SlavicG's blog

Codeforces Round 964 (Div. 4)
By SlavicG, history, 5 months ago, In English

Hello Codeforces!

flamestorm, mesanu and I want to invite you to Codeforces Round 964 (Div. 4).

It starts on Aug/06/2024 17:35 (Moscow time).

The format of the event will be identical to Div. 3 rounds:

  • 5-8 tasks;
  • ICPC rules with a penalty of 10 minutes for an incorrect submission;
  • 12-hour phase of open hacks after the end of the round (hacks do not give additional points)
  • after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated
  • by default, only "trusted" participants are shown in the results table (but the rating will be recalculated for all with initial ratings less than 1400 or you are an unrated participant/newcomer).

Additionally, there might be problems that are interactive, so please read the guide of interactive problems before the contest.

We urge participants whose rating is 1400+ not to register new accounts for the purpose of narcissism but to take part unofficially. Please do not spoil the contest for the official participants.

Only trusted participants of the fourth division will be included in the official standings table. This is a forced measure for combating unsporting behaviour. To qualify as a trusted participant of the fourth 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 1400 or higher in the rating.

Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1400 (or you are a newcomer/unrated), then the round will be rated for you.

Many thanks to the testers: Dominater069, Qualified, Vladosiya, qwexd, Gheal, cry, haochenkang.

We suggest reading all of the problems and hope you will find them interesting!

Good Luck!

UPD: Editorial is out!

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

nice round

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

Let's see how many 1400+ rated coders will make a new account.

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

this will be a great round

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

as a tester, i didn't set anything

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

    hey, im new (2nd contest) so kindly help me out, i solved 4 out of 8 questions, my rating didnt increase yet. Does it take time or is there some other problem. My rating is 380 currently(less than 1400).

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      5 months ago, # ^ |
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      Hi, it usually takes about a day to update the rating.

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

      As it is explained in the announcement, after the round there is 12 hours long hacking phase, where participants can hack each other's solutions. After that, all solutions will be checked one more time, so rating changes will be visible in about 16-18 hours.

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

        it has been more than 24 hours now, still the rating has not reflected on my account yet. What about you guys?

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          4 months ago, # ^ |
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          After the contest there is 12 hours of hacking. After hacking there is system testing (currently been running for > 12 hours now).

          Seems like system testing should finish in the next 1-2 hours, after that they need to calculate rating updates. So rating should be updated in the next 12-24 hours.

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

why my current submissions are in queue for a long time any maintenance?

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

Participating unofficially :D Have fun yall

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

Yay! I always enjoy Div3 / Div4 round

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5 months ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it 
as a participant, good luck to you :)
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5 months ago, # |
  Vote: I like it 0 Vote: I do not like it

first time i participate in a round unofficially, good luck everyone

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

    I understand that feeling! :3 Good luck, m8! Don't listen to haters.

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

purpose of narcissism, lol

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

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

Hope to reach expert after this

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

I Hope to solve at least 4 problems in this contest, so that i can reach Pupil

I will come here after the contest

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

My first round, wooh hooh!!

Btw this is 1400 point round, so can I earn max of 4200 point in 3 games and surpass tourist ?! /j

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

    That's not how it works

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

      Whaat! Looks like my master plan failed before 1'st round..It's conspiracy against me I will tell you , XD

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    5 months ago, # ^ |
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    That’s not how it works man

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

    Seems like it won't be rated round for you... You need a history of 5 rated rounds already. Paradoxical, but that's how cf works. Compete in 5 div 2 rounds or smth, but first — good luck on this one!

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

      Read the bold line, it is rated for him. There is no sense in making contests (especially Div 4, meant for newbies) unrated becuase they have not participated in any rated contests xD

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

        Got it. That's actually good to know!!! Since I have friends that have 0 to 3 rated rounds in their history...

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

      It is rated for him, the point is that his performance in this round will not affect rating of the other Div. 4 contenders since he won't be on the official placement. This is made for smurfs in newreg accounts to not ruin fair Div.4 contenders' rating

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

Hope to reach 955 rating after this.

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

hope to reach 669 after this

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

hope to reach 700 rating after this. Whiss me luck

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5 months ago, # |
  Vote: I like it -7 Vote: I do not like it

GL everyone, hoping to reach Expert after next contest

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

    no you wont, I bet

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

      I feel like he will (look at his ratings)

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

        He'd need 202 points to make it to Expert :) (stop downvoting justnemat he's just made a mistake)

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    5 months ago, # ^ |
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    welp, not expert yet but close enough i guess

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

Thank you for everyone's effort to hold this contest. Let's go!!

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5 months ago, # |
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I will be playing Titled tuesday tomorrow, Sorry, I won't be able to participate this time. flamestorm mesanu

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5 months ago, # |
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Is there any DIv.5 on codefroces ?

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

My second contest... HUrrrrraayyyyyyyyy!!!!!

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

Good Luck Everyone! (Hoping to reach newbie after this)

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

is it rated?

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

    only rated for tourist

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

    if your rating is less than 1400 (or you are a newcomer/unrated), then the round will be rated for you.

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

Hope to reach pupil.

