PurpleCrayon's blog

By PurpleCrayon, history, 6 weeks ago, In English

Hello Codeforces!

ijxjdjd and I are pleased to invite you to participate in Codeforces Round #728 (Div. 1) and Codeforces Round #728 (Div. 2) which will be held on Jun/25/2021 18:35 (Moscow time). Please note the unusual timing. Each division will have 5 problems and 2 hours and 15 minutes to solve them.

We would like to thank:

Read all of the statements carefully, and we hope you enjoy the problems! Wish you high ratings!

UPD: I would also like to thank Roberticey, golions, and kefaa2 for testing.

UPD: Here's the score distribution:

Div 1: 500 — 1250 — (1500 + 750) — 3000 — 3500

Div 2: 500 — 1000 — 1500 — 2250 — (2500 + 750)

UPD: The editorial is out!

UPD:

Congratulations to the winners!

Div. 1:

  1. maroonrk
  2. tourist
  3. Radewoosh
  4. LayCurse
  5. NotaMotuaQAQ

Div. 2:

  1. tampa
  2. CF_is_my_GF
  3. Apple_Method
  4. Skybytskyi.Nikita.2
  5. -this-is-obd-
 
 
 
 
  • Vote: I like it
  • +490
  • Vote: I do not like it

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6 weeks ago, # |
  Vote: I like it -395 Vote: I do not like it

Omg purplecrayon orz. Can't wait to solve your geniosity problems

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    6 weeks ago, # ^ |
      Vote: I like it -394 Vote: I do not like it

    Omg purplecrayon orz. Can't wait to solve your geniosity problems

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      6 weeks ago, # ^ |
        Vote: I like it -397 Vote: I do not like it

      Omg purplecrayon orz. Can't wait to solve your geniosity problems

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        6 weeks ago, # ^ |
          Vote: I like it -407 Vote: I do not like it

        Omg purplecrayon orz. Can't wait to solve your geniosity problems

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          6 weeks ago, # ^ |
            Vote: I like it -393 Vote: I do not like it

          Omg purplecrayon orz. Can't wait to solve your geniosity problems

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            6 weeks ago, # ^ |
            Rev. 2   Vote: I like it +204 Vote: I do not like it

            The comment is hidden because of too negative feedback, click here to view it

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              6 weeks ago, # ^ |
                Vote: I like it -220 Vote: I do not like it

              The comment is hidden because of too negative feedback, click here to view it

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              6 weeks ago, # ^ |
                Vote: I like it +43 Vote: I do not like it

              Don't steal my tricks. lol

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                5 weeks ago, # ^ |
                  Vote: I like it -24 Vote: I do not like it

                Thanks for the blog, hope to see u in purple next time ;)

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            6 weeks ago, # ^ |
              Vote: I like it -26 Vote: I do not like it

            Whatta coincidence! The sequence of their profile picture is like Mocha bear is rotating milk bear in some order :o

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

              that's the point... cf is tired of gyrating cats

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

                Is it a coincidence that the first question in div 2 contained gyrating cats. I am not into vodoo stuff but this sh*t is deep.

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                  5 weeks ago, # ^ |
                    Vote: I like it +11 Vote: I do not like it

                  well, purplecrayon is part of our gyrating cat club :P

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              5 weeks ago, # ^ |
                Vote: I like it +23 Vote: I do not like it

              Those are bears..? For so long I thought they were cats.

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

              .

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            5 weeks ago, # ^ |
              Vote: I like it -153 Vote: I do not like it

            It's a bad sight that the first five comments on the blog have all these negative votes!

            Suggest removing it, MikeMirzayanov

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6 weeks ago, # |
  Vote: I like it +144 Vote: I do not like it

I hope everyone enjoys our problems and learns something new!

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6 weeks ago, # |
  Vote: I like it +90 Vote: I do not like it

PurpleCrayon is a skilled programmer, and I'm excited to see the tasks he and ijxjdjd have prepared. Good luck to all participants, and hopefully we can see more crayon rounds in the future!

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6 weeks ago, # |
  Vote: I like it +46 Vote: I do not like it

Maybe I get purple on PurpleCrayon's round

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6 weeks ago, # |
  Vote: I like it +38 Vote: I do not like it

As a tester, give me ..

As a tester I can assure you that you will write purplecrayon orz after contest (before too)

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6 weeks ago, # |
  Vote: I like it +67 Vote: I do not like it

Each division will have 5 problems and 2 hours and 15 minutes to solve them. This line scares me.

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6 weeks ago, # |
  Vote: I like it -35 Vote: I do not like it

Why is the rating limit for Div.2 is 1899? Shouldn't it be 2099?

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6 weeks ago, # |
  Vote: I like it -37 Vote: I do not like it

Score distribution for this round will be really interesting I guess. 5 problems in 2:15 is very challenging

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6 weeks ago, # |
  Vote: I like it +25 Vote: I do not like it

Damn, 5 problems in 2:15 hours. Seems like a Div-1.5 :)

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6 weeks ago, # |
  Vote: I like it +31 Vote: I do not like it

If both divisions are 2 hours and 15 minutes why here the length is 2 hours?

