IgorI's blog

By IgorI, 13 months ago, In English

Hi, Codeforces! Happy New Year!

I'm glad to invite you to Hello 2022, which will take place on Jan/03/2022 17:35 (Moscow time). You will have $$$2$$$ hours $$$15$$$ minutes to solve the problems. This round is rated for everyone.

All problems are authored by me. I would like to thank 74TrAkToR for excellent round coordination and MikeMirzayanov for great Codeforces and Polygon.

There can be an interactive problem in this round. Don't forget to read the guide on interactive problems.

The scoring is $$$500-1000-1500-1750-2250-2750-3000-3500-4500$$$.

Good luck!

Editorial

Thank you for participation! Congratulations to the winners:

  1. tourist

  2. maroonrk

  3. Radewoosh

  4. Benq

  5. djq_fpc

  6. mnbvmar

  7. ainta

  8. 244mhq

  9. ecnerwala

  10. Rebelz

Announcement of Hello 2022
 
 
 
 
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13 months ago, # |
  Vote: I like it +149 Vote: I do not like it

Happy new year

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    13 months ago, # ^ |
      Vote: I like it -129 Vote: I do not like it

    cout << Happy new year & Happy coding << endl;

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      13 months ago, # ^ |
        Vote: I like it +48 Vote: I do not like it

      sorry

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      13 months ago, # ^ |
        Vote: I like it +166 Vote: I do not like it
      main.cpp: In function ‘int main()’:
      main.cpp:5:9: error: ‘Happy’ was not declared in this scope
          5 | cout << Happy new year & Happy coding << endl;
            |         ^~~~~
      
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        13 months ago, # ^ |
          Vote: I like it +14 Vote: I do not like it

        That's life to u my friend

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

        Syntax is still fucked up even if it was declared in that scope.

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13 months ago, # |
  Vote: I like it +71 Vote: I do not like it

Happy new year to everyone!

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    13 months ago, # ^ |
      Vote: I like it -138 Vote: I do not like it

    cout << Happy new year & Happy coding << endl;

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

      Hello and happy new year to you too but encase it in double inverted commas as it is a string and using cout without fast i/o is not preferred by good competitive programmers ,if you don't wanna use fast i/o ,use printf instead .I guess that's the reason you were downvoted massively .

      UPD: Sorry i missed one more point ,you are using endl which is too slow as well ,use \n instead for your wishes to reach people as soon as possible

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

    Happy new year everyone and wish you happiness!

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13 months ago, # |
  Vote: I like it +296 Vote: I do not like it
Fun fact
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    13 months ago, # ^ |
      Vote: I like it +124 Vote: I do not like it
    Another fun fact
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13 months ago, # |
  Vote: I like it +29 Vote: I do not like it

Happy new year and hope a wonderful round!

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13 months ago, # |
  Vote: I like it +83 Vote: I do not like it

Happy new year!

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13 months ago, # |
  Vote: I like it +52 Vote: I do not like it

Happy New Year Everyone!

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

Hoping to break out of grey this year : D

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

HAPPY NEW YEAR Let's start this year with positive hopes

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

Happy New Year

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

Happy new year everyone, hope this 1st contest of the year brings more positive delta.

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13 months ago, # |
  Vote: I like it +22 Vote: I do not like it

Happy New Year! May everyone have positive deltas in this round!

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    13 months ago, # ^ |
      Vote: I like it +22 Vote: I do not like it

    Is it even mathematically possible?

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

      Maybe it's impossible, this blog says that "Choose a group of the most rated (before the round) participants and decide that their total rating shouldn’t change."

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

Happy new year everyone. Hope for a great year ahead.

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

Good luck to all competing!

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13 months ago, # |
  Vote: I like it -122 Vote: I do not like it

cout << Happy new year & Happy coding << endl;

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    13 months ago, # ^ |
      Vote: I like it +42 Vote: I do not like it

    Unfortunately ur red colour is also not helping u in upvotes

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      13 months ago, # ^ |
        Vote: I like it -36 Vote: I do not like it

      If you are shining and you will give some shine to others then, you will not lose your shining.

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

        It doesn't work that way with contribution boi

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13 months ago, # |
Rev. 2   Vote: I like it -27 Vote: I do not like it

cout << "With best wishes for A HAPPY NEW YEAR!\n";

cout << "Wish you all positive deltas in the competition!\n";

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    13 months ago, # ^ |
      Vote: I like it +95 Vote: I do not like it

    endl is too slow, use '\n' instead if you want to send wishes :)

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13 months ago, # |
  Vote: I like it +1 Vote: I do not like it
Happy New Year

Good luck for the 1st contest in this year.