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

Hope to reach candidate grandmaster after this contest.

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

how many point i will get if solve all problem ?

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

hope to reach pupil in this contest!

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5 months ago, # |
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Good luck to us! I believe I will make >1200

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

big potato

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

Hope I don't need to leave codeforces after this contest.

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

I hope, this will be the last rated div4 for me

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

This will hopefully be my last rated Div4:)

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

As a tester, this round is very nice :)

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5 months ago, # |
  Vote: I like it +130 Vote: I do not like it

No greetings to MikeMirzayanov?

  • -1000 social credit

  • -1000 aura

  • -rep from Mike

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

I will solve all under an hour!

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

    i visited your profile.. you never solved all problems... speed is only your handle, lmao :)

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

interactive problems!!! we are cooked

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

Good luck to everyone

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

is it rated for me?

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

Interactive at Div.4? o.O

Is this the first time in Div.4 to have an interactive? If so, I would be really curious to see what it'd turn out.

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5 months ago, # |
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Hope it's my last div4

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

This is the first contest blog I have seen with no thanks to Mike.

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

if a 1400+ rated, participates with new account

then
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5 months ago, # |
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Hope to be Specialist after this contest.

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

hope to reach 1000 rating after this.

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

hope I can participating unofficially next div4 round

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

hope I will gain some rating through Div.4 contests which don't occur very often.

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

interactive problem for newbies and pupils. I think if newbies or pupils who can solve interactive problems, mostly the cheated or it's alt acc

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

    you want to say , in div 4 it only comes a binary search or two pointers and nothing more advanced , because it only rated for pupils and newbies?

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5 months ago, # |
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Good Luck and Have Fun!

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5 months ago, # |
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For the ones new to cpp and may not know much about interactive problems and flushing->

You dont have to flush the output when you are using "endl", just dont define endl as "/n" like many(including me do).

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5 months ago, # |
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Hope to reach pupil after this (to solve >= 5 problems)

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

after long time

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

easy round

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5 months ago, # |
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upvote if it's your first rated div 4

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

As a non-tester and non-participant, I would like to test future rounds (I never tested any round yet).

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

Let's go coders

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

As a pariticipant, LaLeii orz

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

As a participant, DangKhoizzzz orz

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

Da fuq, i think i cant solve all problem because of interactive problem, i hate this

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5 months ago, # |
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What the fuxk I already see a solution stream by an Indian on my YT main page.

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5 months ago, # |
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I really hope to become pupil or at least cross 1100 after this round. I am stuck between the 1000 — 1100 range for a very long time

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5 months ago, # |
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why is queue infinitely long

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

Queueforces

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

Queueforces

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

Inqueueforces

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5 months ago, # |
  Vote: I like it +53 Vote: I do not like it

Testing system is so overloaded that my solution exceeded compilation time: 274812981

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

Queueforces..

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5 months ago, # |
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Irritated with queue

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5 months ago, # |
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queue time is enough for me to playing a quick football games ;-;

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5 months ago, # |
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For ABCD, I spend much more time stuck in 502, 504, 405, etc. than solving problems

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5 months ago, # |
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Never make problem like B anymore...

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5 months ago, # |
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Why is cloudflare necessary (Genuinely asking)?

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

    To prevent DDOS Attack. But It defeats the purpose if it actually blocks/delays real user submission.

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

      Exactly :( each time i try to submit or refresh it takes longer time

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

My first ever AK!! Very nice problems :) especially G2

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

B>G1

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

I hate problem B

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5 months ago, # |
  Vote: I like it -19 Vote: I do not like it
hint for G
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5 months ago, # |
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Bro how to do B

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5 months ago, # |
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what is wrong here guys there is a run time error but I deleted my ncr and I used one from the internet and still run time error https://mirror.codeforces.com/contest/1999/submission/274946181

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    4 months ago, # ^ |
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    It could be that ncr should return zero if r is not within 0 and n inclusive.

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5 months ago, # |
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Div. 3/4 interactive = $$$O(logN)$$$ with binary or ternary search, classic

At least it can be easily stress tested, which is good

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5 months ago, # |
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solving till F. still rank in 4000's );

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5 months ago, # |
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easiest round imo where "hardest" task is low blue.

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5 months ago, # |
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got the formula for problem F, failed to solve the modulo thing... sadge

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5 months ago, # |
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how to solve B ??

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5 months ago, # |
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Why is Problem G two parts? Is there really a solution for G1 that will not pass for G2?

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

    binary search on a and always take b = 999

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

    I think that they probably intended Binary Search for Subtask 1 and Ternary Search for 2, since log2(1000-2) is about 10, while log3(1000-2) is about 6.

    But the ternary search solution would of course also pass for subtask 1.

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    5 months ago, # ^ |
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    yeah because log(999) is around 9 with base 2 which satisfies binary search condition for g1

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      5 months ago, # ^ |
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      I defaulted to binary search on G1, because I never had to implement ternary search(up until today w/G2).

