mesanu's blog

Codeforces Round #784 (Div. 4)
By mesanu, 3 years ago, In English

Hello Codeforces!

SlavicG, flamestorm, MikeMirzayanov, Errichto, and I want to invite you to the long-awaited second Div. 4 round!

It starts on Apr/21/2022 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).

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 behavior. 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: senjougaharin, magnus.hegdahl, Vladosiya, MeGustaElArroz23, Sho, bakekaga, geranazavr555, doreshnikov, jampm, Neophiliatic, qwexd and VIP-tester _Vanilla_.

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

Good Luck!

Update: Editorial

  • Vote: I like it
  • +432
  • Vote: I do not like it

Comments Comments (149)
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3 years ago, # |
  Vote: I like it -91 Vote: I do not like it

As a tester, https://discord.gg/mPACFtYvwF

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    3 years ago, # ^ |
      Vote: I like it +26 Vote: I do not like it

    Thanks to MikeMirzayanov for polygon platform.

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    3 years ago, # ^ |
      Vote: I like it -26 Vote: I do not like it

    Can we please get back to programming?

    I truly don't mean for this to come off as insincere, insensitive, or trying to diminish the importance of these events to people's personal lives.

    But that being said...

    Codeforces isn't the place for such debates. I'm not saying these discussions don't need to happen. They do. But them happening on this surface is essentially well-intentioned spam.

    This stuff belongs on social media, or places like Reddit and Discord.

    Alright, I've spoken my peace, bring on the flood of downvotes...

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3 years ago, # |
  Vote: I like it +7 Vote: I do not like it

As a participant (hopefully), thank you for the round!

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3 years ago, # |
  Vote: I like it +2 Vote: I do not like it

I was not expect this combination of authors. Will definitely be doing the contest.

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3 years ago, # |
  Vote: I like it +15 Vote: I do not like it

Hope I turn Pupil this round

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3 years ago, # |
  Vote: I like it +50 Vote: I do not like it

As a VIP-tester, I tested

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    3 years ago, # ^ |
      Vote: I like it +18 Vote: I do not like it

    Oh, that must be nice...

    But can somebody tell me?!
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3 years ago, # |
  Vote: I like it -66 Vote: I do not like it

as a potential participant, 接受我 公众 我需要现金

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    i can‘t understand

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

    As a Chinese and not understanding.

    maybe 接受 means accepted.

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

jampm the best tester Upd: the second best tester

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    3 years ago, # ^ |
    ← Rev. 2   Vote: I like it +4 Vote: I do not like it

    Sorry but I do not see his VIP status, opinion rejected.

    UPD: They realised I am the best tester.

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

    i cannot believe how CF got jampm for tester, he is known as a God. Very humble participating as tester.

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

From now, can we expect div-4 frequently ?

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3 years ago, # |
  Vote: I like it +201 Vote: I do not like it

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

I can't wait to see problem ratings lol

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

problem D will be very interesting i swear

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

As a participant, I hope to be unofficial to div4s after this contest.

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

What about score distribution ?

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    3 years ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    Div 3/4 and Educational rounds doesn't have score distribution.

    Its just number of problems solved + penalty

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3 years ago, # |
  Vote: I like it +55 Vote: I do not like it

"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."
I respect that a lot.

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3 years ago, # |
  Vote: I like it +60 Vote: I do not like it
:)
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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

As a participant, since when do div 4 contests exist lol.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

looking forward to 1900 rated F,G. (Totally not an analogy to 2000-2200 rated F,G problems in Div. 3 rounds, but they are sure very interesting for Div. 3 users when none of them can solve the problems xd)

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

My first Div.4 round. This is going to be interesting Thanks for the round!

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3 years ago, # |
  Vote: I like it +48 Vote: I do not like it

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

looks like I got back to pupil from specialist just to participate in this contest officially xD

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

After a long time finally there is a (Div.4). (REALLY EXCITED) ٩ (◕‿◕｡) ۶

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

Specialists be like : Yo maann! Outta competition.(⌐■_■)

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Just realized out of 10 Level of Colors

Spoiler
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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

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3 years ago, # |
  Vote: I like it +12 Vote: I do not like it

Errichto it is a pleasure to see u after a long time .

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3 years ago, # |
  Vote: I like it +18 Vote: I do not like it

What a great time to be rated 1399

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3 years ago, # |
  Vote: I like it -40 Vote: I do not like it

This contest is just a joke, low rating participants should go to leetcode first.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Anyone have link for the codeforces extension for the graph and all of this.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

HAHA, I looked forward to my first unrated round, and it was supposed to be after a long time. But the Div.4 round comes. Thanks!!!