Spoiler
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6 weeks ago, # |
Rev. 7   Vote: I like it -107 Vote: I do not like it

.

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6 weeks ago, # |
  Vote: I like it -34 Vote: I do not like it

Can't wait to see the geniosity problems !

purple orz .

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6 weeks ago, # |
  Vote: I like it -53 Vote: I do not like it

note the unusual timing.

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6 weeks ago, # |
  Vote: I like it +15 Vote: I do not like it

As a tester, I can confirm problems are awesome! Good luck in the round!

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6 weeks ago, # |
  Vote: I like it -66 Vote: I do not like it

Hope to be expert.

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

As someone purple did not allow test the round, give me contribution!

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    6 weeks ago, # ^ |
      Vote: I like it -56 Vote: I do not like it

    As someone purple also did not allow to test this round, give me contribution!

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6 weeks ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

As a participant, I hope my fellow comrade LostCoder16 and I can become purple in this PurpleCrayon blessed round, unlike last time. Wish us luck!! xD

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6 weeks ago, # |
  Vote: I like it +41 Vote: I do not like it

As a tester, I can say that I enjoyed the problems. Good luck to everyone participating :)

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6 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

I hope my colour change with a +ve delta :)

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

Unfortunately, most of IOI participants can't participate in this round :(

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6 weeks ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

I think upcoming contest was little bit tricky..so,I hope u all are enjoying this contest and learns something new!

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6 weeks ago, # |
  Vote: I like it +17 Vote: I do not like it

Excited for the round, knowing the writers I have no doubt it will be great!

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6 weeks ago, # |
  Vote: I like it -23 Vote: I do not like it

i expect if I participate, i will get green in this round :)

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

I wish problem statements would be as clean as this announcement

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    6 weeks ago, # ^ |
      Vote: I like it +45 Vote: I do not like it

    I wish statements would be as short and clear as the annoucement, too.

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6 weeks ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

.

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6 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

I wish that this contest has Graph theory and DP related problems !

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6 weeks ago, # |
  Vote: I like it -54 Vote: I do not like it

66.

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6 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Why do the recent contests take place in unusual time...

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

I will remember the contest start time properly this time, the previous contest div 2 which I thought usually to start at 20:05 but it was around 3pm RIP

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

PurpleCrayon is not even purple Sadge

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5 weeks ago, # |
  Vote: I like it -84 Vote: I do not like it

I will not take part in this contest just because of unusual time!!

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5 weeks ago, # |
  Vote: I like it -11 Vote: I do not like it

"You, for participating!" This line hit hard :(

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5 weeks ago, # |
  Vote: I like it +20 Vote: I do not like it

As a cyan, D seems not killable.So, speedforces :(

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5 weeks ago, # |
  Vote: I like it -51 Vote: I do not like it

As a tester,who wasnt able to solve a single problem

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

Really excited to participate in div2.. All the best everyone.

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5 weeks ago, # |
  Vote: I like it -32 Vote: I do not like it

Benq only competes when he knows he will get first. Otherwise, he doesn't compete to protect his rating. Conspiracy?

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

The scoring distribution for div2 is weird. I hope I get positive delta.

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5 weeks ago, # |
  Vote: I like it -9 Vote: I do not like it

I hope i can solve at least 3 questions.

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5 weeks ago, # |
  Vote: I like it -39 Vote: I do not like it

The contest timings 20.05 IST were better. Hope it changes from next contest.

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

Can anyone tell what does (1500 + 750) mean in the score distribution? Does that mean the score of the question can be (1500 or 750) or does that mean the score would be 2250?

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

    It means the problem has an easy version and a hard version. Solving just the easy version would give you a max 1500 score, solving both would give you a max 2250 score.

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

      Why does the easy version has a higher rating than the hard version?

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

        This is a fine move by the setters so that we lame programmers can feel better.

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

        Why it shouldn't be?

        The complete score is the score of the "hard version". Easy version should be considered as partial score for partial solution. If it contains significant part of the final solution, it is natural that is worth significant part of the final score.

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

Hope that I can become a crayon today ^_^

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

hope i can solve 1 or 2 question

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

Is it logical that the second part of the last problem of div2 has the same score as in div1 (750)?

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

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

how to solve D when you are green?

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

So are we solving E2 after A?

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

    Went with that approach at start. Only to return back sad faced after reading E1 fr 5 mins. T_T . Dumb me!!

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

I wish everybody an awesome codeforces round

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

gl

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

i think today i become pupil

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5 weeks ago, # |
  Vote: I like it +45 Vote: I do not like it

Anyone in Div 2 feeling like they accidentally participated in Div 1?

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5 weeks ago, # |
  Vote: I like it +30 Vote: I do not like it

Speedforces, redefined.

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5 weeks ago, # |
  Vote: I like it +15 Vote: I do not like it

The game of hand speed.

