Vladosiya's blog

Codeforces Round #925 (Div. 3)
By Vladosiya, history, 10 months ago, translation, In English

Hello! Codeforces Round 925 (Div. 3) will start at Feb/13/2024 17:35 (Moscow time). You will be offered 6-8 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have a rating of 1600 or higher, can 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.

You will be given 7 problems and 2 hours and 15 minutes to solve them.

Note that the penalty for the wrong submission in this round is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. 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.

Problems have been created and written by our team: myav, Gornak40, senjougaharin and Vladosiya.

We would like to thank:

  1. MikeMirzayanov for help with ideas and Polygon and Codeforces platforms.

  2. nigus for red testing.

  3. vladmart, Gheal, KseniaShk for yellow testing.

  4. htetgm for purple testing.

  5. natalina, SashaT9, lockdown, bma20006 for blue testing.

  6. RedDreams for cyan testing.

  7. the_Incharge, Aurora__, Longqiang for green testing

Good luck!

P.S. Happy Valentine's Day!

UPD: Let's continue streak of announces with photo of the authors :)

UPD2: Editorial

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

Wow, you put a lot of effort to make a lot of quality div3. Thanks for a lot good div3 round to help beginner to advances in CP.

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

$$$\mathtt{Thanks \ for \ Legendary \ Div.3 \ Rounds , Looking \ forward \ to \ join \ the \ authoring \ forces}$$$

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10 months ago, # |
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Yeahhhh!!! Div 3 Letsssss Gooooo

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10 months ago, # |
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Div 3 are my favourite. Lots to learn.

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10 months ago, # |
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the round number and date is wrong please fix

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10 months ago, # |
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the round and date are wrong

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

speedforces let's go

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10 months ago, # |
  Vote: I like it +4 Vote: I do not like it

Thursday, October 12, 2023?

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10 months ago, # |
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I hope this is my last round before cyan

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10 months ago, # |
  Vote: I like it +54 Vote: I do not like it

Thank WHO for red testing 😳

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10 months ago, # |
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My first unrated Div3 I mog everyone

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10 months ago, # |
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Excited!! Hoping to reach pupil this time :)

UPD : FINALLY REACHED :)

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

don't make your gf sad, prepare gift after contest

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    10 months ago, # ^ |
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    cp and gf? nah man something doesn't feel right. Just don't touch grass and stay home I guess

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

I had no idea authors could be so pretty. I'm blushing (,,>﹏<,,)

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

    mmm, why?

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

      I was hoping the authors would see it and feel happy.

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

        No, I mean why you thought that authors couldn't look pretty. As far as I'm concerned they're all human beings, just like the rest of us

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          10 months ago, # ^ |
            Vote: I like it +9 Vote: I do not like it

          If I became an author, I would be a good counter-example :)

          But you are correct. Everyone is beautiful. That's why its great to have pictures of the authors in the announcement.

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

so sweet post. Happy Valentine's Day. Do spend time with ur loved ones, instead of attending contests

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10 months ago, # |
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Can you pin social media handle (Instagram) of girls in image, i need tips for CP from them :)

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10 months ago, # |
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I am the one in the button right on Valentine's day :⁠,⁠-⁠)

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

I don't get it,why are authors making a 'C' with their hand?

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    10 months ago, # ^ |
      Vote: I like it +26 Vote: I do not like it

    May be because Mike also did the same on his picture (to hold the burger)?

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    10 months ago, # ^ |
      Vote: I like it +33 Vote: I do not like it

    It's not the letter "C", it's half a heart (we tried, ahahah) We wish the community a happy Valentine's Day!

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      10 months ago, # ^ |
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      Got it,that makes sense,i need to go out and meet some real people.

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10 months ago, # |
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Thanks for the contest but why y'all throwing up gang signs?

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    10 months ago, # ^ |
      Vote: I like it -14 Vote: I do not like it

    Bro failed to get some contribution XD

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      10 months ago, # ^ |
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      Lol, at +116, even 100 upvotes on this comment won't change my contribution at all

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10 months ago, # |
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Valentine's Day ? Oh man, i am CPer

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10 months ago, # |
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Wow, this is great.

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10 months ago, # |
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Looking forward to it!