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5 months ago, # |
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shitty round for python users

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    5 months ago, # ^ |
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    exactly... i need to switch to c++ soon

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    5 months ago, # ^ |
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    why though? I'm doing python just fine

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      5 months ago, # ^ |
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      the pypy compiler gave tle on the same solution where python3.8 worked fine

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

        I just checked out your D, and it's actually your fault that you got TLE.

        You keep appending to construct a long string (e.g. ans+=s[i]), which is slow. Python's string is immutable, which means it will always take $$$O(n)$$$ time to construct a string (where $$$n$$$ is the length of the string). Your code needs $$$O(n^2)$$$ time to run due to this, which is obviously not okay.

        It's interesting that Python runs faster on this code, though. I guess that it has some optimization (like skipping construction when there's only one reference). But whatever optimization Python has, you should avoid appending a string.

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          5 months ago, # ^ |
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          yeah,thanks a lot

          but what alternatives should i go for when i have a task like this?

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            5 months ago, # ^ |
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            String concatenation is a pretty basic technique -- try to google "build string in python" for in-depth tutorials. In sum, put string fragments into a list and do ''.join(list_of_fragments).

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

Can someone tell why this is throwing compilation error ?

same solution passes now

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    5 months ago, # ^ |
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    I got the same issue, the checker says: "Can't compile file: Compilation process timed out.", so I guess the server was just so overloaded that it can't even compile the file lol.

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5 months ago, # |
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I still don't understand how to solve B. I literally checked every possible case by hand. I don't know what's the right way to feel about this but I am furious.

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    5 months ago, # ^ |
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    Maybe u didn't consider when u win 1 round and tie the other (that happened to me)

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      5 months ago, # ^ |
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      No I did that, I did everything. I literally considered every possible way the numbers can be arranged relatively on a number line and this WA.

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        5 months ago, # ^ |
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        In your code in the if(bl==br) block, u ignore totally al, that part seems wrong to me.

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

          that part was a last ditch attempt at doing whatever to get AC, the code I actually wrote must be my second last WA submission for B.

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            5 months ago, # ^ |
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            btw the case when al == bl && ar > br that u insta print 2 is wrong, cause u can have br ==bl and that makes the answer to be 4

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              5 months ago, # ^ |
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              Hmm now I get it, I though about this problem of bl and br being equal at the last moment, and as you can see I did something about it in the last moment in my last WA submission for B. But maybe due to crunch of time I left some cases.

              Thanks I lot, now I feel good. I saw jiangly's solution anyway. To see what he did is to first observe that there is symmetry in the order of checking winning games. Say we flip a random card from Suneet and Slavic, then the other ones are fixed to be picked on the second round, moreover Those other two cards if picked first would produce the same final score. With this observation we can fix picking a1 first, then whatever I pick from b, I check whether my points are greater than the opponent. we do a1 with b1 and a1 with b2, get the result and multiply the answer with 2, because the case of a2 will conclude in symmetric final results.

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

              Also, changed the line you pointed out and it's working. 274963920

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    5 months ago, # ^ |
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    i used next_perumutation() function of c++, to brute force all possible combinations and check how many times player wins

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5 months ago, # |
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Why didn't authors announce the 10 mins extend earlier???

I was about to get E right, then I saw 30 seconds left and gave up. Later on I came back and saw the announcement that the round had been extended for 10 mins.

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5 months ago, # |
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Trolled in B and with the infinity queue took 40 min to fix the error xDn't

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5 months ago, # |
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How do you go on about solving F?

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    5 months ago, # ^ |
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    hint 1
    hint 2
    hint 3
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5 months ago, # |
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For D, I got WA on test case 1, but it worked just fine in my local compiler and online compilers

Lost multiple submissions, also each submission took too long to compile. Had to change same logic in python and it got accepted.

Couldn't find the reason, can you guys spot it? https://mirror.codeforces.com/contest/1999/submission/274845944

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    5 months ago, # ^ |
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    It looks like there's a small mistake on your for loop statement:

    for(int j = idx + 1; j < s.size(); j--) {

    The j-- should be changed to j++. Decreasing $$$j$$$ in the condition will result in an infinite loop or unexpected behavior since $$$j$$$ will never reach s.size(). Correcting this to j++ should resolve the issue and give you Accepted.

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5 months ago, # |
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Why this code is giving TLE in problem E.1999E - Triple Operations

Spoiler
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    5 months ago, # ^ |
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    there is no restriction on l and r. So your code could iterate for 2e5 times for each testcase if all testcases have l=1 and r=2e5.

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      5 months ago, # ^ |
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      Is this really the reason? I have a similar submission that passes but loops through l -> r:

      274871369

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        5 months ago, # ^ |
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        You are correct. I tried to hack your solution but looks like your solution is could also have been tle had you used unnecessary local variables inside loop, instead of directly reading values from SOL array like you are doing now.

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    5 months ago, # ^ |
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    You are looping from a to b for every test case. Imagine if there is 10000 test cases, each has a=1 and b=200000. Then you will TLE.

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    5 months ago, # ^ |
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    there is no limit over the sum of l or r over all tests. Therefore, iterating from l to r is not viable for big number of tests. Try with prefixsum

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    5 months ago, # ^ |
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    If you iterate in a to b, it would go upto 10^4*10^5 iterations in total. Raising TLE. There was no limit like sum of iterations being less than 2*10^5

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5 months ago, # |
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Can I ask a question here?