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5 weeks ago, # |
  Vote: I like it +87 Vote: I do not like it

The expected value to solve D by myself is 0.

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5 weeks ago, # |
  Vote: I like it +36 Vote: I do not like it

Most difficult div.2 D ever?

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5 weeks ago, # |
  Vote: I like it +36 Vote: I do not like it

Never seen such a big jump in difficulty from C to D

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

What is Normal Red?

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5 weeks ago, # |
  Vote: I like it +17 Vote: I do not like it

Div 2 is definitely a speed force.

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

speedforces

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5 weeks ago, # |
  Vote: I like it +60 Vote: I do not like it

I have no idea on 1B or 2D, wtf

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5 weeks ago, # |
  Vote: I like it +260 Vote: I do not like it

Some relavant meme:

1624641267990-1

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    5 weeks ago, # ^ |
      Vote: I like it +17 Vote: I do not like it

    I want to give 200 upvotes T_T

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    5 weeks ago, # ^ |
      Vote: I like it +17 Vote: I do not like it

    E1 is like Atcoder grand contest math problem.

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5 weeks ago, # |
Rev. 2   Vote: I like it +19 Vote: I do not like it

ive read all the problems and they are really nice good job!

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

Solved 3! Then saw D. WTF only 13 submissions!?

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    5 weeks ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    Started with D, read it & thought something, then saw A. WTF crossed 10,000 submissions!?

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5 weeks ago, # |
Rev. 2   Vote: I like it -9 Vote: I do not like it

Forget about it

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    5 weeks ago, # ^ |
      Vote: I like it +27 Vote: I do not like it

    It's probably hard to solve problems when you are creating memes during the contest.

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      5 weeks ago, # ^ |
        Vote: I like it +48 Vote: I do not like it

      There must be more than 16k people creating memes, because only 15 people could solve the problem

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

I feel like this was speedforces but at the same time wasn't speedforces :)

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

So by Div 2 u meant Div 1.5

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5 weeks ago, # |
Rev. 3   Vote: I like it -7 Vote: I do not like it

Good and challenging problems ! Good job but the difference of difficulties of problems between c and d was a lot !

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5 weeks ago, # |
  Vote: I like it +65 Vote: I do not like it

Literally 15 mins on 1A and 2 hours on crying

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

Screenshot-20210625231411-140x49

That sums it up :(

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5 weeks ago, # |
  Vote: I like it +14 Vote: I do not like it

I hate probability.

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5 weeks ago, # |
Rev. 3   Vote: I like it +1 Vote: I do not like it

Me in Div2 today:

First, solve three problems.

Second, look at the accepted number of problem D

Third, give up and go to the comment section.

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

DIV-2: When I solved B there were ig 200-300 people who solved C, When I solved C there were 2 people who have solved D. Got the idea about the question before reading it.

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

    Can you share your approach to DIV 2 b ?

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

      just brute force over numbers that i+j = input[i] * x, where x is any natural number.

      for example: input: 3 1 2 4 5

      3 is at place 1, so u can take only number 2, 5, 8 etc. because u won't be able to get number not divisible by 3, if u multiply 3 by anything, so just check numbers that after summing gives number divisible by it

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      5 weeks ago, # ^ |
      Rev. 4   Vote: I like it 0 Vote: I do not like it

      Iterated i from 1 to n-1; We have to find the all the possible (j>i) & (j<=n) which satisfy the given condition.

      For this number at ith position. i+j can range from i+i+1(a) to i+n(b);

      v[i]*v[j] = i+j.=> We have v[i] and range of i+j in hand. So what is the possible range of v[j]? ((a/v[i]) + (a%v[i]==0?0:1)) (c) to (b/v[j]) (d);

      Now iterate from c to d (possible v[j]) and find whether the number in this range exist at respectively jth index, such that a[i]*a[j] = i+j;

      Take sum.

      Time complexity should be O(n). The range of c-d is maximum when a[i]=1 ~ n but since all numbers are different so if at next index a[i]=2 then range of c-d shuld be n/2 . Now n+ n/2 +n/3 + ... ~ O(n)

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

        Probably sum of n + n/2 + n/3 + ... is O(N*logN), as harmonic series (without n factor in each summand) is equivalent to logarithm. But yeah, that is still AC :)

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

Am I the only that forgot numbers in B are distinct and wasted more than 20 min because of that

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5 weeks ago, # |
  Vote: I like it +14 Vote: I do not like it

Seems like I'm getting dumber with each passing day, half of the world solved C in one go.

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

    :) while I could not able to solve it.

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

      :( another rough day for us

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

      Same here :(

      I wonder how 4k+ people solved C. Was it that easy?

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

        same old story..solutions were available for free on internet

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

    for me it was pretty hard to understand the problem for first 10 minutes, then it went from graphs -> dp -> sorting and turn out to be easy problem lol

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

    I get wa on both A and B :( ,same pinch bro,I also feel same

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5 weeks ago, # |
Rev. 3   Vote: I like it +8 Vote: I do not like it

What should the answer be for the 3rd example testcase for div2D? I got 141/40 = 925000010 but it should be 500000007. What's the actual fraction that gives 500000007 though?

agh i think i figured it out.. I was computing the probability of marking X before Y, given the heights from the root of X and Y, but it really should have been the heights from the LCA of X and Y, not from the root. :(

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

Thanks for the contest! I really enjoyed it.