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

Any guesses on the amount of problems?

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

Happy New Year! I didn't make any new resolution this year (previous years resolutions yet to complete)

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

Happy new year!

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

as a dark reader user i hate the snow in the background

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

Happy new year!

Hope my first contest will be wonderful!

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

Happy New Year for everyone

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

Happy new year..I hope everyone have positive deltas in this round!!

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

Happy New Year everyone!

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

Happy New Year!

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

Happy New Year everyone! Let's gain rating in the first contest of the year)

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

Happy New Year everyone!

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13 months ago, # |
Rev. 4   Vote: I like it +5 Vote: I do not like it

Happy new year everyone!

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

Happy New Year Everyone!

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

How many problems will be there ?

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

I'm excited for contest

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

Happy New Year! The amount of testers makes me sure that the first round of the year will be a good one.

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

Happy New year Everyone! (✿◠‿◠)

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

    I like your anime a lot (^▽^) Good luck and have fun!

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

      Glad you liked it, season-2 drops April 2022! ヾ(≧▽≦*)o

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

Happy new year

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

Score distribution ?

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

What are the degree of difficulty by the contest?

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

I am very excited for this round. !!

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

Getting back to giving contests regularly after a long time. (part of my new year resolution). All the best to everyone and me xD.

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

Codeforces comeback? There weren't any contest for the year!

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

happy new year all. |

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

is this contest suitable for div3's people?

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

2022!

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


Why 9 problems in 2:15 and not in 3 hours?

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

There are still more than 35 minutes left to register and the registration count is already above 24k... Seems to be like that the community is taking new year resolutions seriously... Happy to see this happening :-)

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13 months ago, # |
Rev. 5   Vote: I like it 0 Vote: I do not like it

.

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13 months ago, # |
  Vote: I like it +46 Vote: I do not like it

7 participants from top-6

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13 months ago, # |
  Vote: I like it -134 Vote: I do not like it

MikeMirzayanov, I know that this is not the right place to write this but the false positive against my solution for Problem A of Goodbye 2021 still hasn't been reverted. I haven't even got any reply from the headquarters whether my appeal has been rejected or not. I want to participate in this contest but I can't unless this matter is resolved.

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    13 months ago, # ^ |
      Vote: I like it +173 Vote: I do not like it

    You cheated before. I have neither the time nor the desire to delve into the situation this time. You have exhausted your credit of confidence.

    For example, in Codeforces Round #700 (Div. 2):

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      13 months ago, # ^ |
      Rev. 2   Vote: I like it -32 Vote: I do not like it

      I have already accepted in my previous blog that I used two accounts for Codeforces Round #700 and I accepted all penalties for it without questioning. And as I promised in the blog, I stopped using my account Need_For_Sleep_MW. That round was the first and the last time I did something like that.

      I understand that it is hard for you and the community to believe me but all I want to convey to the community through this message is that I have never copied someone else's solution, nor provided anyone my solution during a contest.

      Thank you for the great platform and the community which helped me learn a lot of things and improve my skills. I hope I will not disturb you again.

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

I registered for the contest but I am unable to submit my code as it says that I have not been registered.

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

TOO LONG statements and quite bad experience on prob B

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

    What was the approach in Problem B?

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

      some kind of sorting + set (I did so)

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

      It is some case work.

      We want to buy the cheapest segment with min L, and the cheapest segment with max R. But we need to consider the extra case that one segment covers the whole range, ie has minL and maxR.

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

      Let $$$lx$$$ be the smallest $$$l$$$ and $$$rx$$$ be the biggest $$$r$$$ from $$$1$$$ to $$$i$$$. Then you have three options:

      1. Take segment $$$[lx, rx]$$$ if such exists (type 1).

      2. Take the cheapest segment that starts at $$$lx$$$ (type 2), take the cheapest segment that ends at $$$rx$$$ (type 3).

      Let's store the indices of the cheapest segments of types 2 and 3 in variables left_seg and right_seg respectively. When you find a segment with $$$l$$$ less than $$$lx$$$ or with $$$l = lx$$$ and less cost, reset the answer, update left_seg and of course $$$lx$$$ itself. Do the similar thing with $$$rx$$$. When you find a segment of type 1, try to improve the answer with its cost.