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10 months ago, # |
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My first unrated contest

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10 months ago, # |
  Vote: I like it +90 Vote: I do not like it

They are so similar

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10 months ago, # |
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why are the names of the authors written in reverse

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10 months ago, # |
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I really hope to become Pupil in this contest.

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10 months ago, # |
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Hopefully my last rated div3

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10 months ago, # |
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Wish everyone will have a good score!

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10 months ago, # |
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why the solution will be out 5 minutes before the contest ends?

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10 months ago, # |
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Hope positve delta for all rated participant.

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10 months ago, # |
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Finna reach 1000 elo ;))

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10 months ago, # |
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I'm really looking forward to the Codeforces contest taking place tonight, on the fourth day of the Lunar New Year. It's an exciting opportunity to challenge myself and improve my problem-solving skills！

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10 months ago, # |
  Vote: I like it +20 Vote: I do not like it

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10 months ago, # |
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NOOOO THE CONTEST END 10 MINUTES AFTER MY OLYMPICS(school)

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10 months ago, # |
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Good luck to everyone.I hope to become expert on this round.

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10 months ago, # |
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Hoping to solve atleast 2 problems this contest

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10 months ago, # |
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Iam ready to solve just one problem As usual

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10 months ago, # |
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Thank you

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

Hope to reach expert again

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10 months ago, # |
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hope to be specialist,,if i could solve E, my day will be great otherwise it gonna worse,,,

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10 months ago, # |
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I give up more than an hour trying to figure out B and its just not working

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    10 months ago, # ^ |
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    same here... i dont know what are the mistakes i am doing as A,B,C all the three questions are very easy

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10 months ago, # |
← Rev. 2   Vote: I like it -13 Vote: I do not like it

Disgusting problem F

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    10 months ago, # ^ |
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    It's not, F is basically "Detect cycle in a directed graph".

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    10 months ago, # ^ |
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    you can do "F" just by making first line as 1, 2, 3, ... n, and these ai changes in next k — 1 lines too.

    Then for each line just check order is maintained (i.e. curr element is less than last)

    As an edge case: ensure "1" is correct in all.

    submission

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10 months ago, # |
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I absolutely clutched problem E with 10sec remaining!!

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10 months ago, # |
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Got the right idea for F about an hour after the contest started but spent the next hour debugging double-hash. :(

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    10 months ago, # ^ |
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    Hope no one tries to hack me after I write this comment. :(

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10 months ago, # |
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please hint for C

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    10 months ago, # ^ |
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    Try to fix equal element, either equal element can be first element of the array or last. Then find the range i and j

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    10 months ago, # ^ |
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    You MUST choose x as the first OR the last element.

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    10 months ago, # ^ |
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    three possible ranges you will select from k to n , from 0 to n-k , or from i+k to n-k. k is the index is where there's no more duplicates from the beginning or end from the array, like [1,1,1,2,3,4,5] k is at index were ai is equal 2 , so we can make the range we select [4,7] , same from the back. i+k to n-k is when the duplicated at front is the same from the back . sorry for bad explaining

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      10 months ago, # ^ |
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      i did that but test case number 2 gives WA 246226405

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        10 months ago, # ^ |
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        Same problem, everything seems right still tc2 shows wrong, 112th answer being wrong by 1.

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    10 months ago, # ^ |
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    You can look for the longest segment of equal elements from the start, let's call it a, and the longest segment of equal elements from the end, call that b. Now, there are two cases:

    (1)If the first and last elements are equal, you can choose the contiguous segment of elements not in either a or b. (notice, if len(a) + len(b) > n, the answer is zero. Else the answer is n — len(a) — len(b))

    (2)If the first and last elements are not equal, you choose the equal element as the element that comes in the longer segment. (notice, the answer in this case is n — max(len(a), len(b)))

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10 months ago, # |
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The CloudFlare feature is really a shit ,can't submit the solution even after doing it

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10 months ago, # |
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i am annoyed i couldn't get F i didn't think it will be cycle detection at all.

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10 months ago, # |
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Problem D is nice, thanks for the contest. But how to solve F?

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10 months ago, # |
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I feel like idea of F was simple but the implementation was tedious. Also, loved G!