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5 weeks ago, # |
  Vote: I like it +71 Vote: I do not like it

The maximum boring problem set in Div2. Three observation based problems, and D + E ridiculously difficult. The contest was practically over after 20 minutes.

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5 weeks ago, # |
  Vote: I like it +6 Vote: I do not like it

ok ...i hate my life now

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

I entered 25 minutes later and after 35 minutes I left by topping in my room! This line describes the contest!

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5 weeks ago, # |
  Vote: I like it +98 Vote: I do not like it

MEET AN EXPRIENCED & SHAMELESS CHEATER This is how kedos123 bypasses Plagiarism testing.

i reported to codeforces and MikeMirzayanov about him from past 2 contest and he does cheating in it also and got plagiarism , thanks to u for upvote my comment so that he got punished . and today again he cheated in the contest , pls again upvote my comment ......

kedos123 does cheating from starting and i reported about it to MikeMirzayanov and he got plag in last 2 rounds , he abused me in private chat becz i reported him https://ibb.co/JmhSwKL . guys show your support and again upvote my comment so he again got punished.

People like kedos123 are spoiling the sport. I don't understand where would cheating take them in life. They will never get anywhere in life but always remain what they are i.e cheater. He should be banned from the platform as soon as possible . MikeMirzayanov sir pls ban him and skip his solutions .

his todays contest submission 120565019 120557120 , saw his submission timing and also see this dummy variables snippet

xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++;xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++; xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++;xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++; xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++;xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++; xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++;xx[3]++;xx[1]++;xx[3]--;xx[1]--;xx[5]++;

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

Can anyone explain Div2 problem C

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

    sort the number in increasing order, then just for every 0<=i<n subtract every number j that 0<=j<i

    so: input: 0 2 1 3 5 15

    sort: 0 1 2 3 5 15

    5-15 + 3-15 + 2-15 + 1 — 15 + 0-15 + 3-5 + 2-5 + 1 — 5 .. etc

    Idea is go to the highest number first, then u can achieve every smaller number by subtracting something from it

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5 weeks ago, # |
Rev. 3   Vote: I like it 0 Vote: I do not like it

..

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

My logic for C, take the sum of differences of all pairs and subtract the difference of adjacent elements from it and print the answer with a negative sign. Why is this failing?

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

    The answer is take the absolute differnce of each pair and then subtract maximum value from array d and then multiply with. 1 , The logic is that to minimise the cost you should add as many -ve no. You can and as less +ve no. You can , So for +ve no. you will take maximum no. As the sum of difference between adjacent sorted no. will lead to it and for -ve add All -ve no.s .

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

      Found the mistake in my solution. Missed sorting. Just adding that and submitting again gave me an AC :(

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5 weeks ago, # |
Rev. 3   Vote: I like it 0 Vote: I do not like it

How to solve B ? I don't know how it can be solved in o(n)

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

    It's not O(n). Rewrite the eqn as aj = (i+j)/ai

    Now, as aj is an integer, i+j must be a multiple of ai, you need to check only ai blocks in each case. Since ai is distinct, this is similar to prime sieve in terms of time complexity.

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

      Yes I got your point ! actually i spent so much time trying to make it only O(n) and i couldn't

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

    Ok now i feel dumb ,All of that time i thought if used another for loop with i+=array[i] as a step it will be more than o(n)

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

    For any $$$a_i$$$, we need $$$a_j = (i+j)/a_i$$$. Hence you only have to look at all $$$j$$$ such that $$$i+j$$$ is divisible by $$$a_i$$$ instead of all the $$$n$$$ elements. Note that since there are n elements and $$$1<=a_i<=2n$$$, and all elements are distinct, at worst it will take $$$O(n+n/2+n/3+..)$$$ or $$$O(nlogn)$$$ complexity.

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    5 weeks ago, # ^ |
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    Let us start with the brute force approach..

    You would initialise two for loops.. one from i (1 to n) and the inner one j (i+1 to n) .. iterating over all values and obtaining all such pairs. However, this would take order of n*n and is not feasible.

    So, the key observation is it can be reduced to approximately nlogn per testcase, by only considering the valid indices that occur after i that are themselves multiples of a[i] , incrementing j by a[i] each time. The first such j for which i+j is a multiple of ai can be found by simple math (because ai*aj=i+j, so i+j has to be a multiple of ai).

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      5 weeks ago, # ^ |
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      I feel more dumb now because i got the same idea but thought it would give TLE ; _ ;

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        5 weeks ago, # ^ |
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        It would indeed give tle if all elements of the array were not unique.. as it would now tend towards n*n for big n and small ai.