In problem E, my code was giving me expected/correct output in my local machine, but is giving wrong output during codeforce's testing 274941437

Could any one tell why is that?

Btw, it was a great first experience to my first cp round :)

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

mathforces

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5 months ago, # |
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Can someone explain how this is TLE:

https://mirror.codeforces.com/contest/1999/submission/274946145

let n be 2*10^5, where l and r are <=n

the while loop is log3n and the for loop is constant operations in O(N) time as well

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    5 months ago, # ^ |
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    You are looping from l to r for every test case. Imagine if there is 10000 test cases, each has a=1 and b=200000. Then you will TLE.

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    5 months ago, # ^ |
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    ur complexity is t*n_max, which will give TLE

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    5 months ago, # ^ |
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    Your time complexity is not NlogN. It's T*NlogN. Usually, you don't worry about it because it's stated N won't exceed 1e5 across all T for example, an important statement missing from this problem

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    5 months ago, # ^ |
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    But, 1≤t≤10^4 and 1≤l<r≤2⋅10^5. You iterate over [l, r] in every t. So it's n^2

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5 months ago, # |
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Tanked 5 TLEs on E because I calculated the prefix array in the solve() function :( Also couldn't figure out why I got WA for G2 test 2

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5 months ago, # |
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How did so many people solved D?

E was just algebra and prefix sums

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    5 months ago, # ^ |
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    I solved E greedy no algebra involved

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      5 months ago, # ^ |
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      yeah just precompute the logs, that's what tricked me to tle

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    5 months ago, # ^ |
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    D is completely based on a pretty common idea, that finding string as a substring in another string is successful iff it's successful greedily.

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5 months ago, # |
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Hmm, quite easy div4, compare to the last 2 recent div4 rounds.

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    5 months ago, # ^ |
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    DuongForeverAlone orz. I've failed problem F since I don't know how to handle the modulo formula stuff. Else it's gonna be a blast for sure compared to recent div4 rounds

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      5 months ago, # ^ |
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      i used modular inverse and binominal coeff formula

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        5 months ago, # ^ |
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        Hi can you tell me what is wrong with my code in problem F it's run time error at first I wrote my own ncr and fast power but after stuck with the run time eror I copied one from the internet but still run time error there is a big mistake but I can't see it https://mirror.codeforces.com/contest/1999/submission/274946181 it would have been my first time to solve till F

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          5 months ago, # ^ |
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          You missed the new line after printing LOL.

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            5 months ago, # ^ |
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            still there is run time error the last case is giving different answer every time I compile it

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          5 months ago, # ^ |
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          ll fact[200003];
          i<200009
          also you are not printing new line in each test case

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            5 months ago, # ^ |
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            I just fixed them and got WA on test 3

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              5 months ago, # ^ |
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              what if K > N you didn't handle that

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                5 months ago, # ^ |
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                yeah thanks that was the problem

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      5 months ago, # ^ |
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      For modular issue (especially modular inverse), it has been one year since I implemented those things last time. After using the Modular class (actually I copy from tourist, but with some modifications), I could handle those modular operations with ease. I recommend to take a look at it.

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        5 months ago, # ^ |
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        sure, I think I will also copy python class from better players in the contest. Have to take the hit for the experience tho. (But not sure if this will be marked as plagiarism)

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    5 months ago, # ^ |
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    especially Div4G. But it does serve as a good intro to interactives.

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5 months ago, # |
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B is the hardest easiest problem.

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5 months ago, # |
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B is the hardest easiest problem

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5 months ago, # |
← Rev. 2   Vote: I like it +16 Vote: I do not like it

Best of luck everyone

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5 months ago, # |
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The waiting queue is fucking long

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5 months ago, # |
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In problem B, why don't we count the game starting with Suneet and Slavic separately?

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5 months ago, # |
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it sames like every one can solve problem F, it's really hard for me

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5 months ago, # |
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Any specific reason behind these very long wait queues in div3/4 contests? In my case today one submission took >15 minutes to resolve?

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5 months ago, # |
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Just got an observation for E:
[1, 3) -> all elements require 1 operations to become 0
[3, 9) -> all elements require 2 operations to become 0
[9, 27) -> all elements require 3 operations to become 0
[27, 81) -> all elements require 4 operations to become 0
[81, 81 * 3) -> all elements require 5 operations to become 0
and so on.

I think this could be optimal.

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    5 months ago, # ^ |
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    Yes u can see my solution I solve it using this observation

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5 months ago, # |
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My wifi was cut off 40 mins after contest started. After that I tried whole time to enter the contest, I was getting verified but they were not entering me in the contest..

Now what? I will loss around 40 points for what? Inconvenience by Codeforces website?

Yes I tried the m2codeforces website too.

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5 months ago, # |
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Enjoyed the round. Great problems. Couldnt solve F (cuz im bad with mathy type problems). +100 Delta letsgoo

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5 months ago, # |
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for those who think that div — 4 is too easy for them. 1. find the 1000 consecutive integer where non of them are prime. 2. find the 1000 consecutive integer where exactly 10 of them are prime ENJOY.