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10 months ago, # |
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Any hints for G?

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

    Try reducing this problem to a stars and bars problem Try to think what are the prerequisites if we want to place the 4th block at any place same goes for the 3rd Think which blocks are the limiting factors and which we can take care of irrespective of their quantity Have a Great solve!!

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

Maybe it's just me, BUT F seemed way easier than both D and E, although didn't spend much time on E after I saw F, which I had just the right idea for. Overall very fun Contest.

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10 months ago, # |
← Rev. 2   Vote: I like it +25 Vote: I do not like it

Quick hints for all the problems before the Editorial comes out.

A: Just brute force on each index using 3 for loops.

B: As the water can't flow backward, therefore the amount of water in any prefix can only decrease or stay constant.

C: Check if all equal, else count prefix equal length and suffix equal length.

D: What if we store the remainders in pair<int, int>?

E: Replace each number by the count of its trailing zeroes, now play the game greedily.

F: We can easily create the order from the first 2 arrays given (if k = 1, then its YES). Just make sure to handle one edge case [1,2,3,5,4] and [2,1,3,5,4], basically those in which there are 2 possible orders)

G: Pieces 1 and 2 can only appear alternatively, and the pieces 3 and 4 will always fit in the between their occurences. Also, pieces 3 and 4 can be repeated, while 1 and 2 can't. Try fixing Piece 1 or 2 as the first piece in the chain, do you get some general pattern?

Spoiler
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    10 months ago, # ^ |
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    Simple way to do F

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      10 months ago, # ^ |
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      Easier way to solve F without using graph

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      10 months ago, # ^ |
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      Yeah this subproblem looks way more easy and familiar, I was just hasty and went with my first thought.

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    10 months ago, # ^ |
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    In F, I think the simplest way to code is model it as a graph and use topo sort. I think that makes implementation really easy with template :)

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      10 months ago, # ^ |
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      F feels like AtCoder style problem, doesn't it? :)

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        10 months ago, # ^ |
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        I think it's more like the first few problems of a regional.

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    10 months ago, # ^ |
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    can up please tell what's wrong with this

    code
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    10 months ago, # ^ |
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    I did F after constructing the graph and checking if the number of SCC is equal to $$$n$$$:)

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      10 months ago, # ^ |
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      can someone define the statement in a prettier manner? I can't understand that. I know how to do cycle detection but the statement itself is unclear.

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10 months ago, # |
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F — "Detect cycle in a directed graph."

Submission- 246203312

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10 months ago, # |
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can anyone share any hint for problem D?

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10 months ago, # |
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How to combine pieces in the second test case of problem G (one sample way would be enough, please)?

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    10 months ago, # ^ |
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    121212121244 or 121244121212

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      10 months ago, # ^ |
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      Hmm, but there are only 2 pieces of type 2 and single piece of type 1: c = [1 2 5 10]

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        10 months ago, # ^ |
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        Sorry I misread it as second last test case, for the 2nd tc, here is one,

        333332124444444444 or 333332444444444412

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          10 months ago, # ^ |
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          Thanks! Now I see why I could not solve the problem :)

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10 months ago, # |
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I just wanna say thank you for making this contest, I was able to solve till F( can't believe I did this )

I think I have very unique solution for problem D: Problem D Solution

I used modular operations for storing single value in map

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    10 months ago, # ^ |
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    I did not get the logic behind your code. int v = mod*a + b ; int fv = mod*fx + fy ; why did you do this?

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      10 months ago, # ^ |
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      For pair $$$(a,b)$$$ we interested in pair $$$((x-a)\mod{x}, b)$$$

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      10 months ago, # ^ |
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      this is a trick,

      for representing two number in single number,

      lets a , b are the numbers i want to encode it into one number, then i will choose mod > max( a , b )

      then encoded_number = mod*a + b

      when you want,

      to get b = encoded_number%mod ;

      to get a = encoded_number/mod ;

      so with one encoded_number i have stored two values

      EDIT: fixed formatting

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10 months ago, # |
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just 3 again

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10 months ago, # |
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Code editor is not working, keeps running and no result, makes the whole experience shit. Cant run test cases.

