Mo2men's blog

By Mo2men, history, 4 months ago, In English

Hello, Codeforces!

I'm glad to invite you to Codeforces Round #737 (Div. 2) , which will be held on Monday, August 9, 2021 at 16:35 UTC+2.

This round rated for the participants with rating lower than 2100.

You will be given 5 problems and 2 hours to solve them.all problems were prepared by me and AhmedEzzatG.

One of the problems will be interactive. So, it is recommended to read the guide on interactive problems before the round.

I would like to thank -

  1. Aleks5d, for awesome coordination of our round and suggested one of the problems.

  2. Kaneki-kun for help us to prepare the problems. compiler_101 ,Shanks ,DeadPillow , and Omar_Elawady for discussing and testing the problems.

  3. MikeMirzayanov, for the amazing Codeforces and Polygon platforms.

  4. Testers physics0523 , BlueDiamond , Tlatoani ,mahmoudbadawy , Andreasyan , IsaacMoris , Error_404 , Basilhijaz , hu_tao , m371 , Blobo2_Blobo2 , elizkaveta , zetamoo , Mohammed_Atef_Hassan , tdpencil , mcdx9524 , nGu , _Hosam , Bakry_ , N4553R , rkm62 , Hemose , Uzumaki_Narutoo , and our VIP tester 1-gon.

The statements are short and I have tried to make the pretests strong. I encourage you to read all the problems.

This is our first official round on Codeforces. We are sincerely looking forward to your participation. We hope everyone will enjoy it.

Good luck and see you in the standings!

UPD1: I want to thank Aleks5d for translating statements into Russian and mouse_wireless author of one of tasks.

UPD2: Scoring distribution: 500 — 1000 — 1750 — 2500 — 3000

UPD3: Editorial

UPD4:

Winners

Congratulations to all our winners in the round!

Div.1 + Div.2:

  1. tourist

  2. jiangly

  3. m_99

  4. BigBag

  5. Geothermal

Div2:

  1. treborr

  2. juruo_cjl

  3. RGB_ICPC4

  4. zxcgod

  5. Hanabi2333

 
 
 
 
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4 months ago, # |
  Vote: I like it +41 Vote: I do not like it

Your profile picture is really good and meaningful.

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

i am very happy, you are amazing men #keep going ♥♥

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4 months ago, # |
  Vote: I like it +125 Vote: I do not like it

1-gon was the VIP tester of 2 consecutive rounds!

Orz!

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

As a trainee for the author I am so excited and I am sure that the statements are short XD

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

iam waiting for a great contest

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

keep going from ur trainee.

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

As a trainee for the author I am so excited and I am sure that the contest will be amazing as the author is amazing XD

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

Amazing!! It will be such a great contest!

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

I'm excited! We are in a drought of contests, and I'm itching to compete more.

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4 months ago, # |
  Vote: I like it +27 Vote: I do not like it

As a tester, problems are great for the participants who love the short statements and like to gain high ratings!

Good luck to everyone :)

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

Finally a SA3EDY Round #1، I hope it will not be the last one. keep going our heroes♡♡ ♡‿♡.

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

Egypt Foooooo2 :"D

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4 months ago, # |
  Vote: I like it +64 Vote: I do not like it

As a very cool tester, I would like to say that the problems are nice and the pretests are very strong. I think you'll enjoy doing this round.

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    4 months ago, # ^ |
    Rev. 3   Vote: I like it +52 Vote: I do not like it

    So, shamelessly give me contribution.

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      4 months ago, # ^ |
        Vote: I like it +35 Vote: I do not like it

      commenting again instead of editing, double contribution, smart move xD

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4 months ago, # |
  Vote: I like it +113 Vote: I do not like it

with the power vested upon me as a tester, I hereby declare thy contest interesting.

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4 months ago, # |
  Vote: I like it +195 Vote: I do not like it

Though I'm not a VIP tester, I tried hard testing as much as I can.

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    4 months ago, # ^ |
      Vote: I like it +57 Vote: I do not like it

    Yes, I can assure that you did a great job.

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

    What's the difference between tester and VIP tester?

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      4 months ago, # ^ |
        Vote: I like it +85 Vote: I do not like it

      VIP Tester is supposed to get more contribution than normal tester.

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

        No.. VIP tester is the one who follows 1-gon and of course, was a tester. Normal testers are those who still don't follow 1-gon.

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

As a contest tester for the first time :), the contest is great and joyful.