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    5 weeks ago, # ^ |
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    Based on what I observed in my room, there were 2 major ways to solve B: Either an $$$O(n\sqrt n)$$$ solution or $$$O(nlogn)$$$, which I thought was pretty cool.

    $$$O(n\sqrt n)$$$:

    First, create a map $$$where[n]$$$ for all $$$a[i]$$$ -> $$$i$$$. Now, iterate over all integers $$$i$$$ from 1 to $$$2n$$$. Get the factors of each integer $$$i$$$. Now, for each factor $$$f$$$, check if $$$where[f] + where[i/f]$$$ = $$$i$$$. If so, increment the answer.

    $$$O(nlogn)$$$:

    We iterate over every multiple $$$k$$$ of each $$$a[i]$$$ and check if there exists an index $$$j$$$ where $$$j > i$$$ and $$$j + i = k$$$. If so, check if $$$a[j] = k$$$. If so, increment the answer. This works since all $$$a[i]$$$ are distinct, so the time complexity is bounded by the harmonic series $$$n (1 + \frac {1}{2} + \frac {1}{3}...)$$$ which is well known to have an upper bound of $$$O(nlogn)$$$.

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    5 weeks ago, # ^ |
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    I think most of the people first tried to solve it in O(n). That's why submissions were late.

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5 weeks ago, # |
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How to solve problem C ?

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    5 weeks ago, # ^ |
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    Sort the input as the order of pastures doesnt matter.

    Then notice that more the roads between pastures more minimal the time will be.

    Now create a difference array from the sorted array as they will correspond to our postive edges in graph.

    Now we take make negative edges for every pair of pastures.

    The sum of these will be the negative of sum of all subarrays of difference array(Call it NEG). This can be calculated in O(n) using contribution technique.

    So final answer would be sum of positive edges(all elements in difference array) + NEG.

    This is greedily the minimal ig. You can check my submission out. I feel it is neat.

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      5 weeks ago, # ^ |
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      A question about the problem C div 2. The parsing says: Instead, you can sort d and calculate the contribution of each node to the answer. Please explain how to count the contribution of each node in the answer in more detail. You can use an example. Thanks.

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    5 weeks ago, # ^ |
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    Note that you need to arrange the vertices in such a way so we minimize the sum of positive edge, which can be done by sorting the array and taking minimum times to be a difference of two consecutive elements.

    Eg:- $$$w x y z$$$ be the sorted array then $$$(x-w), (y-x)$$$ and so on will be the costs of edges which gives a path from patch 1 to all patches with minimum positive cost.

    Now we can need to add negative backward edges to make the total sum of each cycle zero. Let us say the edges are $$$a,b,c,d,e$$$. Then the negative edges cost will be $$$N=(a+b+c+d+e) + (a+b+b+c+c+d+d+e) + (a+b+c+d+b+c+d+e) + (a+b+c+d+e)$$$. Each term corresponds to nullifying cycles of with 2,3,4 and 5 vertices respectively. Generalize the summation for $$$n$$$.

    The answer would be $$$a+b+c+d+e-N$$$.

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      5 weeks ago, # ^ |
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      I really don't understand how you do it

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        5 weeks ago, # ^ |
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        Here the cost of each curved arc will be a negative value such that the total cost of its respective cycle becomes zero.

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          5 weeks ago, # ^ |
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          Farmer John guarantees that it is impossible for the cows to get stuck in a time loop, where they can infinitely go back in time by traveling across a sequence of roads.

          can u explain where does the above statement play a role in your solution? As I thought that it doesn't allow more than one longest cycle to form in the graph.

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            5 weeks ago, # ^ |
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            "As I thought that it doesn't allow more than one longest cycle to form in the graph." ==> It does not allow a cycle with the total sum of edge weights < 0.

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              5 weeks ago, # ^ |
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              Ahhh... Thanks for clearing the doubt as it kept bugging me during the contest and couldn't ask the author the same thing during the contest thought it might violate any rules..

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5 weeks ago, # |
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Is there any chance to pass Div.1 D by $$$O(n^2 \log n)$$$ solution...? I know $$$3e9$$$ per second sounds insane :(

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5 weeks ago, # |
Rev. 3   Vote: I like it -36 Vote: I do not like it

Hello! Nice problems but the leveling of the questions was not very good. D Div2 was very hard

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5 weeks ago, # |
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Div2D was so hard, only 18 people solved it.
I thought of doing something like this:

For the tree rooted at $$$i$$$, what's the probability that node $$$j$$$ is reached before node $$$k$$$?

And inversion counting like that, but I didn't work out the details of how to figure that out.
Was the intended complexity $$$O(N^3)$$$?

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    5 weeks ago, # ^ |
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    ah, that was my idea too! I coded it up but got WA on the example pretest #3 :(

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    5 weeks ago, # ^ |
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    It might be possible to do it in $$$N^3$$$ but my solution was $$$O(N^3\text{log}N)$$$. The bottleneck was finding the $$$O(N^2)$$$ lca's for each pair of nodes given a fixed root.