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5 months ago, # |
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Please explain why this doesn't work in problem B (says expected 4, found 0 on 101st test case): https://mirror.codeforces.com/contest/1999/submission/274897075

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5 months ago, # |
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can anyone explain the tle 274928746 for each testcase t it takes at most 10^5 iterations times log(10^5)base3

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    5 months ago, # ^ |
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    It will fail for the cases when one of the rounds are drawn. For eg.

    1 10 2 3 2

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5 months ago, # |
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Why does this give tle in test case 1 of E Submission

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5 months ago, # |
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why i got wa in 2nd test case.. 101st "wrong answer 101st numbers differ — expected: '4', found: '2'"

here's my solution: My B solution

can anyone explain, please???

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    5 months ago, # ^ |
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    mayb its because you are not considering the a==c and b==d and a==d and b==c etc. these cases

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      5 months ago, # ^ |
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      in these cases Suneet loses the round , right? but only considers those cases in which suneet wins i.e; (a>c && b>d),(a>d && b>c),(b>d && a>c),(b>c && a>d)

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        5 months ago, # ^ |
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        if it is a tie then it is not losing for suneet .. if he wins the other round he still wins the game ( it's in the problem statement but yeah this problem sucks :) )

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5 months ago, # |
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Thank you guys for the great contest!

Couldn't figure out the scenario of 1 win with 1 draw in problem B and the precision error when use log Math function in problem E, but glad that I've up-solved them just now.

After all I still enjoyed the contest!

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5 months ago, # |
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interactive problems are SHIT

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5 months ago, # |
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Struggled solving F for over an hour with multiple submissions failing at testcase 16+ because of mod (made me sad especially after I seeing that G was just ternary search :( Otherways very nice contest

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5 months ago, # |
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on paper this gives best answer but why it fails on test cases ? `** ** ~~~~~ int fun(ll x){ int count = 0; while(x){ count++; x = x/3; } return count; } `** **void solve() {** ** ll l, r;** ** cin >> l >> r;** ** ll ans = 0;** ** ans += fun(3*l);** ** for(int i = l+1; i <= r; i++){** ** ans += fun(i);** ** }** ** cout << ans << endl;** **}```` ~~~~~

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    5 months ago, # ^ |
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    Actually it should be ans+=2*fun(l) instead of ans+=fun(3*l) and also you got to precalculate those values using prefix array or else you will get tle ig

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    5 months ago, # ^ |
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    The only problem with the logic is when you increas ans by fun(3*l) instead of 2 * fun(l). For example if l = 9 we would want to reduce the 9 to 0 first. To do that we would have fun(9) = 3 operations but simultaneously another number would be multiplied by 3 two times. And to reduce it to its original value we would again need fun(9) = 3 operations. That's why ans has to be 2 * fun(l).

    Also your code will hit TLE since you always recalculate fun(x). Instead of that you could precompute all of the needed values. I did it like this:

    vector<int> steps(200002);
for(int i = 1; i < 200001) {
    steps[i] = steps[i / 3] + 1;
}
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5 months ago, # |
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sooooo bad contest

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5 months ago, # |
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submission 1 submission 2 CAN ANYONE PLEASE EXPLAIN WHY BOTH OF MY THIS SOLN GIVE WRONG ANS ON TEST 2 TODAYS DIV 4 B

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5 months ago, # |
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how this solution have passed flamestorm

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    5 months ago, # ^ |
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    Exactly, my same code gives TLE

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5 months ago, # |
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Can someone please tell me why my code for D failed? code: 274969671 I got this error: wrong answer Token parameter [name=ans_string] equals to "hjcjcng~", doesn't correspond to pattern "[a-z]{8}" (test case 163)

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    5 months ago, # ^ |
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    You need to replace all '?' With any other alphabet in [a-z]. Because as stated in the question- Slavic is asked to change each "?" to a lowercase English letter

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5 months ago, # |
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I am getting Idleness limit exceeded, How can this be fixed?

274961116

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    5 months ago, # ^ |
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    ? a b — in response, we will measure the side lengths of an (a * b) rectangle

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    5 months ago, # ^ |
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    I think you implemented the binary search wrong, so that it doesn't halt. instead of setting l/r to x you need to set it to l+1 or r-1 and also instead of checking wether r-l > 1, you need to check wether l is smaller or equal to r.

    Let me know if this works!

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    5 months ago, # ^ |
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    Remove this line #define endl "\n"

    Ah no, actually your query is wrong, you need to cout 2 values

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5 months ago, # |
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lowkey B is the hardest problem here.

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5 months ago, # |
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How some brute force solutions passes in problem E ?

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5 months ago, # |
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Was a good round!

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5 months ago, # |
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can you remove any codes using AI ? I know an account the code awritten using ai and this not fair!!

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5 months ago, # |
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Good round, hopefully I can be a specialist.

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5 months ago, # |
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Wow

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5 months ago, # |
  Vote: I like it +19 Vote: I do not like it

Just virtual'd this contest, nice query limit at G2! It's so strict that even a minor suboptimal tactic resulted in a wrong answer, and for educational purposes I really endorsed it!