I hope you will enjoy it ;)

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

Someone explain me why the time of this post is showing like 2 days ago ,although it is just posted like 1 hr before i guess

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

It's going to be a great contest :)

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4 months ago, # |
Rev. 4   Vote: I like it +12 Vote: I do not like it

As a trainee of the author i am sure that the problems are epic, Good luck

Give me and my coach contribution :)

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4 months ago, # |
Rev. 2   Vote: I like it +67 Vote: I do not like it

I decided to write the ultimate "as a tester comment" since this is the first and hopefully not the last time to be a tester of an official round (except of course if you count #716 #717).

1) as a tester add me to your friend list

2) as a non-VIP tester I hope I can be a VIP tester one day

3) as a tester I assure you that you should give my friend mo2men contribution

4) as a tester... (recursion ;) )

5) as a tester I advise you to read all the problems

6) as a tester I think you should prepare everything you'd need throughout the round because you won't be able to move or blink during the round

7) as a tester this round is pure awesomeness (kung fu panda 2008 reference)

8) as a tester of this round I would like to test upcoming rounds... maybe the next is yours? who knows

9) as I am 50% of the specialist testers population in this round help me by upvoting this comment

10) as a tester I recommend everyone to eat jilaty (ice cream in Arabic)

Note: the profile picture was taken by my friend and the author Mo2men in the Arab collegiate programming contest 2020 (ACPC)

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

If the problem statements are short, i hope it will be fun to solve!

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

ik this contest is going to be great :-) I'm sure 100%

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

cant be proud more my friends keep going [user:IsaacMoris][user:Uzumaki_Narutoo][user:Blobo2_Blobo2] i sure the contest will be so beautiful ♥♥

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4 months ago, # |
  Vote: I like it +99 Vote: I do not like it

As a tester give me contributions.

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

Error_404, joining this contest cause i found that you are my neighbour xD

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

tdpencil has hacked few of my solutions in the past, so for me he is orZ. yeah!! this orZ has curves.

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4 months ago, # |
  Vote: I like it -26 Vote: I do not like it

MiceMirzayanov is giving me rating in spite of me being lgm this round mark my words uwu

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

keep going!!

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

As a trainee for the author, I am so excited and I am sure that the contest will be amazing as the author is amazing :D

I am waiting for a great contest by a great author :D

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4 months ago, # |
  Vote: I like it +25 Vote: I do not like it

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

تحيا مصر ❤️

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

I can't wait for a great contest <3

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

Wow you really host a div-2 contest when you are just specialist. ORZ

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

    Rating is just a number.

    Also, this man was a problem setter in the Arab collegiate programming contest (ACPC) 2020 and a coach for many CP students, these students are now experts and candidate masters.

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

I just hope I can become a "Pupil" through this competition.

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

    Bro, you are solving 1600 and some 2000+ level problems! you deserve more than that for sure

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

      But I can only solve 2 or 3 problems in Div.2.I am too poor and I am only Grade 6 as a Chinese.

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

      Ahh......I'm too low to solve div.2 .I think I need to do more div.3.(Rank 8000+)

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

        You are in grade 6! I am in my third year of CS degree and still able to solve 3 problems div2... so you are much better off cuz you have so much time at hand! Relax!

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

          Wait,what does "CS" mean?University?Or middle school?

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

            computer science...

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              4 months ago, # ^ |
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              Thank you!But I often call it OI.

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

                No, oi is the short name for "Olympiad in Informatics". CS is computer science which is the name of a major in the university.

                小盆友加油 (ง •_•)ง

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

                  You are also a Chinese?So how many problems should I solve in a normal Codeforces Div.2 if I what to get tg1=?Or I need to solve Div.1?

                  当然,我知道tg1=肯定得等初二左右了...

                  Of course,I know that I should wait for 2 years if I want to get tg1=.

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

                  I start very late you see.. I am still a newbie now.. When I was at your age, I was playing mud back in the school yard and knew nothing about OI. So your age and your time are the most valuable thing. Try to solve more problems. Hope you will be the next WJMZBMR :)

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

                  First,you were a specialist. Second,my mother says that if I can not get >=300 marks in CSP-J and tg2=,she will let me to be a MOer.But the thing I like is program ,not that complex and annoying math.(Maybe I am extreme,but I hope you can understand what I mean.)

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

                  UPD:My highest prize is CSP-J 2= 135 marks,so it is a hard task for me.That's why I want to enhance my strength by CF and Luogu as fast as I can.

