contest. This was too much!

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10 months ago, # |
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Brooooo my stupid "print" statement costed me PROBLEM-C ripppppp

print
without

This could have been the greatest clutch of my life but NOPE. I want to jump off a cliff :((

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10 months ago, # |
← Rev. 3   Vote: I like it +26 Vote: I do not like it

Hints for all the problems before the editorial comes out.

A: Collect all the negatives in one subarray.

B: Maximum answer can be 2. Think about the cases when 1 and 2 will be answer.

C: What if we fix values of (x, y)? Also, the value of k will not be always distinct.

D: What if you keep minimum element at first? What if there are multiple minimums?

E: The sum is increasing upto a point and then it decreases. It starts decreasing after the (u + 1)-th section.

F: Firstly, coming at the same position again is not optimal. Secondly, we don't need the UP move until the last column.

G: Constructive problem, try to come up with a pattern using second test of sample. Also, the answer can be max upto 8, ignore the modulo.

Thanks to the authors for some very interesting problems.

Spoiler
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    10 months ago, # ^ |
      Vote: I like it +44 Vote: I do not like it

    Happy to hear that you liked F a lot (I wrote it) Thank you very much you have made my day.

    Hopefully, I don't get downvoted by saying this... ik this task kinda was a nightmare at first sight for some of you, but hope it was an interesting and insightful task. Hope it wasn't that hard to understand as well, I already tried to draw better graphics for the explanation.

    Anyways, we will try to get the editorials out as fast as possible :)

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      10 months ago, # ^ |
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      Keep up good work making problems interesting to think about and easy but not boring to implement.

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      10 months ago, # ^ |
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      No no, I think it was fine for everyone. And, the graphics were actually cool.

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      10 months ago, # ^ |
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      I really liked F :> Might even take inspiration from it to create some educational DP problems myself

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    10 months ago, # ^ |
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    hi, about problem F, do we really this observation to come up with a solution,

    "Secondly, we don't need the UP move until the last column."

    I think we can use simple bfs to reach the end

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      10 months ago, # ^ |
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      The observation is correct, but there are also other ways to realize such an observation which will be mentioned in the editorials. Of course there might be alternate solutions that also work, but having this observation does simplify the question a lot and can be done through dp or bfs.

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        10 months ago, # ^ |
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        yeah, I do know that, just wanted to know if someone solved this by just first obs,

        from each point, we move to three possible cells(up, down, right), using bfs we find the ans for last cell

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    10 months ago, # ^ |
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    In problem C, Why I am getting TLE in this code. It is O(max(13,sqrt(100))+ 3*10^3) .

    My submission

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      10 months ago, # ^ |
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      You forgot to add the complexity of creating a 10^6 sized vector in each testcase.

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        10 months ago, # ^ |
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        Thank you. I realised that I don't need to create those arrays .

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    10 months ago, # ^ |
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    In E, how can you say that the sum is a convex function?

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      10 months ago, # ^ |
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      you may have misread the problem description just like i did. among tracks the decline by one continues.

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    10 months ago, # ^ |
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    Could you please explain why we dont have to use the UP move until the last column, it will be very helpful

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      10 months ago, # ^ |
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      When you're doing the UP move, your position relative to stones isn't changing, so basically the whole setup is same in a rotational manner. The only thing that changes is relative position of ending cell, which you can also change when you're in the last column.

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    10 months ago, # ^ |
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    someone explain what does it mean by seeing the grid in the pov of grid? Everyone says see the grid as static? Someone kindly explain

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10 months ago, # |
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Is this one about turtles?

Every question is about a turtle.

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    10 months ago, # ^ |
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    Originally we had a storyline, but it was decided to be removed in the end to improve the task's clarity. The idea came from a few sources. The first one is because the old workplace or "home" of my school's robotics team (I was the captain last year) was next to a turtle pond, and so I have a strong love for turtles :) FYI, each of the teachers having their seats next to the pond were also called turtles with different nicknames for each of them. The second reason was that we liked Master Oogway in the movie Kung Fu Panda, so we thought it would be a good choice to use it as a theme, both silly and inspirational.