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    5 weeks ago, # ^ |
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    I asked instead:

    Given nodes $$$i$$$ and $$$j$$$, what is the probability that $$$i$$$ comes before $$$j$$$?

    This leads to an $$$O(N^3)$$$ solution. However it took me 2 hours past the end of the contest to correctly work out how to implement it.

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5 weeks ago, # |
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How to solve Div 1C/2E?

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    5 weeks ago, # ^ |
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    it seems that initial array is valid if and only if $$$\sum_{i=1}^k a_i \ge \sum_{i=1}^k (x+s_i)$$$ holds for all $$$1 \le k \le n$$$, where $$$s_i=\sum_{j=1}^{i-1} b_j$$$. But I have not submitted, so i have no idea if there is anything wrong or not.

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5 weeks ago, # |
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I still didn't get what is the notes he's referring to, in Problem E1.

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5 weeks ago, # |
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Couldn't submit 1B by 10 seconds :(

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5 weeks ago, # |
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Well I'm glad to see I wasn't the only one having trouble with 2D. It's a nice problem though, I think I have a solution but it will take me a few hours to implement it.

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5 weeks ago, # |
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Biggest drop of my contest history. Well, worth a fall if I hope to perform well again!

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5 weeks ago, # |
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Felt like the entire contest was me making little progress on C1 and secretly hoping the solve count would stop rising :P at least I did well in the speedforces race.

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5 weeks ago, # |
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when will the ratings be updated ? any ideas?

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5 weeks ago, # |
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How to solve div-2 D ??

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5 weeks ago, # |
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Anyone remember when galen_colin said that your rank can really depend on the time you take to solve the problems? Welp, it's even more severe this contest, being from positions 19 - 4269 (approx).

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5 weeks ago, # |
  Vote: I like it -15 Vote: I do not like it

PurpleCrayon, I liked the problems a lot, but I think that most of Div. 2 participants will disagree and say that it was not very balanced, turning things into speedforces somewhat

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5 weeks ago, # |
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Where can I find it's solution!!!!! Can anyone tell me??????

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5 weeks ago, # |
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Pure speedforces

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5 weeks ago, # |
Rev. 3   Vote: I like it -7 Vote: I do not like it

c

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    5 weeks ago, # ^ |
    Rev. 3   Vote: I like it +8 Vote: I do not like it

    Because you have UB, you're accessing index out bound, your array is not big enough

    For heaven's sake. If you're writing code in c++ you should know about UB and consider it whenever something inexplicable happens

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      5 weeks ago, # ^ |
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      thanks for pointing out. I know about UB but i missed it completely out of frustration.

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5 weeks ago, # |
Rev. 2   Vote: I like it -19 Vote: I do not like it

Check out time complexity for problem B

If anyone has better approach then you can add here

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

The problems are pretty good,but the diffculty gap between Div2 C and Div2 D are too big,making this Div2 round a "speedforces" round,so to my opinion,not very enjoyable because the round is not very balanced. Again,the contest is great,but I think there are room for improvements.

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5 weeks ago, # |
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how to solve B div2

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    5 weeks ago, # ^ |
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    Iterated i from 1 to n-1; We have to find the all the possible (j>i) & (j<=n) which satisfy the given condition.

    For this number at ith position. i+j can range from i+i+1(a) to i+n(b);

    v[i]*v[j] = i+j.=> We have v[i] and range of i+j in hand. So what is the possible range of v[j]? ((a/v[i]) + (a%v[i]==0?0:1)) (c) to (b/v[j]) (d);

    Now iterate from c to d (possible v[j]) and find whether the number in this range exist at respectively jth index, such that a[i]*a[j] = i+j;

    Take sum.

    Time complexity should be ~ O(nlog(n)). The range of c-d is maximum when a[i]=1 ~ n but since all numbers are different so if at next index a[i]=2 then range of c-d shuld be n/2 . Now n+ n/2 +n/3 + ... ~ O(nlog(n))

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    5 weeks ago, # ^ |
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    For each element you can find the number of elements that have product less than 2*n that is max(i+j). By mathematics you can prove that total such pairs are not more that nlogn. Hence brute force will work under time limits.

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    5 weeks ago, # ^ |
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5 weeks ago, # |
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Where are those cats with their generosity problems now?

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5 weeks ago, # |
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The gap between div2-C and div2-D is too large so if u submit some wrong answers in the first three questions u get a bad rank...

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5 weeks ago, # |
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First time to solve a problem as difficult as div1D!

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5 weeks ago, # |
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This is the most difficult Div.2 problem D I have ever seen.

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5 weeks ago, # |
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120609085 my sweet O(NQ) solution has passed... :)

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5 weeks ago, # |
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Can somebody post the screen with Swistakk's comment about $$$O(n \cdot \sqrt{n} \cdot \log(n))$$$ vs $$$O(n^2)$$$, please?

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5 weeks ago, # |
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Is there going to be a hacking period?

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5 weeks ago, # |
Rev. 3   Vote: I like it -28 Vote: I do not like it

why downvotes?