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

                  I am going to be Grade 9 now,and I got tg1= last year.You still have long time to study,so I don't think you need to worry about it.I was only a Specialist when I got tg1= :) To the honest,getting a tg2= is not difficult,you can even use brute force to get tg2= easily :)

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

Hope to become "Pupil" through this contest.

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

Good luck to everyone!

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

As you get ready for the contest, I wish you all the best of luck

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

Most valuable advice ❤️❤️

Cap-ture

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

    As a tester ,please orz this guy with a lot of upvotes ,otherwise he is gonna comment frequently for getting upvotes.

    P.S. just kidding but upvote him.i was the 1st to do so :)

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

feels like ages since the last round it's like all problem setters are on a vacation or something

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

This man's rating curve = "The master has failed more times than the beginner has even tried."

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

I really relate with this man's rating....

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

We are so proud of you all , keep going :")

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4 months ago, # |
  Vote: I like it -9 Vote: I do not like it

CKMKB

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

Auto comment: topic has been updated by Mo2men (previous revision, new revision, compare).

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

I will reach pupil in this contest.

Thank You

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

I am so excited to participate in this round, hope everyone will gain rating

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

From the score distribution, it looks like it's going to be speedforces for A, B, C.

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

    Lol maybe for high rated people like you it may seem as speedforces but i don't think that guys like me feel so :).best of luck

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

    I sense more like AB speeforces

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

      I missed the part where that's my problem.:)

      P.S. just kidding bro .i do feel the same bruder ,best of luck

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

      Author revised the score distribution. Previously it said C was 1250 points, that's why I included C as well. Now it looks better.

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

Auto comment: topic has been updated by Mo2men (previous revision, new revision, compare).

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4 months ago, # |
  Vote: I like it -43 Vote: I do not like it

whenever specialist expert makes a contest they always make it hard. If u are actively giving contests u know what I mean. They think it's cooler to make a harder contest. These pathetic nerds cant solve the all question themselves.

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

    Your Comments suit your Name!

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

    Chill mate! No need to be so dramatic. There will always be another contest if you don’t like this one.

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

    He is true. This round is awful. Tests in E are so strong that every wrong solution can pass it :)

    Do they have better ideas?They got a interesting idea(problem E) and some "strong" tests.

    Bad ABCD,real “speedforces”. The worst round I've ever seen.

    Finally,thanks the writers for this "wonderful" round :):):)

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

Short problem statements, thats what we wanted

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

Waiting for a good contest!

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

I always used to think that to increase rating one have to solve more and more problems. Mo2men has solved more than 2000 problems then why his rating is not increasing ( ・᷄ ︵・᷅ )

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4 months ago, # |
  Vote: I like it -59 Vote: I do not like it

i hope i can get top 10 in this contest

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

Oh interactive, is this binary search ? :V

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

    May or may not be, interactive problems need not be always binary search always :)

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

Looks like today their ll be more of a number theory problems.

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

We all are ready for this great contest. Best wishes to all

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

As a participant I wish to gain some precious contribution through this comment.

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

waiting for the contest.

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

تحيا مصر ❤️

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4 months ago, # |
  Vote: I like it -20 Vote: I do not like it

will be unbalanced contest , I can bet

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

hope that a and b will not be interactive

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

Exciting for interactive problem

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4 months ago, # |
  Vote: I like it +45 Vote: I do not like it

Last few days I faced a lot in my life, Can't reveal what exactly happent. But you can assume that the sadness is as same as when you lose your father or mother or see them cry.Couldn't give last 3 contests with proper emotional and mental strength.But skipping a contest has never been an option for me.It's the only thing I have in my life to live for.I will try my best today.Good luck to everyone too

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    4 months ago, # ^ |
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    Good luck bro ull get to specialist today :)

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

    Come on bro! It's only a part of the life. I hope you can come out of the gloom and step into the light as soon as possible.

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

      Yes!!While there is life, there is hope...If the great Stephen Hawkins figured out life even after getting paralysed,Hopefully I can too.

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4 months ago, # |
  Vote: I like it -15 Vote: I do not like it

الله يبلدنا الله ❤️❤️

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

Good Luck Everyone!

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4 months ago, # |
  Vote: I like it -37 Vote: I do not like it

Such boring problems...

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

Is it just me? getting a TLE on tc2 for problem A

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    4 months ago, # ^ |
      Vote: I like it -17 Vote: I do not like it

    Yeah, I got it as well. It's a stupid question. Finally figured out the problem.