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5 months ago, # |
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div5??hhhh

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5 months ago, # |
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I haven't participated since the last year, and I was hoping to got this round rated... :( Isn't there any way to have this as a rated one. At the morning I was a contestant and now it seems to be a practice round. I don't know how many points do I deserve

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    5 months ago, # ^ |
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    System testing is running,in a few hours rating will be updated

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    5 months ago, # ^ |
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    well, system testing is taking forever and probably won't be done for a few more hours. So ratings probably updated tomorrow

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5 months ago, # |
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G1 and G2 were quite interesting learned about Ternary search.

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5 months ago, # |
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Waited 27mins in queue for G1 just to get compile error :)

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5 months ago, # |
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Is there an additional penalty if I hack someone else's code multiple times and it doesn't work?

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5 months ago, # |
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Hi Everyone

For Problem E ( E. Triple Operations) , I precomputed all the values using log_base_3 , but somehow it's giving incorrect result for 243 and 59049 , to pass the test cases i had to hard code the result , can anyone please help me here , why it's giving incorrect result.

For log values calculation i realized that precision values depend on the gcc compiler weird

Here is my submission — https://mirror.codeforces.com/contest/1999/submission/274923066

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    5 months ago, # ^ |
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    Check this and this comment.

    As far as we're concerned, we only care about the integer floor of the log, and the numbers to get logarithm from isn't too huge, so we could actually bruteforce the log3 by continuously dividing the number by 3 until it reaches 0. TL;DR try to avoid floating point arithmetic as much as possible to escape precision issues.

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      5 months ago, # ^ |
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      I use continuously dividing method and get TLE

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        5 months ago, # ^ |
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        Precalculate your logs and call them when needed.

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5 months ago, # |
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It was one of the best round I ever seen. Thank you !

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5 months ago, # |
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Its been 16 hours from start of the contest now, does anyone know when system testing starts and when rating update will happen ?

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    5 months ago, # ^ |
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    hacking phase of 12 hrs was going on but ig its done now so we'll be updated in 2-3 hrs!

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5 months ago, # |
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my can someone help me this 275053244

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    5 months ago, # ^ |
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    The issue is with the way you are making the final string (the usage of ind). Use this test case,

    1
ab?d?
abcde

    Your code will give incorrect solution to this. Try to see why.

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    5 months ago, # ^ |
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    1
    abc?ef?h
    abcdefgh

    Try this.

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5 months ago, # |
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Help!!! All of my race records have disappeared!!!! WHY!???

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5 months ago, # |
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This might be the longest system testing ever,will go on for more than 10+ hrs.

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5 months ago, # |
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good contest:)

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5 months ago, # |
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queueforces

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5 months ago, # |
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bruh system testing is

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4 months ago, # |
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How much longer do we need to wait for ratings update? And how do y'all get to know when system testings are going on?

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    4 months ago, # ^ |
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    go to the main contest page, where the problems are listed and on the right it will show the system testing progress.

    looks like it will take another 1-2 hours, ratings will probably take 12-24 hours after that.

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4 months ago, # |
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System testing is taking forever. Waiting for results for 12hrs.

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    4 months ago, # ^ |
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    Yeah fr! I like codechef's live rating. It would be great if something like that was introduced here(Ik we got open hacks, recalculation and all, but what i am suggesting is provisional rating which could fluctuate...)

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      4 months ago, # ^ |
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      you can use carrot extension :)

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        4 months ago, # ^ |
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        it's not accurate

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        4 months ago, # ^ |
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        Whats this? I am new in codeforces so i would appreciate if you could help me!

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          4 months ago, # ^ |
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          it is an extension which predicts your rating change before actual change in rating. It gives you rough idea about how much your rating will change.

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4 months ago, # |
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I have one question ?

Are all Interactive Problems are Solved By Binary Search or Ternary Search

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4 months ago, # |
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Is it just me who think B>>>>>>>>>>>>>>> C+D

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    4 months ago, # ^ |
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    B was a straightforward question(I got it wrong two times due to overthinking?). It was just written in such a way that it was treated as a much more complex qs than it actually was lol.

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4 months ago, # |
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where my contest rating updates at?

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4 months ago, # |
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Nice round! I've become Specialist after this contest!

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4 months ago, # |
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Hope this difficulty can like rated Div.4 and i can get 1000

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4 months ago, # |
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MikeMirzayanov I have been found guilty of solution coincidence. Here goes the detail :

"Your solution 274369201 for the problem 1993B significantly coincides with solutions Varun_171/274369201, maneesh5164/274406896. Such a coincidence is a clear rules violation." But I haven't cheated nor involved in promoting cheating and my submission time is well before the other guy's submission.

Kindly consider the chances of coincidence, this is the first time I am getting this kind of warning. Maybe i chose very trivial variables, but I don't have idea about this high coincidence.

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4 months ago, # |
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Can anyone please explain for me why does my solution to problem E had TLE thnx a lot 274877212

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4 months ago, # |
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The appearance of this blog is to appeal the CF official sentence for my 1999F code。

Attention!