      Implementation (probably even clearer than my words above):

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

I hate English reading contest.

Back to IM.

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

long statement + very tough contest :(

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

After struggling for around 1 hour on problem D, I conclude that it is undoable for me ;_;

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13 months ago, # |
  Vote: I like it +95 Vote: I do not like it

After stopping for about two years, amiya participates in today's contest, Welcome back!

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

i dont agree with this blog

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13 months ago, # |
  Vote: I like it +17 Vote: I do not like it

Early congratulations to Gennady Korotkevich for the 1st to reach 3.9k! (hopefully...)

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

I'm sorry! This B let me goodbye 2022...

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13 months ago, # |
  Vote: I like it +22 Vote: I do not like it

Hello 2022(X

Hell 2022(O

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13 months ago, # |
Rev. 3   Vote: I like it -22 Vote: I do not like it

Sorry!

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

    I don't have any idea why you get WR in PreTest 1.

    but you code get WR in this case :

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

Problem B ate me

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

constraint in D so low why

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13 months ago, # |
  Vote: I like it +14 Vote: I do not like it

Problem B did me psychopath

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13 months ago, # |
  Vote: I like it +16 Vote: I do not like it

I usually never criticize contests, but

not-lighthearted meme
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13 months ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

I can't tell if D is either extremely standard DP problem or some extremely cute simple solution, can I get a hint?

Edit: Bruh I literally just realized that I forgot to account for half of the cases (extreme corners and the two top left corners of the (n/2)x(n/2) blocks not on the main diagonal. I'm so sad wtf ;-;

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

    Extremely cute simple :)

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

    I think the intended solution is DP based which is why constraint is so low (n<=250)

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13 months ago, # |
  Vote: I like it +36 Vote: I do not like it

I stuck in D for a long time ...

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

Where can I find the editorial for Hello 2022 Contest?

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13 months ago, # |
Rev. 2   Vote: I like it +15 Vote: I do not like it

B is an abomination. E is just boring implementation, too standard for its place.

F also seems like greedy casework. A, C are okay. D is nice.

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

I think the problem setters should focus on how to improve the skill of contestants of all levels. Not only differentiate winners and losers in a random way.

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

Only if I knew that the interactive problem would be pre-D prior to the contest.

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

Anyone else who thought problem C that, q initially identical as p, and waste a lot of time on it?

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

After this contest, I don't think I should have high hopes with 2022....

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

please explain the test case 4 in problem 4, I am still getting 44.

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

    The persons can also move out of the grid and enter on the opposite side.

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

    can you find a way to move such that at every stage every friend remains in one of below positions ?

    {a[i][j]: 1<=i,j<=n} U a[1][n+1] U {a[n+i][n+j]: 1<=i,j<=n}

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

How to solve C?

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

    In a permutation the numbers on the position form a circular list. The movement after each ask moves the number by one position within these circular lists. That means, by asking repeadetly one position we can get all numbers in that cirlce in the order they are in that circle. So resolve all circles.

    For me it was a implementation nightmare, did not get it right for like 1 and a half hours.

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    13 months ago, # ^ |
    Rev. 2   Vote: I like it +7 Vote: I do not like it
    Hint
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    13 months ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    Basically, we are given a kind of loop between which elements of the permutation q can rotate. e.g. if the original permutation was 4 3 5 6 2 7 1 ;we have the following rotation for q :

    In each step : q1->q4->q6->q7->q1 and q2->q3->q5->q2 .

    So, just keep iterating at any index whose value in the original permuation is not yet known and keep assigning the obtained value to the preceeding value/index till you reach the start of the loop again i.e. encounter a value twice. Then move to the next unknown index and repeat the process.

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

Is it just me , or problem B even is getting tougher these days

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

How to solve F?

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13 months ago, # |
  Vote: I like it +59 Vote: I do not like it

E was so boring.

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13 months ago, # |
  Vote: I like it +32 Vote: I do not like it

I hate Problem B (:

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

Are you serious? cyclic permutations + interactiveness for C! Meh Man!!

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

Imagine getting penalty (and time penalty because I doubted my solution) for D because of this: #define INF 999999999

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

Hi,pls help me to debug where I am doing wrong in the code : https://codeforces.com/contest/1621/submission/141566448

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

why this is wa? problem A- 141506189

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13 months ago, # |
  Vote: I like it +14 Vote: I do not like it

Happy Wrong answer on test case 2!!