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      4 months ago, # ^ |
        Vote: I like it -19 Vote: I do not like it

      My O(n) got tle! Anyway good luck to you for rest of the contest.

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

        My O(n) got Ac.But I'm afraid of getting FST :(

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          4 months ago, # ^ |
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          I got pretests passed first

          then in sys testing I got TLE on test case 2 :|

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    4 months ago, # ^ |
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    Because reading doubles is very slow.

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4 months ago, # |
  Vote: I like it +28 Vote: I do not like it

Remind me when I'm trying to take part in another weird round and get negative delta

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

Formally, let your answer be a, and the jury's answer be b. Your answer is accepted if and only if |a−b|max(1,|b|)≤10−6. How to achieve this in Java ??

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    4 months ago, # ^ |
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    use double, It'll take care of it automatically (if your approach is correct).

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      4 months ago, # ^ |
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      My approach was correct but sadly I used float. Anyone please check my profile using codeforces visualizer and tell me what I am doing wrong. My rating not increasing.

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4 months ago, # |
Rev. 3   Vote: I like it +27 Vote: I do not like it

Why the gap between C and D was a lot ?

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

    toxic:(

    check his original comment

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

    How will you know the balance of the questions if you only solved A?

    Original comment : fuck you with your fucking unbalanced contest

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      4 months ago, # ^ |
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      You can look at the gap of D and C in the standings after system tests :)

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        4 months ago, # ^ |
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        Why even care when you even can't solve B? Your toxicity is full of shit

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4 months ago, # |
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First experience of being able to do B but not A XD.

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4 months ago, # |
  Vote: I like it +64 Vote: I do not like it

giving combinatorics without some relatively big testcase — unethical:/

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4 months ago, # |
  Vote: I like it -126 Vote: I do not like it
ll n;
cin >> n;
ll k;
cin >> k;
vector<ll>arr(n, 0);
for (ll i = 0; i < n; i++) {
    cin >> arr[i];
}
ll sz = 1;
for (ll i = 1; i < n; i++) {
    if (arr[i - 1] > arr[i]) {
        sz++;
    }
}
if (sz <= k) {
    cout << "YES\n";
}
else cout << "NO\n";

why I am getting wa for this..its the correct soln

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

    you are asking this during contest thats what you doing wroong

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4 months ago, # |
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I just erased my whiteboard 5th time full of test-cases for C and yet I am unable to decipher. I am almost sure it's gonna be a one-liner but I just can't figure it out :(

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4 months ago, # |
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I think the gap between the problems is too big :(

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4 months ago, # |
  Vote: I like it -55 Vote: I do not like it

Egypt ki maa ka bhosda

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4 months ago, # |
Rev. 2   Vote: I like it +45 Vote: I do not like it

plz answer me a question whether you like the weak samples just because you think they're cool???

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

    My D is failing pretest 4 though :P

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

      Seeing so bad testcases for C, its impossible to know if the solution is even remotely correct. All my submissions passed the samples and failed pretests.

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

        I wrote a brute-force solution to generate answers for the smaller values. It helped to pass the pretests at least. Let's see whether it passes the system tests or not.

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

        It's not tough to write a brute force solution for C to verify.

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

      Very relatable.

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        4 months ago, # ^ |
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        What did you do to fix it?

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          4 months ago, # ^ |
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          I just added more parameters into my segmentree nodes and it worked. (Previously I used a set to maintain values.)

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

            Wait, like I should compress values with some more like $$$l - 1$$$, $$$l$$$, $$$r$$$ and $$$r + 1$$$ instead of just $$$l$$$ and $$$r$$$? If this is the case I'll be sad for another few days :P

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

              No, I think I did the same thing as what you did, but instead of keeping the max values in the segment tree, I used minimum values, but I have no idea whether your approach is right or wrong, because I iterated through the rows from 1 to n, not n to 1.

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4 months ago, # |
  Vote: I like it +27 Vote: I do not like it

How the hell are 2500 people able to solve C

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

    I'm also wondering this too... So overall I'm too weak...

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

    Telegram I guess

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

    My might fail in sys test, I checked the submissions of the people in my room and all of them have similar code but completely different logic than mine....Hope the pretests are strong

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      4 months ago, # ^ |
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      is C easy ?

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        4 months ago, # ^ |
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        will reply after the contest is over in 2 mins :D

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

        I tried the following but probably got stuck in some ridiculous edge case.

        for ith bit, the no of elements in the array with ith bit set should either be >= 2 or 0.