Your solution 274818573 for the problem 1999F significantly coincides with solutions daoqi/274818573, Haz_Begonia/274828630. Such a coincidence is a clear rules violation. Note that unintentional leakage is also a violation. For example, do not use ideone.com with the default settings (public access to your code). If you have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, write a comment to post about the round with all the details. More information can be found at http://mirror.codeforces.com/blog/entry/8790. Such violation of the rules may be the reason for blocking your account or other penalties. In case of repeated violations, your account may be blocked.

【Codeforces Round 964 (Div. 4)AK实录】https://www.bilibili.com/video/BV17iameiEN8?vd_source=958d8670804c24a04935dc3755fc300a

Because I happened to be recording this game, you can see that the code for my F was written by myself。

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4 months ago, # |
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Appeal against the incorrect skipped verdict of my Problem D submission

Greetings!

I want to appeal against the cheating verdict received for my submission of problem D of this round. I received the skipped verdict for this submission. I haven't copied this code from any public source, and I have completely written it. The logic for this code is pretty simple greedy approach and I believe that's the reason of the coincidental match with others solutions. I promise you to take a look at the rest of my submissions for this contest, combined with the submission. linked above will prove my innocence. Below are a few submissions, with whom my submission is claimed to coincide: anekdot/274758762, DevNorms/274768558, kvasilek/274772612, el_lobia/274776109, krizsu/274779701, long_off_long_off_sky/274781618, romtec/274784433, drgrenkenstein/274785579, Sino_2009/274792605, neheka9385/274792761, .Miraitowa./274794390,

MikeMirzayanov

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4 months ago, # |
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I am writing to bring to your attention an issue I have encountered regarding similar code submissions on this Div.

Recently, I have noticed that my submission for the problems , closely resembles other submissions made by different users. I believe this similarity is coincidental, as I wrote the code independently and have no intention of violating the platform's guidelines. some of people write with another language how code be the same ?

I kindly request that you review the submissions in question to ensure there is no misunderstanding and that my submission is evaluated fairly.

MikeMirZayanov

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4 months ago, # |
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I received message from codeforces that my solutions for problem E matches with solutions of some other contestants. I did not used any unfair means. Also, I am pretty sure there was no leakage of code. The similarity may be found because main thing in the question is logic & the code is short (only 10-15 lines) and the variables I used are common. So, the similarity is purely coincidental. This is the first time I received such a message. Please look into this matter.

Thank you.

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4 months ago, # |
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Hi MikeMirzayanov I am writing to address the recent notification regarding the significant similarity between my submission:274919032 for Problem 1999E - Triple Operations and the solutions of other participants. My solution use a piece of my pre-written Prefix sum which is stored publicly here. As you can see, my other earlier TLE submission is about by not using this prefix sums trick. Thank you for your attention to this matter. I hope for a fair resolution. Thanks

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4 months ago, # |
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Posting this, because I received a message from codeforces saying that my solution (274849687) for the problem 1999D significantly coincides with some other solutions. Just to clarify, I did not use any unfair means in solving this question or any other question in any of the past contests. And I do not intend to do so in any future contests either. I am confident that there was no leakage of code because I have done it entirely in my computer's editor and submitted it to Codeforces directly. The logic to this question was pretty simple, and coding the logic takes only 10 lines. So there is definitely a high chance that many contestants will have similar codes purely due to coincidence and not due to any sort of malpractice. You may check the timings and my other codes to convince yourself of my innocence.

Kindly look into the matter and do not penalize me for any mistake of which I am not guilty. This is my first time receiving such kind of message, so please message me if there is any need for any detail.

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4 months ago, # |
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Appeal for False Accusation of Code Plagiarism Hi MikeMirzayanov, I hope you're well. I’m writing to bring to your attention that I’ve been falsely accused of copying the solution for problem 1999D 274836235. I assure you that my solution was developed independently, and I take the rules of fair competition very seriously. Could you please review my case? I’m happy to provide any additional information that might help clarify the situation. Thank you for your understanding.

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4 months ago, # |
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MikeMirzayanov This comment is an appeal against the plagiarism verdict on my 274805223 for problem 1999D - Slavic's Exam.

I want to make it clear that I wrote the code entirely by myself and didn’t copy it from anywhere or use any external code.

The solution code is pretty short—only 10-15 lines (in the solve fucntion)—and the logic is straightforward. I used some trivial/common variable names, which might explain the similarity with other submissions. But honestly, it’s just a coincidence.

Please take a look at my other submissions in this contest too. 274850363, 274783573, 274754028, 274713747. I think you’ll see a consistent approach and the same use of debug template in all of the submissions. Even in this particular submission I have used multiple debug statements in the solution which proves my innocence. If I had copied the code, there was no need for me to go through the debug process while solving the problem, this shows my code is original.

This is the first time I’ve had this issue, and I’m confident it’s just a misunderstanding. I appreciate you looking into it.

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4 months ago, # |
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.