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

How to solve G: https://chat.openai.com/share/3647110d-401a-4591-9dda-840260a0317d

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    10 months ago, # ^ |
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    you just calculating binomial coefficient, how is this related to solving G?

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      10 months ago, # ^ |
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      Because the only thing that came to my mind was:

      • place a 3 on this group (between 1 and 2),
      • or move to the next group

      which led me to the formula: $$$dp[i][j] = dp[i - 1][j] + dp[i][j - 1]$$$, and I didn't realize that it was effectively just comb(i + j, j), so that's what ChatGPT told me.

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10 months ago, # |
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https://codeforces.net/contest/1931/submission/246186250

The best solution to hack:)

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10 months ago, # |
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Here is how you can choose the next type of element to add in problem G.

Two nice observations:

  • This condition must be satisfied: $$$\left|c_1 - c_2\right| \le 1$$$.
  • Think about the problem without elements of types $$$3$$$ and $$$4$$$, then try to insert them in the generated chains.
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10 months ago, # |
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When I saw other's solutions,I found the problem E very easy. However,I think F is easier than E because I can get the idea to solve it without thinking.(if you know something about graph)

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    10 months ago, # ^ |
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    I agree. I knew immediately I could use Khan's algorithm to solve F right after I read it. But the strategy for E took me some time. (and I solved F before E)

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10 months ago, # |
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I was wondering whether this contest gives any rating? I am 401 rated. I have participated and solved 2 problems but haven't got any rating. Can anyone tell me if i'll get any rating?

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10 months ago, # |
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Does the following work for F?

Rearranging any of the participants except the last one cannot change the last participant from the permutation. Therefore, we can find the real permutation by checking which one has the last participant only once. Now, that we have obtained the real permutation, we can compare all of the k inputs to the real one and check.

This doesn't work when k == 2 but in that case we can simply check subsequences ignoring the first two numbers.

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    10 months ago, # ^ |
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    Better Idea:

    Simply Ignore the first Position of Every observation. Take an edge pointing from v[i] to v[i+1] (1 <= i <= n-2) for Every participant observation.

    Check for the cycle in the graph, If the cycle exists then NO else YES.

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      10 months ago, # ^ |
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      How to check if a cycle exists? I tried doing it using DFS but it exceeded the time limit.

      246185460

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        10 months ago, # ^ |
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        check this blog detect cycle in directed graph

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          10 months ago, # ^ |
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          Thank you!

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            10 months ago, # ^ |
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            TLE coz of MAX maybe, You are unnecessarily assigning 2e5+7 values to the array, even when N = 1.

            Just imagine for the test case where t = 10^4 and N for each case belongs to {1,2,3,4,......2e5}, even if k = 1.

            As this test case fits under the given constraints, You will be doing 2e5*(1e5)/2 roughly around 1e10. That's y.

            I think so, I can be wrong.

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              10 months ago, # ^ |
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              Yeah, I think that was the problem. I just resubmitted resetting only n values and it got AC. Just missed it during the contest :(

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    10 months ago, # ^ |
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    246262272 Maybe hashing was unnecessary, also who knows if this might get hacked.

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10 months ago, # |
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Loved the beautiful Stars and Bars problem (G) Got to the solution but didn't submit earlier as I was unsure if it would be rated for me Nonetheless Here's my solution in case any one wants a reference: https://codeforces.net/contest/1931/submission/246256160 :)

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10 months ago, # |
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As an expert I failed D: TLE on test 9. Here is my code: 246198274. Could anyone help me with debugging? I think this is O(nlogn).

Edit: This is O(y). Forget it

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10 months ago, # |
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How to solve E? Didn't get any idea at all :(

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    10 months ago, # ^ |
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    1) Ans "yes" if number of digits in the last number >= m + 1. Anna in each step tries to reverse number with maximum zeroes on the end. Sasha in each step does concatenation number with maximum zeroes on the end with any number without zeroes on the end (number without zeroes on the end is guaranteed to exist, since it either exists initially, or Anna will make it her first move)

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    10 months ago, # ^ |
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    it is optimal for both of them to the choose the numbers which have most no. of zeros at the end

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    10 months ago, # ^ |
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    multiset<pair<trailing_zeroes, digits>> and just model a game