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

        Its decent.... combinatorics and inclusion exclusion.. 1600 I guess

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

    I think about this issue like this :

    Consider sequentially from the high binary bits to the low binary bits.

    The i-th binary bit can be "decided" or "undecided".

    Decided means that the i-th binary digit a1 & ... an is already greater than a1 xor ... an, and no subsequent comparison is required at this time.

    Undecided means that the value of a1 & ... an and a1 xor ... an can be compared after the i-th binary digit.

    Undecided includes two situations : - n numbers are all 1 in the i-th binary digit and n is an odd number. - At least one of the n numbers in the i-th binary digit is 0 and there is an even number of 0s.

    Undecided means that all n numbers on the i-th binary bit are all 1 and n is an even number.

    The final answer is composed like this :

    • Undecided Decided Random
    • Undecided

    my code like this

    # include <bits/stdc++.h>
    # define int long long
    using namespace std;
    const int mo=1e9+7;
    int pow(int x,int n){
    	int ans=1;
    	while (n) {
    		if (n&1) ans=ans*x%mo;
    		x=x*x%mo;
    		n>>=1;
    	}
    	return ans;
    }
    signed main() {
    	int t; scanf("%lld",&t);
    	while (t--) {
    		int n,k; scanf("%lld%lld",&n,&k);
    		int res=pow(2ll,n-1);
    		if (n&1) res=res+1; else res=res-1;
    		int ans=pow(res,k);
    		if (!(n&1)) {
    			for (int i=1;i<=k;i++) {
    				ans=(ans+pow(res,i-1)*pow(pow(2ll,n),k-i)%mo)%mo;
    			}
    		}
    		printf("%lld\n",ans);	
    	}
    	return 0;
     } 
    
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4 months ago, # |
  Vote: I like it 0 Vote: I do not like it

shitty problems, bad balance and there are only 5 problems AT ALL

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

How to solve C?

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

Am I the only one here who had 2 penalties because of ignoring the fact that $$$-10^9 \le A_i \le 10^9$$$

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

    I got soo many wrong answers on B because a[i] can be 0. Why they didn't make a[i] permutation of length n? Anyway, I think that problems were ok but samples and these constraints were horrible.

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

      I had the exact same issue, I got first WA because $$$A_i$$$ can be 0 and 2nd WA because $$$A_i$$$ can be -1

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

    Probably not, but I'm pretty sure I'm the only one who submitted with the wrong language settings on two different problems (ugh).

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

Weak sample for C :(

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

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

In div2 B i was rearranging the elements inside subarray for half an hour.

Sad noises.

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4 months ago, # |
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I liked B it wasn't clear why the simple solution is not working but C is so hard still a good problem though I will try to solve it later

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    4 months ago, # ^ |
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    Why did the simple solution not working in B?

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

      1 3 2 <- try this test case

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

      consider this case

      4 2
      2 3 5 4

      simple solution output Yes but it's a No cause you need k=3 you can't put 4 in middle 2 3 5

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

        I compressed elements to 0 to n-1 and checked if a[i] — a[i-1] == 1.

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

Is there another way to solve problem D instead of using a dynamic segmentree, curious -.-.

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

    As long as the queries are not online, you can (almost) always use coordinate compression and use a normal segment tree.

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

      Can you share your code pls. Your all submissions are still locked :(

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

UPD: my bug was that I had to declare the Segment Tree Array with 8n elements

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4 months ago, # |
Rev. 2   Vote: I like it +7 Vote: I do not like it

Contrary to popular belief, I liked problem C. A good question based on bit contribution and combinatorics.

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

    Even though I couldn't solve it but it indeed feels like a good problem. I hope to learn something great from the problem

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

So i had this idea and observation for problem C:

For every number >= 1 times that it occures must be even. For example: 02211, 02222, 22110 etc. Total number of possibilities that pair of numbers can occur is n*(n-1)/2. There can be n/2 pairs of numbers in array, so total number of posibilities for 1 number is n*(n-1)/2 * n/2. Multiply this by amount of numbers: (2^k) — 1 * (n*(n-1)/2 * n/2). There also can be n same numbers that make problem condition true. So i also add 2^k to answer.

Can someone told me if that make any sense :D? Thought that would work but it didn't :/. Maybe it was only right for small numbers dunno

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

    Misses cases like [1,2,3] e.g total xor = 0 total and = 0. Also misses the idea if n is even you can set the leading bit to 1 in all values and set all other bits to any values.