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4 months ago, # |
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MikeMirzayanov I have been found guilty of solution coincidence. Here goes the detail :

hi, today i got a mess that i have cheated in (solution 274934350 for the problem 1999E) but i want clarify myself i havent done any cheating and the solution thats showing are matching aren't matching mine and there solutions are different i have also used some extra functions which you can see and also dont need to cheat in div 4 contest cause its unrated for me so why would i cheat but yeah i have done a small mistake that i have got some error issues in hidden testcase so i have given the code to chat gpt to solve the error,i think thats why its coinciding with some solutions ,so plzz remove the message from my profile as its not a good remark for my profile

Kindly consider the chances of coincidence, this is the first time I am getting this kind of warning. chat gpt has changed my variables by there own, but I don't have idea about this high coincidence.

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4 months ago, # |
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Hey!

I got plaged in this round at problem D. I don't know how. I use to give Claude AI my codes to rewrite it and make it not readable but keep the logic same. I use to do this after my solution was hacked by someone a while ago. My friend suggested to make the code less readable. But I can't be plaged for that. Since the code for this problem was very short it matched with some other guy. But please look closely at this code.

MY UPLOADED CODE is (that was rewritten by claude) — this

MY ORIGINAL CODE is — this

I was asked to post comment here to help me with my plag. Can someone please help me with this?

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    4 months ago, # ^ |
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    .

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    I was also got plaged with him I used Claude ai for solving that problem. You can simply try to give whole question as a prompt and you will find the same solution.As Claude ai code was available before the contest I should not got any plag.

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4 months ago, # |
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I am writing this comment to appeal for a wrongful accusation of cheating on me. I got an email last night that my solution 274819760 for 1999D - Slavic's Exam matches many other users'(whom I don't even know).

I assure you that all of my code was written in VS Code. I don't use any online compilers. This is the first time I'm getting this type of warning. I suppose my solution got flagged because of replacing the '?' with any lowercase letter, most people will first think of 'a' or 'z'. Also, the logic of this code is pretty trivial and straightforward, so there is a high chance that many other contestants used similar logic. The similarities are purely coincidental. The other submissions that I was accused of copying from were also not very similar to my code. I also wrote a redundant recursion function and a bunch of other redundant lines of code which were not needed that I forgot to remove while I was looking for an approach to solve the problem and debugging which proves my innocence.

I request you to look into my case and do not penalize me for any mistake of which I am not guilty of. I’m happy to provide any additional information that might help clarify the situation. Thank you for your understanding.

Here's the mail which I got:

Message
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4 months ago, # |
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Hi everyone,

I'm reaching out because I’ve been wrongly accused of plagiarism for solution E. I want to clarify that I have neither shared my code with anyone nor copied it from anyone else.

You can verify that my previous submission resulted in a Time Limit Exceeded (TLE) error, and I’ve since optimized my approach by memoizing all possible results in a vector. I’m more than willing to answer any questions or provide further explanations regarding my solution. This might be a coincidence.

I would greatly appreciate your assistance in resolving this matter.

Thank you.

MikeMirzayanov SlavicG

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4 months ago, # |
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Hello everyone, I received a notification saying one of my solutions(C) matches with another user. i do not think my code was leaked during the contest, nor i shared it afterwards, I worked on it all on my own. this might be a coincidence. I can assure i started the contest a little late, but i worked on it on my own, i was really looking forward to a div 4 contest. I am still confused how my code can exactly match someone elses, i usually use vs code or codeblocks for compiler, never used an online compiler, i feel like there's been a mistake, and not sure where else i can go for review.

I would appreciate if someone can help me in resolving this matter.

Thank you. MikeMirzayanov SlavicG flamestorm

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    4 months ago, # ^ |
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    Did you get any reply?

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      4 months ago, # ^ |
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      not yet, i already gave up, my rank went so high after that contest they removed that too, not my fault div4 has too many people joining that it keeps getting overloaded

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4 months ago, # |
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Attention!

Your solution 274827714 for the problem 1999C significantly coincides with solutions mh_sakal/274827714, red-code/274915868. Such a coincidence is a clear rules violation. Note that unintentional leakage is also a violation. For example, do not use ideone.com with the default settings (public access to your code). If you have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, write a comment to post about the round with all the details. More information can be found at http://mirror.codeforces.com/blog/entry/8790. Such violation of the rules may be the reason for blocking your account or other penalties. In case of repeated violations, your account may be blocked. this message is showing on my id .but both accounts are mine. I have two codeforces account and I used same code for the both account. So what can I do now?

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4 months ago, # |
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MikeMirzayanov This comment is an appeal against the plagiarism verdict on my 274779515 for problem 1999D — Slavic's Exam.

I want to make it clear that I wrote the code entirely by myself and didn’t copy it from anywhere or use any external code.

The solution code is pretty short—only 10-15 lines and the logic is straightforward. I used some trivial/common variable names, which might explain the similarity with the other submission.

As you can see the contest was unrated for me along with the user whose submission has been flagged with mine 274762618, which clearly shows that neither of us had any reasons to copy the code, also I have noticed that many people have written a similar code which shows that the solution to this question was pretty trivial.

This is the first time I’ve had this issue, and I’m confident it’s just a misunderstanding. I appreciate you looking into it.

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