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13 months ago, # |
  Vote: I like it +22 Vote: I do not like it

After giving this contest, I have a feeling that my 2022 won't be going well either.

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

im pretty curious why im getting WA for 2nd case problem B !

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13 months ago, # |
  Vote: I like it -128 Vote: I do not like it

The most terrible Problem B I've ever seen...

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    13 months ago, # ^ |
      Vote: I like it +104 Vote: I do not like it

    You are right. And I think Problem D which you only spent 3 min solving is much easier.

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      13 months ago, # ^ |
      Rev. 2   Vote: I like it -78 Vote: I do not like it

      Actually I've wrote a code for D at about 1:20 that I think it'll probably FST and, after solving E, I decided to submit it. That's why "3 minutes to solve D" exists.

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13 months ago, # |
  Vote: I like it +120 Vote: I do not like it

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13 months ago, # |
  Vote: I like it +108 Vote: I do not like it

Imagine how much better this contest could have been if F was just deleted

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13 months ago, # |
Rev. 3   Vote: I like it +161 Vote: I do not like it

In my opinion, this round was one of the worst in recent memory.

AB were not interesting, but it's hard to have interesting div2AB for a combined round, so I'll give them a pass.

In C, I'm sure there is a clean solution, but I immediately saw one solution, and had to spend a very long time making sure my indexing was correct. Also, in this problem it is hard to simulate the grader by hand, so I didn't even know if my solution would pass sample 1. I Think this problem would have been better if Q was always the identity permutation.

EDIT: turns out q at the start is always the identity permutation, and I just missed that part of the statement. As I stated above, my solution made no assumptions about what q initially is, which makes the problem much trickier to do. Please bold all important details in the future!

D is a one-observation problem. The observation is nice, but in my opinion this kind of problems shouldn't appear in a competitive programming contest. I most likely would never have been able to solve D if someone showed it to me and claimed it is very hard. Because so many people solved it, I just guessed random simple strategies until one worked. This kind of solving process is not fun.

In both E and F, you can immediately see a solution, but need to handle many cases to make sure your solution works on all inputs. Also, in both problems, the given sample is very weak, and covered less than half of the cases I had. I'm sure you have nice solutions to these problems, but if the optimal strategy to solve the problem is to just write tons of casework, it doesn't matter, it's a bad problem.

I did not get to problems after F, but at least from what I heard from others, G is not nice either.

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    13 months ago, # ^ |
      Vote: I like it +111 Vote: I do not like it

    I think D is very cool. I had full knowledge why the required algorithm is correct once the idea came to my mind (you need to move some corner at some point and any of these 8 cells suffices). I don't buy arguments "not suitable for a competition, because there is a cute observation constituting short solution", especially if it is not much harder to prove the correctness than to come up with the idea for the algorithm

    G is very cool as well

    But I agree with the criticism of ABCEF

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      13 months ago, # ^ |
        Vote: I like it +14 Vote: I do not like it

      I think D is boring too. That being said, I would have forgiven D in a contest where the other problems were better.

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

    I completely agree with your sentiment on D. I started off with an unproven solution (mainly because it was a D) before actually thinking about its correctness. While the idea is cute, I can totally see myself get stuck with it on another day and it would be extremely demoralizing in such scenario.

    I don't think E is bad though. It's a bit too standard and perhaps it's meant to compensate for D. Your approach is probably different from the intended one.

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13 months ago, # |
  Vote: I like it +128 Vote: I do not like it

First thank you to the author, I know it is a hard job preparing a full round.

Then, I would like to say that I did not enjoy the round. Partially because I am weak and I spent a huge amount of time on D (which I misread) and E (implementing) so I could not reach harder problems. But it is not only my fault:

  • In problem B it is obvious that at most $$$2$$$ intervals are necessary, then it is annoying to understand if $$$2$$$ or $$$1$$$ are necessary. And why are you asking for the answer on each prefix? It seems like it makes only the problem a bit worse.
  • Problem C contains no ideas, it is just a matter of knowing or not the cycle-decomposition of a permutation. A very boring interactive problem.
  • Problem E contains no ideas again. After reading it, I knew immediately how to solve it.
  • Problem F is screaming greedy. The first impression after reading it is "Ok, here we have to remove the short gaps as fast as possible and split in a gazillion cases". I did not get accepted (started implementing) in the contest and I have not read the editorial, so I might be very wrong, if that is the case I am sorry.