This will be my first unrated round. Good luck everyone!

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3 years ago, # |
  Vote: I like it +2 Vote: I do not like it

Good luck to all my fellow newbies and pupil. It's their time to shine. All the best :)

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Can anyone give me the previous(1st) Div-4 round link, plz?

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

Hooray, round for my level)

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

my first unrated round

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I hope that I'll learn something and get better in a unrated round so that I can earn rates in a rated round.

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

Thanks to MikeMirzayanov for polygon platform and CodeForces team!

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

Feels weird to say MY FIRST UNRATED ROUND!!

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3 years ago, # |
  Vote: I like it +4 Vote: I do not like it

First unrated round for me)

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it
Those who know, knows.
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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Is it rated?

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

FastFingersForces

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3 years ago, # |
  Vote: I like it +22 Vote: I do not like it

Previous div4 was probably harder than this

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3 years ago, # |
  Vote: I like it +11 Vote: I do not like it

fanserviceforces

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3 years ago, # |
  Vote: I like it +31 Vote: I do not like it

D is the hardest

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3 years ago, # |
  Vote: I like it +4 Vote: I do not like it

The easiest contest ever proposed in the history of universe.

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3 years ago, # |
  Vote: I like it +2 Vote: I do not like it

I went rainboy mode in this contest.

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

There are many accounts that was made just yesterday and they are in the top 100 lol

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

Great round for 4th division!

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3 years ago, # |
  Vote: I like it +45 Vote: I do not like it

Me in this contest

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3 years ago, # |
  Vote: I like it +87 Vote: I do not like it

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3 years ago, # |
  Vote: I like it +4 Vote: I do not like it

Fastest finger first

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Here's my 22 minute speedrun with solutions to all problems at the end. Enjoy :)

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Wonderful Contest!!

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Thanks for the contest!Interesting and good problems!

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

.

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    You are modifying the input strings themselves, pretty sure you can't do that.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Can organizers look into this issue. My rank states that I solved all question in 205 penalty and shows rank 265.
My rank
But the penalty of ranks around 260 is way too high and my name is also not in the ranklist.
Ranklist
Am I the only one or someone else also facing this issue ?

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

could not solve E,brute force obviously failed,though of merge sort but could not think how it will be impelemnted here.can someone help?

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    3 years ago, # ^ |
    ← Rev. 2   Vote: I like it 0 Vote: I do not like it

    Keep count of strings that end in character c and that start with character c. Also keep count of all strings in total.

    For any string s, remove it from the counts, add number of strings that end in s[1], number of strings that start with s[0], and subtract count of [s] to avoid overcounting in case s occurs more than once in the list.

    154325997

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3 years ago, # |
  Vote: I like it +8 Vote: I do not like it

LightspeedForces / HyperspeedForces

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Since got used to some tight time limits in harder problems I was trying to get a solution of each problem by using (if you will) smart strategy, but now I checked some other solutions and people just pass all test cases with 3, 4 for loops, bunch of while loops etc. :)

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

How to do E? I did a somewhat $$$O(n^2)$$$ solution and it gave me TLE.

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    3 years ago, # ^ |
      Vote: I like it -8 Vote: I do not like it

    combinatorics ig

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    suppose you are at index i, and you have stored all previous string instances in map

    if you have string ab at this index than

    you can change first char and check no. of occurrence of all such strings

    e.g. for ab -> bb, cb, — kb are such possible strings

    Similarly you can change second char and check no. of occurrence of all such string

    e.g. for ab -> aa, ac, ad ---- ak (after changing second char)

    just add all instances to your solution

    You can check my solution : https://codeforces.net/contest/1669/submission/154337766

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Thank you all!

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

where can i get today contest answers? i am curies to refer them

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3 years ago, # |
  Vote: I like it +9 Vote: I do not like it

Some will say this was a speedforces and this had not many interesting problems. But believe me when I was a beginner I always dreamed of a round where I could have solved more than 3 problems and that could have given me the gear that I was needing to accelerate my learning skills. For me this type of rounds should take place atleast once in every 1.5 months.

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

woohoo first time to experience the feeling of solving all the problems during a contest. it's way better than I thought

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3 years ago, # |
  Vote: I like it +7 Vote: I do not like it

self-deception forces

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

I answered question number b, But the site told me that the answer is wrong, please tell me where the mistake is my code is here https://codeforces.net/contest/1669/submission/154405569

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

Did you guys faced problem?codeforces was too slow for me.I was waiting for almost 5-10 minutes after clicking on one link.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Why this solution 154288735 WA?