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10 months ago, # |
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Don't know! Should I be motivated or demotivated?! after seeing the problem setters...:/)

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10 months ago, # |
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I could not even solve B. Every one here is discussing about problem E

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10 months ago, # |
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Problems: Turtle

Editoral: Rabbit

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10 months ago, # |
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W contest , W younglings who made these questions ,Hope its not gone to waste cause of the stream upload

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10 months ago, # |
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Can anyone give any counterexample where this submission 248545787 doesn't work for C?

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10 months ago, # |
  Vote: I like it +5 Vote: I do not like it

fastest editorial ever seen

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10 months ago, # |
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I performed well in this contest but the contest is unrated for me because I became exactly 1600 after the rating roll back.

If I was 1599 I got +70 at least :)

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10 months ago, # |
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https://codeforces.net/contest/1933/submission/248622479 can anyone tell me what is wrong with this code for problem E

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10 months ago, # |
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.

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    10 months ago, # ^ |
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    If this is true I think CF can spot cheaters and skip them. so no worry :)

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    10 months ago, # ^ |
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    i mean people always post the solutions on youtube while the contest is running and have alot of views as well. i don't understand why when umnik do it it will be unrated , F and G don't have a lot of ACs anyway.

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      10 months ago, # ^ |
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      [deleted] it's not intentional ,it's a mistake and he apologized

      Edit: it was a great contest ,hope to see more such contest from authors

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        10 months ago, # ^ |
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        nvm

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          10 months ago, # ^ |
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          Few stupid guys!=whole india Stop using "Indians" "Russians" "Chinese" Do you compare umnik with this guys ? Definitely not

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            10 months ago, # ^ |
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            ok buddy I'll edit the comment and remove indians since this annoyed a lot of people.

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              10 months ago, # ^ |
              ← Rev. 4   Vote: I like it +1 Vote: I do not like it

              No hate bro ,what you said is correct there is a mass cheating in every contest and we can't stop them

              I know that umnik is not one of them

              but we can't judge a country by some brainless individuals

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10 months ago, # |
← Rev. 3   Vote: I like it +13 Vote: I do not like it

really liked both F and G, they are great! though $$$n, m \geq 5$$$ and strong sample little bit spoiled main idea of problem G, IMO.

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    10 months ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    I guess n = 3 and large m is way harder than the current problem, thus they made such constraints.

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10 months ago, # |
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Please don't make this one unrated:(

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10 months ago, # |
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In C, l could have been much larger.

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10 months ago, # |
← Rev. 4   Vote: I like it +11 Vote: I do not like it

UPD2: Since the editorial is not out yet...

A solution
B solution
C solution

Original Post: Solved ABCDEF and I had no non-trivial idea for G. I enjoyed this problemset, and DEF are good problems in my opinion.

D solution
E solution
F solution

UPD: G upsolved. The ST was slow and I submitted 1 hour after finishing coding.

G hint 1
G hint 2
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    10 months ago, # ^ |
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    Please tell me what is wrong with my implementation of E. I can't think of anyother way to implement it and also cannot make this implementation work. 248638966

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      10 months ago, # ^ |
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      why are you going up to u+1?

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        10 months ago, # ^ |
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        I may be wrong about it. Is that the issue ? I tried submitting with critical = u which also doesn't work.

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          10 months ago, # ^ |
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          if two index that are adjacent make same answer then you should take the lowest one. I think in the first test case your answer is giving wa. 3 1 4 1 5 9 for l = 1 and u = 8 your code gives r = 4. But r = 3 also gives the maximum sum. You should go upto u and check the next index also which is res+1. if it makes greater sum then output res+1 otherwise output res.

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            10 months ago, # ^ |
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            see my solution.

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            10 months ago, # ^ |
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            Now I got it, thanks a lot. I thought of checking neighbouring elements to the r that I found, also but it felt very hacky to me and did not try it even once. :(

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    10 months ago, # ^ |
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    Good hint for F. I was able to code it up after looking at your hint

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    10 months ago, # ^ |
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    begin with other elements, and you will get 0 at the first x. can you explain this with proof? Thanks in advance

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      10 months ago, # ^ |
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      Proof
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    10 months ago, # ^ |
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    For Problem-F

    Can you please help me :

    lets say that we reached the cell a[i][m-1] ...