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    10 months ago, # ^ |
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    you can simulate it as follow: for anna reversing a numbers is equivalent to deleting the trailing zeros so she should take the number which have the most trailing zeros every turn for sasha she will also choose the number with most trailing zeros and concat it with any number (it doesn't matter but we can choose the second most number having trailing zeros for implementation purpose) by doing this it save the trailing zeros in the largest number so anna can't remove them by reversing the number thats it u can keep track of the numbers having most number of trailing zeros using a priority queue and update it each turn accordingly

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10 months ago, # |
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This is my first AKed competition, and the problems were wonderful and quality, thanks! I like G best, it's an interesting counting problem.

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10 months ago, # |
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FUN QUESTIONS, Extremely challenging but really good questions.

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10 months ago, # |
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Can someone please help me in Problem C?

I am not getting why it gives me wrong answer on test case 2 (112th answer in tc2 is wrong it says, and I am not able to see what that case is because after certain lines the input of test case just shows "...")

Here is the submission —

246248784

Thanks!

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    10 months ago, # ^ |
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    I dont know python so I apologize if I am wrong but if first and last element are equal then the ans should be 'n-(s+e)'

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      10 months ago, # ^ |
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      yes so in python ".strip()" will remove all occurences of the passed argument from the front AND the back ONLY(not in the middle). So that part works alright.

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        10 months ago, # ^ |
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        Have you considered striping the last part too?

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10 months ago, # |
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I think you should reduce the time limit of this problem. this submission -> https://codeforces.net/contest/1931/submission/246247517 runs in 1 second. this submission should not get AC because # of testcase is 10000 and this submission is executing a for loop of 200005 every test case. that's more than 2e9 operations.

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10 months ago, # |
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!What is this submission code
is he know the testcase?

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10 months ago, # |
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After successfully wasting 1.5 hour on B i smashed binary search in B

can someone hack it?

246247536

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    10 months ago, # ^ |
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    why would you even think of binary search . you already know that the good value is sum/n . that's the only way you can make tha array the same

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      10 months ago, # ^ |
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      yeah i am dumb. do not know why that did not come into my mind

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        10 months ago, # ^ |
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        same here I thought of every thing in this life except that the only possible number is sum/n by the way I wanted to do binary search but I didn't know how to handle the good function but I learnt that from you now I mean the 1 , -1 and 0

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10 months ago, # |
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Video Editorial for problem B (Audio : Hindi) TUTORIAL VIDEO LINK

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10 months ago, # |
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Is this hackable B ? 246258951

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    10 months ago, # ^ |
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    I don't think so.. I used a similar approach so.. I hope it is not

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10 months ago, # |
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Thanks to the authors for an interesting div 3 without clay and with tasks that are fun to solve. After this div and the Cognitive Technologies Olympiad, I realized that the name Gornak in the list of authors => good Olympiad/div.

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10 months ago, # |
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Can G be solved using inclusion exclusion ?

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10 months ago, # |
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May I ask why I passed 3 questions but didn't receive a rating in the end? Or who should I seek help from? I really want this rating, thank you.

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    10 months ago, # ^ |
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    Rating appears after 1 to 24 hours from the end of a contest, and if there is a hacking phase, like this contest, then it may last up to 24 hours or less.

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10 months ago, # |
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in Problem E , i wrote code which was absolutely right, the only thing i missed was, if number>=10^m then number of digits should be >=(m+1) not >=m (it was pretty close :) )

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10 months ago, # |
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I submitted E when there were 10 seconds for the contest to finish and my submission got vanished...

why so ?

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10 months ago, # |
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In Problem C anti hash test case can be created as many unordered map solutions have been accepted.

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10 months ago, # |
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How to solve Problem G?