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    You're mixing output streams (cout and puts) and they don't keep their order because the sync with stdio thing is set to false. I just commented that line and accepted.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

was this first div 4 round

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

Good contest see you all in other two years

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

When the rating is going to be reflected?

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

is it only me or the round actually previously stated rated for<=1400 Now says "do not have a point of 1400 or higher in the rating."

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    That is the condition of being a trusted a participant

    It is rated for you and everyone who has rating < 1400

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3 years ago, # |
  Vote: I like it +12 Vote: I do not like it

To not keep you waiting, the ratings are updated preliminarily. In a few days, I will remove cheaters and update the ratings again!

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Hi... I am receiving messages from the system that my solutions for this contest coincide with shrey_gta. I am sorry for my actions, but I have not done anything wrong or cheated. shrey_gta is my alternative id and I first gave my contest with that id only. Then after that, I submitted all the solutions in one go from my main handle. Also, this contest was not rated for this handle. I kindly request MikeMirzayanov to look into this matter and not block any my handle. I am again sorry for my actions and will not repeat those actions in the future. Thank You

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    3 years ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    BKL mike you can't be negative

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

why this sub 154484811 for F gives TLE ?

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    3 years ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    You should pass the vector argument to function bs by reference, not by value. The way you doing it it is copied each time.

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

Thanks for the authors, it was fun! Hope there will be more Div 4 contests in the future.

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3 years ago, # |
  Vote: I like it +4 Vote: I do not like it

I hope repeating this contest as the same as div 2 and div 3 Thanks for this amazing one!

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3 years ago, # |
  Vote: I like it +9 Vote: I do not like it

F in the chat for the codeforces rating predictor, it overpredicted everyone’s rating by almost 30

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3 years ago, # |
  Vote: I like it -15 Vote: I do not like it

This round should be unrated. I faced a lot of problems. Codeforces was too slow.Many times were wasted for this. After that I became bored and left the contest. It is not fair to rate this round. I even asked the authority whether it was my problem or their. They told they were trying to fix it.

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

Hello MikeMirzayanov My F problem is caught in plagiarism but have solid evidence that I don't stole it and I have solid proof. What should I do?

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Hello,

[user:SlavicG,MikeMirzayanov,][user:mesanu][user:Errichto] I got plagiarism on My F problem in this contest is coincedence and I have a solid proof about it. Now what should I do?_

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3 years ago, # |
← Rev. 3   Vote: I like it -12 Vote: I do not like it

.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I just the got the mail regarding palagrism.Your solution 154314647 for the problem 1669C significantly coincides with solutions Ashishpurbey/154314647, Ashishpurbey/154322351. 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://codeforces.net/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 block.

I hadn't copied any code from any where, I just submmit the same code twice and because of the glitch on codeforce it summited .They are comparing both code from the same ID and giving palagrism. So I requested you to visit this glitch one more time and retuned my rating back.

Your text to link here...

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    3 years ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    I'll fix all such issues after the global round or tomorrow.

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

      I got these messages but I don't know how these codes are similar. I have never done such things and also never got such messages before and what will I do after cheating in DIV-4 as it was already unrated for me;). MikeMirzayanov Please look into it.

      Attention!

      Your solution 154361635 for problem 1669G significantly coincides with solutions coder_vk/154361635, Daqlet/154366245. 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://codeforces.net/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.

      Solutions- https://codeforces.net/contest/1669/submission/154361635 https://codeforces.net/contest/1669/submission/154366245

      Attention!

      Your solution 154365782 for the problem 1669H significantly coincides with solutions coder_vk/154365782, Daqlet/154372523, bhadrayu_18/154412978. 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://codeforces.net/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.

      Solutions- https://codeforces.net/contest/1669/submission/154365782 https://codeforces.net/contest/1669/submission/154372523 https://codeforces.net/contest/1669/submission/154412978

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      3 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      MikeMirzayanov any good news about this issue ?

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      3 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      up up ⬆️

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

Hello,

I got a mail about plagiarism and I'm sure that this one is happened because of some coincidence or straight logic question.

MikeMirzayanov,SlavicG,flamestorm. I wrote code on my own and as you can see that in this submission 154392853 I got TLE on my submission and then I changed my code a little bit like this 154393751 and this one was accepted because of binary search has less time complexity.

PLEASE check out this. I hadn't copied any code from any where. So I requested you to visit this submissions and see what I changed in my code and got AC in my submission one more time and retuned my rating back.

check here

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