    Why currAnswer = dist[i][m-1] + abs ( n-1 -i ) is not correct ?? ( where dist[][] can be found by simple BFS ) and thus the final answer will be Minimum over all i...

    How to correct it ?

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      10 months ago, # ^ |
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      What if you walk down and there are rocks in your way? The "wait" is to go up all the way(i.e. stay in place from the grid's viewpoint)

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10 months ago, # |
  Vote: I like it +13 Vote: I do not like it

The best insane problem D ever !!

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10 months ago, # |
← Rev. 2   Vote: I like it +4 Vote: I do not like it

Great Contest

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10 months ago, # |
  Vote: I like it +1 Vote: I do not like it

Please don't make contest unrated. Just check for plagiarism for problems E,F,G that were send last 30 minutes with the umnik's code from youtube.

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10 months ago, # |
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in prob C https://codeforces.net/contest/1933/submission/248626484 I am getting wrong answer from codeforces judge but if I am testing the wrong test case on my local machine it's giving me the right answer? WA on test case 2 40th test 8 4 780

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10 months ago, # |
  Vote: I like it +10 Vote: I do not like it

why Um_nik why

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10 months ago, # |
  Vote: I like it +2 Vote: I do not like it

The contest was very interesting, thanks to the organizers of the contest. I just found this stream where Um_nik broadcast the last ~1 hour of the contest. I felt very sad because some of the participants cheated and one of the great codeforcers has ruined contest. In fact, it's not about cheating, but about respect for the creators of the contest.

Dear organizers you did really greate job!

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10 months ago, # |
  Vote: I like it +69 Vote: I do not like it

heres why i solved this G 2x faster than rainboy.

https://imgur.com/dKUPRJ3

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10 months ago, # |
← Rev. 2   Vote: I like it -20 Vote: I do not like it

sirs

thank u the much for this roudn !!

but fapipitito notice G is pretty specil?? fapipotato confused !!

fapipotato find solution near end but cannot code fast be cause hand weakk :((((

i liek all problom and this very high qualiti round!!

mcuh love and look forward to more future later round from u guys!!

fapi potato

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10 months ago, # |
← Rev. 3   Vote: I like it 0 Vote: I do not like it

:)

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10 months ago, # |
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Really Great Problemset!

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10 months ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

I did a BFS implementation in Problem F. Sadly, I got a TLE on Test 12. Can someone point out how to avoid it from my code?

Code
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    10 months ago, # ^ |
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    I did same. i did not observe that robot will move up only in last column :(.

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    10 months ago, # ^ |
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    so move up only in last column will reduce your time complexity from O(n*n*m) to O(n^m)

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      10 months ago, # ^ |
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      Ohhh man. This ignorant habit of mine just sucks af! :") Thanks btw.

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10 months ago, # |
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Um_nik you are very bad

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    10 months ago, # ^ |
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    Everyone makes mistake

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      10 months ago, # ^ |
      ← Rev. 2   Vote: I like it +20 Vote: I do not like it

      I guess Master Oogway's words work again, "There is always something more to learn. Even for a (Legendary Grand) Master" lol.

      And despite such issues may be problematic, I think we shouldn't put all the blame onto Um_nik as him doing his videos were for a good cause in teaching programming, just that he may have accidentally posted it early. Additionally, he has already apologised as well and I agree everyone makes mistakes, me included. Hopefully, such issues will be prevented in the future. :)

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        10 months ago, # ^ |
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        but one thing i would say, umnik got really good taste in music xD!

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10 months ago, # |
  Vote: I like it +3 Vote: I do not like it

Problem F is Awesome.

A bit different from usual problems.

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10 months ago, # |
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was stuck at e, but then saw huge num of ac in E, around 4500 solve, now really upset after seeing the comments.