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

Interesting problems. Is D a segment-tree problem? I think I could solve it if only I could implement a generic segment tree.

and btw. why a * b % c == (a * b) % c and a + b % c != (a + b) % c :<

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

How to solve problem D . I think it is similar to longest increasing subsequence problem in a way $$$a[j]>a[i]$$$ if $$$j>i$$$ and $$$ j^{th}$$$ row and $$$i^{th}$$$ row have some common intersection . I tried to use segment tree but could'nt implement in time

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

Very clever to do tests with k = 1 and k = 0 on a combinatoric problem! Good job!!! Don't do any other contests please.

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

Why in problem A a hack with: t = 1,n = 10^5 and all a[i] = 10^9 gives invalid input?

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4 months ago, # |
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I spend about 1 hour on D......the solution is easy but it's hard to code :(

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4 months ago, # |
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How to solve D any hints? do we construct some kind of graph?

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    4 months ago, # ^ |
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    use dp

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

    Segment tree with DP is what I did. First compress all intervals, so that we can fit a normal segment tree in. Let $$$dp_i$$$ be the minimum number of rows we have to remove to make rows $$$1~i$$$ good, and keeping the i_th row. Then the dp recurrence is pretty simple: $$$dp_i = min(dp_j)+i-j-1$$$, where (j<i). We can rearrange the formula into $$$dp_i-i=dp_j-j-1$$$ then we can keep the value $$$f_i = dp_i -i$$$ in the segment tree. For the segment tree, we update the ranges of ones of that specific row with $$$f_i$$$ and for the queries to check the previous rows for the dp recurrence, we also query only the ranges where ones are located in the i_th row.

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

I think the examples of the problems are so easy that it makes me be not able to find the bugs.

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

I just loved $$$E$$$. Nice puzzle. Here's a small hint for those interested:

Hint
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    4 months ago, # ^ |
      Vote: I like it +19 Vote: I do not like it

    Okay, as the editorial solution is entirely different, I will describe my solution here (which I liked better).

    Solution

    Code: 125400662

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4 months ago, # |
  Vote: I like it +3 Vote: I do not like it
Solution for D
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    4 months ago, # ^ |
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    I’m getting WA on Test Case 4 with this approach :(

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      4 months ago, # ^ |
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      Yeah, I also got that first but I found the bug in my implementation and corrected it.

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

My solution on E seemed to read a direction other than the ones described in pretest 3. It's likely I got a bug somewhere, but did anyone notice any similar weird behavior, because I can't seem figure it out?

Edit: Found a bug and got AC, still not sure what my program managed to read after producing a wrong move.

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

Soooo weak server System!!!

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

How to solve C?

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    4 months ago, # ^ |
    Rev. 2   Vote: I like it 0 Vote: I do not like it
    Spoiler
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4 months ago, # |
Rev. 3   Vote: I like it 0 Vote: I do not like it

How to solve problem C?

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4 months ago, # |
  Vote: I like it +28 Vote: I do not like it

Your example is so stronger that every wrong code can pass!

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

What is the problem with MLE pretest 4 in Problem D? Was I the only one to struggle with this?

I used a lazy segment tree to build a graph then found the longest path in an acyclic graph. You only need to add an edge to the nearest row that intersects with your current interval. Is that approach wrong or what?

Edit: NVM, FeelsBadMan

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

Got TLE on C because of 32-bit python.

Very annoying.

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

why you bully me , codeforce ?

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4 months ago, # |
Rev. 4   Vote: I like it +169 Vote: I do not like it

What the fuck? I randomly submitted this pattern in E and it passed pretests.

(Edit : It passed system test)

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    4 months ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    This solution made me feel disappointed :(

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

    And now you will become CM XD. Congrats

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    4 months ago, # ^ |
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    and now it's Accepted. wtf

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      4 months ago, # ^ |
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      This might be somehow the solution..? Main test had 7000 individual games and it all worked.

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

        Nope. It's wrong. It's just hard to make an opponent to counter all such solutions I guess.

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

          Maybe because the opponent isnt an AI that makes its move optimally, but instead it makes its move randomly so the probability will be so low to fail?

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

        I really really dont think so because when you are on (2,1) and go to (3,1) i can be on (3,6) then move to (2,6) and then to (1,x) and its over. (1,1) is the point in the upper left corner.

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

    And it turns out to be AC in main test.

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

    I can think of a test case where this solution doesn't work. The system tests are weak.

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    4 months ago, # ^ |
    Rev. 3   Vote: I like it +76 Vote: I do not like it

    If the gif doesn't work, go to here

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

    I just continue to go in reverse path and it passed main tests. Indeed the solution above fails only last test.