On the other hand, problem D was a nice tricky problem.

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    13 months ago, # ^ |
      Vote: I like it +62 Vote: I do not like it

    B and C is probably obvious to most red coders, but I think it's a great problem for their target audience. It is approchable, has some educational value, while requiring some thinking and implementation. And it is not "yet another math puzzle".

    D was a funny problem. I think the problem itself is not hard, but the limit being $$$250$$$ and the problem being in D made me feel nervous about my solution.

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

This really shouldn't have been the first contest of 2022 :(

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

F is such a terrible problem, stop creating problems like that.

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13 months ago, # |
  Vote: I like it -29 Vote: I do not like it

mathforces

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    13 months ago, # ^ |
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    man there was 1 math problem, and thats if youre liberal in the definition of math

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13 months ago, # |
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I guess in light of all the negatives everyone else mentioned, I thought problem G was a kind of cute DS problem, and my final implementation (that I just needed like 1 more min to debug in contest :sob:) ended up being relatively clean. A shame that it was buried in the back because CF logic seems to dictates that any problem with a range query is automatically harder than an ad hoc problem, no matter how difficult the ad hoc.

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13 months ago, # |
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At least the author hasn't formulated problem B on the grid

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

Didn't solve B because I was using $$$>$$$ instead of $$$\geq$$$.

Now I found out I FSTd on C because due to a basic out-of-bounds issue

sed life

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

Why is this contest so short? It is not some Anton round where every problem has a short solution.

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

+1054 delta when his rating is 3681 lol

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    13 months ago, # ^ |
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    inspect?

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      13 months ago, # ^ |
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      nope, you can check here. His seed was zero, because he has not competed in >= 6 months, but still interesting to see +1000 delta

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

        Oh, I use a carrot[extension] and it showed me -76.

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

No surprise in decreasing likes after contest (600->500). It was made for candidates and higher, not for ordinary folks, no Hello for them.

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13 months ago, # |
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Is this div1 or div2?

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13 months ago, # |
Rev. 2   Vote: I like it +428 Vote: I do not like it

Thanks for the contest, I enjoyed it!

A: fine easy problem.

B: I find it a bit interesting — even though it's just problem B — that it's possible to maintain the smallest $$$l_i$$$ and the largest $$$r_i$$$ on the prefix, along with the smallest costs of segments containing $$$l_{min}$$$, $$$r_{max}$$$, and both. Harder than an average B.

C: you can just find each cycle in $$$length + 1$$$ queries.

D: $$$8$$$ cells touch both $$$n \times n$$$ squares, and you need to clean at least one of them, otherwise you can't move friends from the corners of the original $$$n \times n$$$ square anywhere. At the same time, cleaning any of those $$$8$$$ cells is enough to move all friends to the destination. Definitely an interesting idea.

E: probably other solutions exist that use the structure of our queries. However, the somewhat standard idea "a matching exists $$$\iff$$$ for any $$$x$$$, $$$cnt_{teachers \ge x} - cnt_{groups \ge x} \ge 0$$$" along with a segment tree for range add and min does the trick.

F: basically just greedy simulation. There are four types of moves on $$$0$$$'s: replace $$$00$$$ with $$$0$$$ in an inner group, replace $$$00$$$ with $$$0$$$ in an outer group, remove $$$0$$$ from an inner group, remove $$$0$$$ from an outer group. The moves should be prioritized in this exact order, unless there are no $$$11$$$'s left, in which case you either replace any $$$00$$$ with $$$0$$$ and stop, or remove $$$0$$$ from an inner group and continue. It also follows that replacing $$$00$$$ with $$$0$$$ should always be done in the shortest group of $$$0$$$'s possible. Overall, this problem is fine. If your approach is more complex and you get stuck in the details, obviously you feel sad, but I believe my solution is reasonably simple.

G: a nice problem, did not seem approachable at first because it's hard to count increasing sequences containing two elements at the same time, but it turned out to be possible due to the structure of these pairs of elements.

H: looked hard initially, and I was pretty sure it would take a bunch of data structures to get through it. However, my final solution uses nothing except a single DFS, which is cool!

I: I think I can prove that after $$$O(\log n)$$$ iterations of $$$op()$$$ the array stops changing, but I could not figure out how to evaluate one $$$op()$$$ in $$$o(n^2)$$$.