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10 months ago, # |
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wow that was very cool

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10 months ago, # |
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A different way to do F:

  • Each element (after the 0th element in the kth list) can only be it's current position or its current position+1

  • Store both possibilities in a vector

  • Remove possibilities for elements when they're no longer possible (i.e. the current element's position in the kth list conflicts with the elements position in a previous list)

  • The answer is no if an element has no possibilities, or if its only possibility conflicts with another elements only possibility

  • Otherwise the answer is yes

Code: https://codeforces.net/contest/1931/submission/246250979

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10 months ago, # |
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I am getting wrong on test case 3 for problem E

My approach is " The first set contains numbers with leading zeros, while the second set comprises numbers without leading zeros. Within a while loop, the first element of the first set is removed, and its length is added to the second set. Additionally, the first value of both sets is combined and inserted into the second set. The game iterates until the first set is empty. Afterward, the sum of the lengths in the second set is calculated. If this value exceeds a specified threshold, Sasha wins; otherwise, Anna wins.

can anyone help me find what's wrong in this?Solution link

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10 months ago, # |
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really enjoyed this contest, particularly problem D. start to see some common patterns on int-mod problem..

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10 months ago, # |
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my respect to Aleksander Gornak

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10 months ago, # |
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I was getting runtime error (STATUS_ACCESS_VIOLATION) in E, during contest , but after contest when i submitted same solution it got accepted . runtime error during contest code link.
accepted code after contest. Thanks

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    10 months ago, # ^ |
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    The problem is this for loop here: for(ll i=vect.size()-1;i>=0;i-=2).

    In C++, the return type of std::vector::size is an unsigned integer. When vect is empty, then vect.size() - 1 becomes 0 - 1 which then overflows to UINT_MAX. This causes out of bounds error which is why your program got runtime error. (It seems that this is changed in C++20, which is why your other code got accepted)

    To fix this, you just have to convert vect.size() into any signed integer type. For example for(ll i=(ll)vect.size()-1;i>=0;i-=2). New code

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10 months ago, # |
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Video explanation of Problem G (Chinese)

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10 months ago, # |
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One of the best rounds I've ever participated. Thanks to all the writers and testers for offering us such a round.

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10 months ago, # |
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The best div3 round contest I've ever participated!Thank you!

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10 months ago, # |
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when will the rating come out?

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    10 months ago, # ^ |
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    you need to wait that the system testing ends first (is around 80% right now). after that eventually the rating will be updated.

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      10 months ago, # ^ |
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      Oh,Thank you.This is my first time to attend CF.(I find out my G turned out to WA,It used to be AC)

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        10 months ago, # ^ |
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        I saw it as a AC, when the system testing is running and your AC code is still on queue, if you had a WA before the AC, you will see as if you get a WA. So congrats on your first contest participation in CF was really good!

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        10 months ago, # ^ |
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        First CF got G AC,congratulations!

        I'm waiting the rating, too.

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        10 months ago, # ^ |
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        Thank you for your encourages!

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10 months ago, # |
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Can anyone tell me where have I made a mistake in these two codes? Only difference I have made from my side is making the capital N,small n? Basically I had initialised all visited array elements to zero in reset function. Thankyou in advance.

1st submission 246198873

2nd submission 246233252

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    10 months ago, # ^ |
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    I don't understand why exactly gives you another answer (actually I'm more curious of how didn't get you RTE hahaha weird stuff)

    But the reason why the change works is because in the WA submission, you have the following code:

    vi g[N];
void reset(){
	fr(i,0,N){
		g[i].clear();
		vis[i]=0;
		vis1[i]=0;
	}
}

    and fr is #define fr(i,a,b) for(int (i) = (a); i <= (b); (i)++)

    So, the cycle in reset() will access to the position $$$N$$$. But the arrays g, vis and vis1 are of size $$$N$$$, I change you code putting a -1 and now it gets TLE, that makes a lot of sense, because $$$t = 10^4$$$ and $$$N=2e5+69$$$, so you will do around of $$$2\cdot 10^9$$$ operations just to reset.

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10 months ago, # |
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In Question 4 this code exceeds time limit on test case 33 cant understand why its o(n) approach can someone please help me?

include<bits/stdc++.h>

using namespace std;

define ll long long

int main() { 

int t;
cin >> t;
while(t--)
{
    ll n, x, y;
    cin >> n >> x >> y;
    unordered_map<ll, ll> dp;
    ll a[n];
    ll ans = 0;
    for(int i = 0; i < n; i++)
    {
        cin >> a[i];
        ll f = (x - a[i] % x) % x;
        ll l = a[i] % y;
        ans += dp[f*y+l];
        dp[(a[i] % x)*y+a[i] % y] += 1;
    }
    cout << ans << '\n';
}
return 0;

}

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    10 months ago, # ^ |
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    Same happened with me many times... :(

    Its because of unordered_map if you use simple map it will pass....