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    5 weeks ago, # ^ |
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    Multiple reasons for you getting downvotes.

    1. You didn't even mention which problem. Man, how do you expect to get help?
    2. Second, no one is going to voluntarily debug your code (unless he is too kind). There is a certain approach to ask for help. That is to share your logic, and people will find out what you are missing.
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5 weeks ago, # |
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What I don't like about observation problems that it is too easy to cheat and too difficult to catch the cheaters

And this was like all the problems were observation based

Even though I kind of tired of cheaters topics as well

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5 weeks ago, # |
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How to solve D? Can anyone explain? Never seen such a big difficulty jump between C and D.

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How to prove the correctness of problem C's solution?

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5 weeks ago, # |
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Auto comment: topic has been updated by PurpleCrayon (previous revision, new revision, compare).

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5 weeks ago, # |
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the round wasn't balanced :(

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5 weeks ago, # |
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how to solve D?

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5 weeks ago, # |
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Very enjoable contest! Very enjoable not math tasks! Very enjoable raiting everybody've gained! Very enjoable enjoy i've felt. Good job! Good job! Good job!

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5 weeks ago, # |
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Can someone please explain solution to C problem

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5 weeks ago, # |
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Did anyone noticed weird template of this guy tampa (Rank 1 in today's div 2 contest)

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    5 weeks ago, # ^ |
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    I think he is simply using the atcoder library templates.

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5 weeks ago, # |
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I think that we should make the problem more clearly or at least give us more example to understand what exactly we have to solve. It's not funny when you read a long text and understand nothing :((

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5 weeks ago, # |
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Diego nice

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    5 weeks ago, # ^ |
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    I never understood how it happened

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      5 weeks ago, # ^ |
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      Do you mean that you don't know what "Unexpected verdict" means?

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        5 weeks ago, # ^ |
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        Yes. And I don't know, why it happened on my hack

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          5 weeks ago, # ^ |
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          You've hacked the model solution (it got TLE or RE, probably TLE here).

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            5 weeks ago, # ^ |
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            Oh, realy nice!

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              5 weeks ago, # ^ |
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              Well, I'm not that sure, it should not happen if everything would be prepared correctly, but shit happens. And yep, for you it's nice :P

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                5 weeks ago, # ^ |
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                Maybe "shit" is too much actually. I that guess it means that one of the solutions marked as a correct one got TLE, it doesn't mean that the main one got it.

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              5 weeks ago, # ^ |
                Vote: I like it +49 Vote: I do not like it

              One of slowest solutions we considered correct, to be precise. But it doesn't belittle your achievement, congrats!

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    5 weeks ago, # ^ |
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    Hey Radewoosh please tell me how to solve div-2 D (div-1 B)

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      5 weeks ago, # ^ |
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      Sure. Read the statement, then start thinking about the solution.

      EDIT Or read the editorial.

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5 weeks ago, # |
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Whats-App-Image-2021-06-26-at-12-08-24-AM

:'/

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5 weeks ago, # |
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5 weeks ago, # |
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My nice explanation of Problem B and check out problem A also.

https://www.youtube.com/watch?v=frb_ngCPXOg

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5 weeks ago, # |
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This round, Will be rated?

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5 weeks ago, # |
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Guyjj and gals ! Probmle A, Nice and smooth explanation here !

https://youtu.be/Me6sGr9s5FM

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5 weeks ago, # |
Rev. 2   Vote: I like it -6 Vote: I do not like it

MikeMirzayanov PurpleCrayon I received a plagiarism notice. But I don't know on what basis I got the Plagiarism. I dont even know him and A problem was so simple that one can have exact same code since we only need to swap the elements adjacent element and swap the last 2 element if it is odd.. Many could have thought the same solution .. Please Look into this.. I wouldn't consider it a plagiarism! I have given like more than 50 contest and why would i do this kind of thing !! His code is same as mine because thinking was same and it was an easy problem . Please Look into this ..

This is what I got from you guys !

Attention!

Your solution 120540551 for the problem 1541A significantly coincides with solutions phoenix_slayer/120540551, vedant.gupta.cer20/120587528. 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.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.

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    5 weeks ago, # ^ |
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    Did you get any solution from system yet? phoenix_slayer

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      No not yet.. But I got my rating change!! But still there's a warning which I would like to get removed from them!! Like A question always have same kind of submissions and don't know why they plagiarised!! I don't think they will correct it!!

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5 weeks ago, # |
Rev. 5   Vote: I like it -16 Vote: I do not like it

...,,..

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    5 weeks ago, # ^ |
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    ...

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      5 weeks ago, # ^ |
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      You can say you didn't cheat and can ask for not to give any punishment. But why you will be in huge pain and stress just because of loosing some rating?.do you think life is that much cheap??

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      5 weeks ago, # ^ |
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      solution 120576906 for the problem 1541C significantly coincides with solutions kritarth2121/120575849, kritarth21/120576906

      You have participated in the contest using two accounts and this is forbidden by the rules.