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13 months ago, # |
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Can anyone explain me where my logic for the 2nd question went wrong?? I was stuck on it for almost the entire contest duration Link: https://codeforces.com/contest/1621/submission/141560841

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    13 months ago, # ^ |
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    The variable names are so similar even the compiler got confused, I guess.

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    13 months ago, # ^ |
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    Input
    Your Code Output
    Correct Output
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13 months ago, # |
Rev. 3   Vote: I like it +17 Vote: I do not like it

Seeing problem D in that place makes me immediately think of much more complicated approaches. I mean If I encountered this problem in div2-B I would've solved it in no time. This is a bad mentality I know.

But I do believe it's much easier than C, and after spending around 1 hour in C I did expect D to be much harder which was so annoying to see such a naive solution.

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13 months ago, # |
Rev. 2   Vote: I like it +15 Vote: I do not like it

For problem D,

0 0 0 5 5 5
0 0 0 5 5 5
0 0 0 5 5 5
5 0 5 1 1 1
5 0 0 1 1 1
5 5 5 1 1 1

Shouldn't the answer for this case be 9? From what I've seen the expected answer is 14

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    13 months ago, # ^ |
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    Try to rotate all your friends through your 9 cost path without stepping onto snowheaps. E.g. friends (3,1) and (3,3).

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    13 months ago, # ^ |
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    If you want to move only through zeros, you can move 2 columns from top-left to 2 consecutive rows in bottom-right. But you will not be able to move the $$$3^{rd}$$$ column. Remember that the whole column/row moves not only specific ones within it.

    EDIT: You will not even be able to move a $$$2^{nd}$$$ column from the top-left $$$n \times n$$$ square, as moving it will result in moving the $$$3^{rd}$$$ column to one of the columns with cost $$$5$$$'s.

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13 months ago, # |
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ProblemB,can anyone tell what might be the error. What i did is i maintain lowest integer and the minimum cost for such segment. And the highest integer and minimum cost for such segment. I also maintained fans variable which considers single segment case. If single segment not possible then sum of cost of lowest integer and highest integer will be the answer. Here is the code link. https://codeforces.com/contest/1621/submission/141533792

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    13 months ago, # ^ |
    Rev. 2   Vote: I like it +5 Vote: I do not like it

    Try this test:

    Test
    Your output
    Expected
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13 months ago, # |
Rev. 4   Vote: I like it 0 Vote: I do not like it

Will be very thankful if someone can explain my mistake in B — https://codeforces.com/contest/1621/submission/141579787 i commended the code, but i guess it's pretty easy, but still don't get what test doesn't pass and what's my mistake

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    13 months ago, # ^ |
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    Consider this test case:

    1
    3
    1 2 2
    3 4 2
    1 4 3
    
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13 months ago, # |
  Vote: I like it +106 Vote: I do not like it

A teacher/student with age $$$10^5$$$ in problem $$$E$$$:

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13 months ago, # |
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I don't think F is bad although it's all about the case work. (I'm saying this as someone who had a minor implementation bug when handling one last case and barely missed it)

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13 months ago, # |
Rev. 2   Vote: I like it +32 Vote: I do not like it

There are so many dubious accounts in this contest. iltt1, iltt2, ..., iltt7, ilg1, ilg2, ..., ilg6, ig1, igg2, ig3, ig4, ig5, ig6, ilt1, ..., ilt6, dk1, dkk2, dk3, dkk4, dk5, dkk6

These 31 accounts all submitted the same problems at roughly the same times with highly obfuscated code. They can be found in the 1100s in the standings.

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

Though I performed really bad, I feel EFG are really interesting. I agree with kpw29, recent rounds are becoming standard and boring, but this round gives me different feeling. Thank the author.

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    13 months ago, # ^ |
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    I never said that the rounds are becoming standard and boring ;__;

    Though I agree with happyguy656 — thanks for a good round!

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

Happy New Year!) And good luck on the next round!

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13 months ago, # |
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Happy new year! I hate this round!

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13 months ago, # |
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I think D is a really cool problem, one of the best in a while.

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13 months ago, # |
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Is anyone else wondering, what would happened if tourist reached 4000 contest rating ?

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13 months ago, # |
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Happy new year!

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13 months ago, # |
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Another contest for tourist to come first...lol

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10 months ago, # |
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Nice problems!!!