    For more: https://codeforces.net/blog/entry/62393

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    10 months ago, # ^ |
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    Worst case time complexity of unordered map is o(n) while normal map is of o(logn) that's why it is giving Tle. I got AC with your solution by just changing unordered map to normal map

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10 months ago, # |
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But may I ask why I still haven't received a rating? It should have been a long time since the hack phase ended. I really want the rating for div3 this time, thanks.

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    10 months ago, # ^ |
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    You must wait for some more hours after the system test. Codeforces needs time to calculate rating changes. Just chill

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10 months ago, # |
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Why there is no rating change? My rating is less than 1600

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    10 months ago, # ^ |
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    It takes a while after the system test for codeforces to remove cheaters and recalculate the rating changes.

    By the way, have we met somehow before?

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10 months ago, # |
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can anyone just tell me which are valid patterns in G? I can't find any for 1 2 5 10

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    10 months ago, # ^ |
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    One of the valid sequences is:

    2 4 4 4 4 4 4 4 4 4 4 1 3 3 3 3 3 2

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      10 months ago, # ^ |
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      Thank you... I didn’t notice self loops.

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10 months ago, # |
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when it will be rated?

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10 months ago, # |
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All my submissions have been blocked due to one answer(246237190) for question 1931F being very similar to the ones given by two other people.

One of them is from another guy studying in my institute who happens to study from the same materials and has given similar contests, hence the answers are very similar. Please review it and I hope my submissions are considered.

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    10 months ago, # ^ |
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    This clearly is a very repeated question, since many people have the same solution Please review it once.

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      10 months ago, # ^ |
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      It is very clear that You have copied this code 246237190 from somewhere, you didn't even put the effort to indent it properly. I think it is justifiable to get blocked.

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        10 months ago, # ^ |
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        So your justification of me getting blocked is the code not being indented

        i was in a hurry, thats it

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        10 months ago, # ^ |
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        You know what Leave it, you and I both know how much ever I fight there isn’t going to be any change I better focus on future contests, even if they unjustly block me again I will create new account and start again

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10 months ago, # |
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Key observation of problem E!
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10 months ago, # |
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I am new to code forces this is my first contest, I have solved two questions still didn't get any rating. Did I miss anything?

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10 months ago, # |
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Hi, I participated in 925 and it wasn't rated for me, does anyone know why? I am < 1600 (878).

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10 months ago, # |
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Give me my rating pls((

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10 months ago, # |
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Finally blue. Was a great experience.

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10 months ago, # |
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Hi I attended this contest and I solved problems A & B and got D wrong. And i'm not able to find the constest under my contests and my rating afterwards didn't although I am under 1900. Can you please explain why my rating did not improve?

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10 months ago, # |
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Become a pupil from this contest.

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10 months ago, # |
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I am sorry for using a code snippet that is used by lot of other people. This made me into this trouble of making code solution identical to other users. I regret using this snippet now. I shall prevent myself from further using this snippet anymore. Sorry CF ...

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10 months ago, # |
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why aren't the ratings changing ? Its been 2 days

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10 months ago, # |
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Hello respected judges,

My code was accidentally matched with the other participants. I have no idea about this rule of the CodeForces of contests. I didn't know this before. I had no selfish intention to do this cheat of any type. That participant is my college friend, and we discussed not exactly but similar type question before this about how to solve it. But I didn't know how we both accidentally write up the same code.

So, please can you give me my rating back, in future I will take care of it and not publish my code publicly anywhere.

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    10 months ago, # ^ |
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    You mean your rating reduced?

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      10 months ago, # ^ |
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      No, my rating has not increased. My solved question which matches with others was skipped means not considered for evaluations.

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    9 months ago, # ^ |
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    lol

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      9 months ago, # ^ |
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      Happy Birthday to your alt account, just 2 minutes before re-registering on Codeforces. And hey, you're new here, aren't you?

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