Nickolas's blog

April Fools Day Contest 2020
By Nickolas, 5 years ago, translation, In English

The contest is over; I hope you enjoyed it! The editorial is available here.

The 8th April Fools Day Contest will take place on Wednesday April 1st. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018, 2019.

As usual, to enjoy competing in this round you'll need a sense of humor compatible with mine. Good luck, and have fun!

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  • Vote: I do not like it

Comments Comments (239)
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5 years ago, # |
  Vote: I like it +104 Vote: I do not like it

This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

It's the extreme of those hard-to-comprehend problem statements.

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

Will the editorials be posted ?

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    5 years ago, # ^ |
      Vote: I like it +57 Vote: I do not like it

    Not before the contest :-) You can see that all past contests have editorials.

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    5 years ago, # ^ |
      Vote: I like it +257 Vote: I do not like it

    You better ask will there be problem statements

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    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +59 Vote: I do not like it

    1st Plot twist:Contest cancelled

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      5 years ago, # ^ |
        Vote: I like it +275 Vote: I do not like it

      Plot Twist 2: Contest is rated

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

        Plot Twist 3: Contest will take place on April 2nd

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          5 years ago, # ^ |
            Vote: I like it +43 Vote: I do not like it

          Plot Twist 4: Contest will start two hours in advance.

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            5 years ago, # ^ |
              Vote: I like it +138 Vote: I do not like it

            Plot Twist 5: Final standing will be the reverse of actual one.

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

              Plot Twist 6: No time penalties on Wrong Submissions! xD

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                5 years ago, # ^ |
                ← Rev. 2   Vote: I like it +50 Vote: I do not like it

                Plot Twist 7 : When we think there's a plot twist hidden but turns out there is no plot twist at all

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                  5 years ago, # ^ |
                  ← Rev. 2   Vote: I like it +22 Vote: I do not like it

                  Plot Twist 8: contest will be onsite.

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

                  Plot Twist 9: codeforces goes for maintainence during contest time.

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                  5 years ago, # ^ |
                  ← Rev. 3   Vote: I like it -56 Vote: I do not like it

                  Plot Twist 10: We will be competing while living in artificial reality.

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                  5 years ago, # ^ |
                    Vote: I like it -60 Vote: I do not like it

                  Plot Twist 11: It's last plot twist

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                  5 years ago, # ^ |
                    Vote: I like it +85 Vote: I do not like it

                  Plot Twist 12: Plot Twist 11 was intentionally misleading.

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

                  Plot twist 13: This is not a plot twist.

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                  5 years ago, # ^ |
                    Vote: I like it +33 Vote: I do not like it

                  Plot Twist 14: There is no plot.

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

                  Plot Twist 15: There is no twist.

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                  5 years ago, # ^ |
                    Vote: I like it +73 Vote: I do not like it

                  Plot Twist 16: Only language allowed is BrainFuck.

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

                  Plot Twist 17: 17 is equal to 0

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

                  Plot Twist 18: The contest will be cancelled.

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

                  ... and that's how we know that plot twists are periodic with the period of 17! (Well, assuming that each next plot twist is a function of exactly one plot twist immediately preceding it)

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                  5 years ago, # ^ |
                    Vote: I like it -23 Vote: I do not like it

                  Plot Twist 17 + 2: Contest is rated

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                  5 years ago, # ^ |
                    Vote: I like it -18 Vote: I do not like it

                  Plot Twist 17 + 3: Contest will take place on April 2nd

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

                  Plot Twist 17 + 4: Contest will start two hours in advance.

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

                  Plot Twist 17 + 5: The problem statements will be locked and can only be accessed after you submit and lock the solution.

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

                  Plot Twist 17^6: Only output is provided and you have to find problem statement with input.

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

                  Plot Untwist 17 + 7: this will untwist all the twists without further twisting already twisted plot.

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

                  Plot Twist 25: The contest is running.

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

                  Plot twist:

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

                  Plot Twist 27: Actually ,its not 27th but 28th twist(count it).

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

                  Plot Twist 29: pilot is going to die.

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

                  Plot twist 10^9- Plot twist Time Limit Exceeded!

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

                  Plot Twist 10^9+7 "RunTime Error"

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

                  The Plot Twist we expected : Everything above

                  The Plot Twist we got : Error 502 Bad Gateway across all versions of the website !

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

                  plot twist 10: gets a "f***"in judgement protocol.

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

                  Plot Twist 34: Those commenting on this thread will have their rating increased

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

    (Assuming its April Fools Day)
    Yes!! before the contest!!