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    10 months ago, # ^ |
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    e is still not hard despite the cheating . you just have to find the first sum that's bigger than u, using binary search and find what's bigger this value or the one behind it

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      10 months ago, # ^ |
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      True. E was easy, but as i become super saiyan level dumb durning contest, i forgot to check the values behind

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        10 months ago, # ^ |
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        it happens don't worry . keep grinding

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10 months ago, # |
← Rev. 2   Vote: I like it +3 Vote: I do not like it

Problem F: BFS with one tricky observation. In this problem, the robot will move upward only when it's in the last column. Due to this constraint, the straightforward Depth-First Search (DFS) approach might lead to Time Limit Exceeded (TLE). This optimization should help improve the performance and prevent TLE.

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    10 months ago, # ^ |
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    I tried DFS, but getting WA 248632066. Any possible reason you could tell?

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      10 months ago, # ^ |
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      I haven't viewed your code but I don't think DFS will work, because BFS guarantees the lowest depth when each node is first visited but DFS does not

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        10 months ago, # ^ |
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        You don't need to ever revisit any cell, so it doesn't matter BFS or DFS. AC with DFS

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          10 months ago, # ^ |
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          You have to revisit cells if you are doing DFS and what you have linked is BFS

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            10 months ago, # ^ |
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            Whether it is a B of D FS is determined by the order of traversal, and not the function name or use of recursion.

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              10 months ago, # ^ |
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              Okay, the order of traversal in your linked solution is bfs order and if it was dfs order , you would need to revisit cells
              does this satisfy your highness?

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                10 months ago, # ^ |
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                No, because it's untrue

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                  10 months ago, # ^ |
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                  my bad. didn't realise your 'q' was not a queue but a vector

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10 months ago, # |
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Can anyone tell why my code for E is giving TLE on 8th TC after applying Binary Search. 248643885

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10 months ago, # |
  Vote: I like it +13 Vote: I do not like it

Can anyone try and hack my submission for F? I just did a O(n^3) BFS and used bitset to store visited. It passed somewhat comfortably but I'm wondering if there's a case where it blows up. https://codeforces.net/contest/1933/submission/248595937

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +11 Vote: I do not like it

    are u checking upward in all columns ??

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    10 months ago, # ^ |
      Vote: I like it +23 Vote: I do not like it

    Hacked.

    I generated a $$$1000 \times 1000$$$ grid with all $$$0$$$'s to greedily maximize the number of neighbors of each cell.

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    10 months ago, # ^ |
    ← Rev. 3   Vote: I like it +5 Vote: I do not like it

    I just added a condition where I move upward only in the last column and the runtime improved significantly, I don't think it can be hacked now. I think this implementation is very interesting because you are essentially doing the n^3 bfs with one little optimization for the transitions and the O(n^3) memory being reduced by a factor of 32 with bitset making it enought to pass the limits. https://codeforces.net/contest/1933/submission/248663273

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      10 months ago, # ^ |
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      bitsets are so dumb bro if u were really that good u would've figured out something easier noobie

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        10 months ago, # ^ |
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        shut up bro

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          10 months ago, # ^ |
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          hey friend,

          just wanted to drop a quick note to say sorry for what went down the other day. i know i messed up and i feel really bad about it. didn't mean to hurt your feelings or make things awkward between us. i hope we can talk it out and move past this. let's grab a coffee or something soon and chat about it. again, really sorry, mate.

          take care, [Your Name]

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          10 months ago, # ^ |
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          Nah man , he is onto something

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      10 months ago, # ^ |
      ← Rev. 4   Vote: I like it +19 Vote: I do not like it

      I think with your new optimization the time complexity actually becomes $$$O(N^2)$$$, and your space complexity would be $$$O\left(\frac{N^3}{32}\right)$$$ as you have stated.

      Moreover, I noticed that with your new optimization you don't even need the 3rd dimension for the visit array, since I think you can arrive at cell $$$(i, j)$$$ only if the time $$$t \equiv i + j \quad (\text{mod } N)$$$. So, you can optimize the space complexity further to $$$O\left(\frac{N^2}{32}\right)$$$. (see https://codeforces.net/contest/1933/submission/248668841)

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        10 months ago, # ^ |
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        The time complexity is still technically O(n^3/32) as I need to initialize the bitsets, however your idea fixes that issue. The 100ms saved is most likely just due to the fact that there wasn't a need for so much data to be initalized.

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10 months ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

It was indeed a good round, I just hope it doesn't get unrated.