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

Nice round guys, I enjoyed the problems :D

AhmedEzzatG Mo2men

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

How to solve C? It looked like a DP-Tabulation type of problem, but all I could figure out is that

$$$dp[n][k]=(2^{n-1}+1)^k$$$ when $$$n$$$ is $$$odd$$$

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

    Let $$$p = 2^{n-1}$$$. Then the answer is

    $$$\begin{cases} (p+1)^k & n\ \textrm{odd} \newline \dfrac{\left(2p\right)^k+p\cdot\left(\frac p2\right)^k}{p+1} & n\ \textrm{even} \end{cases}$$$

    How I got it:

    I brute-forced many small values (my brute force was $$$O(n2^{nk})$$$ and worked well enough for $$$n+k \leq 12$$$ (took only 80 seconds with pypy!). I immediately noticed the powers of $$$5$$$ and $$$17$$$, and checked for $$$65$$$ and $$$257$$$. For the evens, I noticed that $$$\textrm{ans}(2,k) = 3\cdot\textrm{ans}(2,k-1)-2$$$. I plugged this into Wolfram Alpha and got that it was $$$\frac{4^k+2}3$$$. Then, I tried brute forcing expressions in the form $$$\frac{a^k+b}c$$$ for $$$n = 4$$$, but found nothing. Then I tried changing the expression for $$$n=2$$$ to $$$\frac{4^k+2\cdot1^k}3$$$, and checked that form of expressions, and got $$$\textrm{ans}(4,k) = \frac{16^k + 8\cdot7^k}9$$$. From there I generalized it.

    The modular exponentiation makes the time complexity $$$O(\log n + \log k)$$$.

    Also, looking at submissions of random people, I've seen at least 4 different solutions other than mine (though they're all about $$$O(n+k)$$$, so mine is faster), so there are many ways to solve this problem.

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

    even is $$$\frac{\left(2^n\right)^k-\left(2^{n-1}-1\right)^k}{2^{n-1}+1}+\left(2^{n-1}-1\right)^k$$$.

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

    Video solution, you can also convert the recurrence into a 1D DP (DP solution).

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

I'll probably fall to Specialist, but I really loved this round! Problem C was interesting, bit-manipulation and combinatorics puzzled me oh so good.

Kudos to the entire problem-setting team!

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

Can C be solved using DP?

I tried to implement via a 4-D dp dp[i][_and][_xor][eq].

At the ith bit (out of k), I have 4 ways of assigning bit combinations to the _and and _xor values -> 0 0, 0 1, 1 0, 1 1, and eq can be 0/1/2, denoting whether the & cumulative value until the ith bit is lesser, equal or greater than that of the ^ cumulative value. Couldn't implement the combinatorics part for each of the combinations in time. But, would this solution work?

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

    Clean dp:

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

      not sure what I have done dp:

      ugly dp
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    4 months ago, # ^ |
    Rev. 3   Vote: I like it 0 Vote: I do not like it

    Count cEven the number of ways to pick an even number of 1's in an n-bit number. Then do dp on the most significant digits: if n is odd you have dp[i] = dp[i-1]*(cEven+1) (+1 is the case of all digits being ones). The second term is the number of ways the first digits can be equal. If n is odd then dp[i] = dp[i-1]*(cEven-1) + 2^(n*(i-1)). Here the second summand is the case of the first digit of the AND being larger than that of the XOR so any combination of digits other than the first works. The first summand is the digits being equals (you remove 1 because if all digits are 1 then there are an even number of them but then the AND term is larger). You can precompute the powers of 2 mod M as n is always the same.

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4 months ago, # |
Rev. 2   Vote: I like it -14 Vote: I do not like it

great contest

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

    k = 0 should always be 1 independent of n. I think it's more about them screwing with you and putting k = 0 as a valid test case at all than anything else

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4 months ago, # |
  Vote: I like it +35 Vote: I do not like it

Well, it seems there is some disrespectful comments. Please respect the setter. For me C was good problem, and although I couldn't solve, E was also interesting. Thanks for the contest.

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4 months ago, # |
  Vote: I like it -28 Vote: I do not like it

Author Mo2men struggles to solve div2 C so he make others to struggle .

He may have won but at what cost.

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

one of the most balanced div 2s ever. Kudos to the authors !!

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4 months ago, # |
Rev. 4   Vote: I like it +25 Vote: I do not like it

I thought constraints to be different for C, so I solved it for $$$T <= 10^5$$$.