      If kritarth2121 is actually some imposter rather than your alt account, then the obvious code similarity is very suspicious. What are the chances to have similarly named accounts submitting similar solutions just accidentally?

      just because of same function which is written to avoid plague took me into plague

      Code obfuscation is also forbidden by the rules. Even though this is not actively enforced yet.

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    5 weeks ago, # ^ |
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    I am removing this comment now . I don't want to give him more mental stress but i am hoping that he will never cheat again.

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5 weeks ago, # |
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Sorry but it was a coincidence .. I published my code on ideone.com that's why the problem has occured. Please give my ratings back and i hope you can see that i have made 2 attempts which gave a TLE and hope you can recoganise it. if i were to cheat i wouldnt have made wrong attempts.hope to get rigth decision fron codeforces. thankyou

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5 weeks ago, # |
Rev. 3   Vote: I like it +1 Vote: I do not like it

Nowdays codeforces solutions are available in net during contest. Someone are getting ideas from live streaming and someone are getting direct code. I don't know what do you want to achieve by cheating? Rating? Show some courage. The problem solvers who are practicing hardly they won't get a correct rating for your cheating during the contest.

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5 weeks ago, # |
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Hello codeforces, I was using ideone.com as I did not have my personal machine, and I think that's the reason that this problem has occurred. I have been sincere in my attempts for this as well as previous contests and I will ensure that I don't use ideone.com again. Thank you.

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    5 weeks ago, # ^ |
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    This is your mistake. Just do another contest and achieve ratings

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Congratulations to tourist for winning second place!

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5 weeks ago, # |
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Where is contest's rate Lol

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5 weeks ago, # |
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Hey MikeMirzayanov I received following system message regarding plagiarism in both of my code submission-

Your solution 120549299 for the problem 1541A significantly coincides with solutions manvi2912/120544816, Action_Kamen/120549299, satejansh/120561800

This is definitely an error on the part of the system because 1) I didn't cheat a single line from anyone 2) If you check the time taken by the system on concerned submission all time taken are different 3) I was using a predefined template for both of my submissions, which is different from the template (or boiler plate) code used by other submission 4) In the problem B I submitted using a map but none of the above submission used map. 5) While some of the code for A might be matching that is due to sheer luck as the variable used are quite general such as t to test case i for loop counter( logic in the question was also pretty straightforward)

So please, MikeMirzayanov do the needful as I am working hard for this and also after a long time any of my contest went well.

Thank You

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5 weeks ago, # |
Rev. 6   Vote: I like it -15 Vote: I do not like it

Your solution 120588348 for the problem 1541A significantly coincides with solutions jatin3028/120548283, Saitama1227/120548701, TheBeardedCoder/120549565, yog_111/120550555, Ali_salloum/120550818, Atom_Bomb/120559071, phoenix639/120560190, sanskar00/120562876, Astro_Aditya/120563489, reshma_27/120569500, Dilip24/120573780, Shalika22/120582653, Farhan_meb/120588348, Paavan_parekh/120595630, Dlip/120597081. 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.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.

Hello, so i received a message saying my solution for a got matched with some random people. I am quite surprised to realize how could you judge a straight forward a problems solution as plag as the solution was change the indexing with its near index and that's it. And you can also check my ip or somehow if i have multiple accounts at contest time. This is totally unfair as i have solved b,c and didn't get plag but got you judged i copied some easy problem a. Please check this matter out. Got -184 which is quite a big deal for me. MikeMirzayanov. I dont even know any of the mentioned persons.

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

    Seeking your kind attention!!! MikeMirzayanov I hope you will look into this matter. About submitting an easy problem so late, i was busy solving C and B first, this is why i solved A at last because B and C mattered to me much as A was straight forward problem and i knew everyone who participated the contest could solve it with 1 less than 1 month of experience. Please, Check this out.

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

      No brother.. Rather say that,you got the solution of B and C first and you made a slight change so that plag detector Won't catch you and at last you got A and you didn’t change it much. Lol.have some brain before cheating.

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

        Do you even know me bro that you are so sure about your accusation? WHO basically needed solution for A? Kindly check my profile and then say that, i finally got solution for A!!!!! and then didnt change it!!!! Kindly stop creating new accounts and scamming please. This community is becoming full of scammers day by day!

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

          Your solution for C and B is exactly same as the leaked code(you know but wont confess)and you just changed a little bit. I saw you just started doing good in last few days.Why you needed to cheat in this circumstances.you could hold a little bit for your rating to continue in expert rather than cheating. Such a shame

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

            So you saying i copied b,c and changed the codes. But didn't bother to change code of A? Makes sense? Who would be this dumb bro? I literally have no idea what leaked code you are talking about tho. Ideas can match of a solution!

            This is why we should record while participating a contest as a emergency proof. Gonna do it from next rounds though!

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

              Sorry to say but you submitted all three with a delay of 8 and 7 mins, that clearly shows you got the answer and just uploaded them after few changes but unluckily you got plag. in A.(But you will not accept it)