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10 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I almost gave up doing competitive programming. After 19 months almost I thought, let's start again. I was reading the explanation of test cases of problem B. And I Couldn't even figure out how that explanation matches the output. Suddenly I see a message popping up, saying there was an error in the explanation of Problem B. How could the problem setters or the testers miss such error I don't know. I was totally frustrated and couldn't even focus anymore sadly. Such a frustrating experience -.-

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    10 months ago, # ^ |
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    You should build up your mentality for competitives

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10 months ago, # |
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I hope the round doesn't get unrated.

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10 months ago, # |
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really thank you It was a good math contest Just remember from now on, this is Codeforce not MathForces

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10 months ago, # |
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Was this really a Codeforce contest, 4 math and number theory questions in a row

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    10 months ago, # ^ |
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    Most CP problems require math on some level. Maybe try learning it?

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      10 months ago, # ^ |
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      YES Most CP problems require math on some level. but all of them doesn't have math tag

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      10 months ago, # ^ |
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      oh bro Now I want to teach you something very friendly In Codeforce, tags are set for many questions that show the key ideas of the solution and the algorithms necessary for the solution. So it's better to learn how to use this site before you come and comment

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10 months ago, # |
  Vote: I like it 0 Vote: I do not like it

help in problem C

here L = k * a^x * b^y, so, K must be a divisor of L. Now i need to check which of the divisors can be represented in (a^x*b^y) and count them. What is wrong with this idea? i think it shouldn't give TLE. My Source Code (WA on test 2)

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    10 months ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    Try putting your "k" values in a set. Maybe that helps.

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    10 months ago, # ^ |
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    You can keep the K values in hashmap for quick checking.

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    10 months ago, # ^ |
    ← Rev. 4   Vote: I like it 0 Vote: I do not like it

    In the code, you are only considering the case where a^x==l, or (b^y)==(l/a). Instead of thinking for 'k', try to generate all the values of (a^x + b^y) and then check if it divides l. Store the value of corresponding 'k' in a map or a set if it does. To avoid overflow issues you will need to consider the values of 'x' and 'y' up to which a^x and b^y do not exceed 'l'.

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10 months ago, # |
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Thanks for making the round rated.

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10 months ago, # |
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Thanks for problem E, I finally learnt how to implement ternary search.

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    10 months ago, # ^ |
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    What's the idea?

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      10 months ago, # ^ |
      ← Rev. 2   Vote: I like it +3 Vote: I do not like it

      My answer won't be perfect, but I hope you understand something.

      Spoiler
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10 months ago, # |
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A bit sad that I couldn't code the E problem in time, the prefix sum and a binary search was an obvious idea of the solution. Good contest tho, I assume that it is a perfect example of a well elaborated div3 round. Many thanks to the authors, it was a pleasant adventure!

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10 months ago, # |
  Vote: I like it -8 Vote: I do not like it

Child labor... unbeliavable.

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10 months ago, # |
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why trivial binary search not working on E! like lower_bound(pref.begin(), pref.end(), pref[l] + u) AAAAAAAAAAAAAAAAA!!!!

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    10 months ago, # ^ |
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    i mean that's literally my ac solution so idk bout you

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    10 months ago, # ^ |
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    you also need to think about the r+1 and r-1.

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10 months ago, # |
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https://codeforces.net/contest/1933/submission/248653337

Why my this solution is not working for E? im checking mid and mid+1

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10 months ago, # |
← Rev. 2   Vote: I like it +8 Vote: I do not like it 
#include <iostream>
using namespace std;

int main() {
    cout << "1\n"; // End the line after printing "1"
    cout << "1000 1000\n"; // End the line after printing "1000 1000"
    for(int i = 0; i < 1000; i++) {
        for(int j = 0; j < 1000; j++) {
            cout << "0 "; // Print "0 " without a newline
        }
        cout << "\n"; // End the line after printing each row of zeros
    }
    return 0;
}

I am trying to hack Problem F using above generator. But got this Verdict "Validator 'validator.exe' returns exit code 3 [FAIL Expected integer, but "#include" found (stdin, line 1)]". Someone help me find the error.