Solution
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4 months ago, # |
  Vote: I like it -45 Vote: I do not like it

This is why i am against rounds created by specialists/experts or low CMs they only try to make the contest hard.

Overall view -> No original idea.

A -> good for div2 A B -> shitty observation problem/ also you could have made statements clear. C -> shitty Combinatorics problem with simple cases one can do it. D -> No comments E -> No comments

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

I wrote a solution of C but it was giving wrong answer on test case 2. Can someone explain what is wrong with the logic. I used 1-d dp. dp[0]=1 and for i from 1 to k - When n is even, dp[i]=2^(n*(k-1))+(2^(n-1)-1)*dp[i-1] - when n is odd, dp[i]=(2^(n-1)+1)*dp[i-1]. here is the link to my code

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    4 months ago, # ^ |
    Rev. 3   Vote: I like it +1 Vote: I do not like it

    Here's my code full code: https://codeforces.com/contest/1557/submission/125410342

     int even(int n,int k){
         if(k==0)return 1;
        return  mod_add(modpow(modpow(2,k-1),n), (modpow(2,n-1)-1)*even(n,k-1));
    }
    
    int odd(int n,int k){
         return modpow( modpow(2,n-1)+1,k); 
    }
    
    void solve(){
    
        int n,k;
        cin>>n>>k;
    
        if(n%2==0)cout<<even(n,k)<<endl;
        else cout<<odd(n,k)<<endl;
    
    }
    
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      4 months ago, # ^ |
      Rev. 2   Vote: I like it 0 Vote: I do not like it

      wth man. I think my code is exactly same as yours. You just used recursion and I used loop then why on earth it is giving me wrong answer!!!!

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

      Could you elaborate on your logic?

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

        You need to consider 2 cases.

        if n is even:

        if we are the kth bit we have 2 options

        • Either we put bits in such order that 'and of the kth bit =1 and xor=0. For this bits at the kth position of all numbers needs to be 1 and the rest for (0- k-1) bits we can put any sequence of bits that will be equal to modpow(modpow(2,k-1),n).

        • or, we put bits such that 'and' and 'xor' both are equal for that (number of 1 bit == no of 0 bits) or all bits ==0 and then recursively call for (n,k-1)

        if n is odd:

        • We can only make a1&a2&a3==a1^a2^a3. Just number of set bits needs to be even
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4 months ago, # |
  Vote: I like it +10 Vote: I do not like it

Nice round and keep going, guys :) It is sad to tell nowadays that many CF members don't like any problems, neither easy nor hard. They only like complaining and staying in comfort zone.

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    4 months ago, # ^ |
    Rev. 3   Vote: I like it -76 Vote: I do not like it

    I just want to know HOW MUCH dollars did you get from these writes?

    I don't think a man can say these words after participating. How dare you to comment these f...ing words without your brain. :)

    If I can earn dollars by posting comments like you,please tell me. :)

    Finally, I wish the author and you a long life, a happy family and good health. Thanks a lot :) :) :)

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

      May you get the most downvotes anyone has ever received!

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        4 months ago, # ^ |
        Rev. 2   Vote: I like it +9 Vote: I do not like it

        Thank you :) I just want to earn money like you guys :(

        If they aren't able to write a contest,please go to problemset and practise more,rather than giving us five naive problems. :)

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

          you are a div1 alt....go and participate in div1 if u have balls

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

            I have participated in div1.... But it has nothing to do with "div1". Anyway,this round is awful.

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          12 days ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Having participated myself I want to say that this round’s truly not-so-good. Have myself puzzled throughout the contest.

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

    Tell me,why do you think this round is nice?Say a reason rather than hurrying downvoting me.

    Or you guys just want a interesting problem that you can accpet by printf("rand()") ,or four problem that has been written years ago?

    Why do you lovely guys participate a codefoces round?To solve five cute naive problems and get nothing?:)

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

One good thing about this contest is that I didn't face any lag today. The system was pretty smooth for me. The difficulty level of problem D was a bit on the hard side than a regular Div-2 D, to be honest. Overall, had a good time brainstorming. Thanks Mo2men & AhmedEzzatG for the contest.

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

What is the answer for this input in problem C: n= 1, k = 0. In my Accepted submission, it is 1. But I saw an accepted submission where it is 0.

https://codeforces.com/contest/1557/submission/125390194

I guess the setter didn't include this test in the system test.

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

Why the verdict of my submission is still Pretests passed? Problem B