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    10 months ago, # ^ |
      Vote: I like it +31 Vote: I do not like it

    You have to find and use the "generated input" tab in the hacking interface.

    Besides that, you have to NOT print the trailing space in each line. Your test will be validated and then given to contestant, who doesn't have the obligation to work on malformed input. The validator does not fix formatting for you, it just reports that formatting is wrong (easier this way).

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10 months ago, # |
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I think my code is wrong in problem D 248569476 can someone hack it

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10 months ago, # |
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Thanks for keeping the round rated ❤️. It will encourage honest participants who invested their time in participating in this contest.

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10 months ago, # |
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"Round is still rated"

Lets goooooooooooooooooo

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10 months ago, # |
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You know u cant detect cheaters they can simply change the code u might find some but still its kinda unfair

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10 months ago, # |
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really enjoyed G and F. I don't know why I wrote a dfs solution for F during contest(that was also wrong).

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10 months ago, # |
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any hints for $$$F$$$?

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    10 months ago, # ^ |
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    You can remove the motion of the rocks by moving your reference frame up one unit each time step. From this point of view, at each time step the robot can either stand still, move down and to the right (if there is no rock at the end of this move), or move down two units (if there is no rock at the end of the move or at the intermediate square.) This may make it easier to see which squares the robot can reach and when it can reach them.

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10 months ago, # |
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Hints for G?

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    10 months ago, # ^ |
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    Answer is at most 8, try to write a bruteforce for n=m=5 and observe patterns.

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10 months ago, # |
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Thanks for the great problem F!

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10 months ago, # |
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Thank you guys for an amazing Div3!

Wow, the system testing is earlier than usual!

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10 months ago, # |
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Indian youtubers?

No, Um_nik

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10 months ago, # |
  Vote: I like it +30 Vote: I do not like it

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10 months ago, # |
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in Problem 'D', i used Unordered_map to save time and got TLE on testcase 30 ;(

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10 months ago, # |
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my program got TLE because use unordered_map? 248557195 (problem D)

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10 months ago, # |
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I think that there's a problem of rank updating ychaaibi rating ( 1406 )

Thanks in advance, also thank you for the contest.

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10 months ago, # |
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1599 after rating update. :( Does the rating increase after plag check is done?

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    10 months ago, # ^ |
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    Yeah the rank was updated and my rate was also increased by 3 ( 1406 -> 1409 )

    Thank you so much.

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10 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Thank you to the question team for providing this tournament making it possible for me to pass 5 questions during the tournament. good bye pupil ， hello Specialist ：）

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10 months ago, # |
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Is there anyway to get editorial of the contests (when over) at one-place.

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10 months ago, # |
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In Question 1933C - Turtle Fingers: Count the Values of k,

Can anyone explain why do i need to iterate the values of x from 0 to (log(l)/log(a) + 1) ? Similarly i need to iterate the values of y from 0 to (log(l)/log(b) + 1) .

Why do i need to check for the last value (log(l)/log(a) + 1) ? Because anyway a power (log(l)/log(a) + 1) will be greater than l.

why does my solution fail when i iterate only till (log(l)/log(a)) ?

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    10 months ago, # ^ |
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    When you compute log(l)/log(a) using floating-point arithmetic, you get rounding errors, so the value you compute may be less than the exact value. To see this, use a custom test to run the following program, which attempts to compute $$$\log 243/\log 3$$$:

    Test program

    You will get not 5 but 4.999999999999999.

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10 months ago, # |
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Where is the editorial?

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10 months ago, # |
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10 months ago, # |
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I made the same mistake using ideone.com. Next time, I will be more careful. Please, do not reduce my rating. These ratings are very important to me. Please do not block my account or impose penalties. I assure you that I will be more sincere in the future.

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10 months ago, # |
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i was taking this contest in my school(not only this one) a place where lot of computers are place there were many people that were taking this contest simultaniasly
due to my strategic of taking exams and contest , i have breaks through the exam time and it includes changing my position , having some fresh air , eating something , .... i believe when i was walking outside , someone has checked on my computer for codes of contest and because there are schools property , i can not put passwords on computers for security i will be sure that nothing like that will happen again

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