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5 years ago, # |
  Vote: I like it +51 Vote: I do not like it

Pretty much every recent contest has started to feel like a joke contest now, so this joke contest is more like just another normal contest. So I don't see why it should be unrated.

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

I think this is going to be fun :D

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

It's my first April Fools Contest in Codeforces. I think it'll be interesting and meaningful (to me). Just wish me (and everyone) good luck and have fun!

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5 years ago, # |
  Vote: I like it +33 Vote: I do not like it

What if you don’t have a sense of humor?

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    5 years ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    Then it falls to other people to make fun of you.

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5 years ago, # |
  Vote: I like it +35 Vote: I do not like it

April Fool's joke:

Us: Yes!!, unrated contest.

CodeForces: April Fool's, it's rated.

Us: rating drops

CodeForces: Just kidding... :P

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

Seems interesting, very much looking forward to it.

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

Excited for the contest in this QUARANTINE...

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5 years ago, # |
  Vote: I like it +95 Vote: I do not like it

Is it fair to call the winner a fool ?

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5 years ago, # |
  Vote: I like it -30 Vote: I do not like it

Why it will be unrated ?

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

    Have a look on previous year contests, you will get to know.

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

plot twist : contest will be rated Nickolas is a paid actor

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5 years ago, # |
  Vote: I like it +35 Vote: I do not like it

Waiting for another one OEIS task.

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

    Which is why I can't really give one :-D I'm not sure this is a kind of joke that gets better after multiple repetitions, and you can pull off a trick like this only once :-)

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

Will each problems have the same points? What will be the difficulty level of each problem? Same or Different?

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

    ACM ICPC rules mean that each problem is worth 1 point regardless of complexity, and the ties are resolved using penalty time. The problems will have different difficulty; I try to arrange them in increasing order of difficulty but for this kind of contest it's harder than usual to estimate this correctly :-)

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

I hope there are no problems with solutions based on references specific to the problem setter of the contest. (like this one — https://codeforces.net/contest/1145/problem/C)

I think the problems should be solve-able for all users irrespective of whether they follow specific other users or not. Science/math trivia and general movie/pop-culture references are fine, and would allow a greater number of users to attempt the problems.

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

    Yes i agree with you

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

    I solved that problem during contest without knowing the reference to problem setter or anything about quantum computing.

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

    actually this is a very good point

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

This quarantine it feels good to be fooled.At least something is happening.

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

One of the best chances to rank over reds :p

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

I'm waiting for the memes based on the disasters happened in 2020 so far

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

One of the most funniest contests.

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5 years ago, # |
  Vote: I like it +35 Vote: I do not like it

your wish of "short statement" will be fulfilled here.. for sure!

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

Hoping for a mind refreshing and entertaining contest with a lot of humorous content in this Quarantine Times!!!

PS: For the first time I am going to give a contest with my family!!

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

Boys often don't understand the humor in girls. Then What?

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

    I don't think the issues people usually have with April Fools Contests are related to my gender... But in this unlikely case, you still have two problems written by my co-author kit1980 :-)

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

If "unrated" is a joke XD

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

No April Fools Day Contest in 2015?????

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

When someone tells you after the contest that has been rated.

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

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5 years ago, # |
  Vote: I like it -37 Vote: I do not like it

BREAKING NEWS: AtCoder and CodeForces are now working together and will share the system as of today.

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

I hope those problems don't make me go bald hahaha

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5 years ago, # |
← Rev. 2   Vote: I like it +34 Vote: I do not like it

Le output format : The correct spelling for school is school, if you put the second 'o' before the first 'o' it is absolutely wrong.

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

There will be no contest...It’s all a joke and I’m not gonna fall for it.

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

We need a round based on dank memes.

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

lets post all the solutions here after getting AC :D

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

Can I participate with my team?__

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

Latest News = Competitive Programming is going to be introduced in this Summer Olympics ... Congrats to Whole Coderforces Community for this tremendous achievement :-) .

https://www.nytimes.com/newsletters/computerscience/1087

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

It is April Fools Day Contest, right? Will the problems be fool, or are they gonna make us feel like a fool? Which one do you think?

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

Its april fools day and CodeForces is kindda joking with me (note to the Memory).thank u CF for making us to smile while we quarantine ourselves.

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5 years ago, # |
  Vote: I like it -23 Vote: I do not like it

Is contest rated?

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

Theres no questions. Was that the joke ?

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

problem is not showing up just input and output for every problem and i entered in it i don't know now what to do

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5 years ago, # |
← Rev. 2   Vote: I like it +15 Vote: I do not like it

 

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

I was thinking in which categories does these question falls ?

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

hope all contests have problem statement concise like this one

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

Is it rated? Can someone hint over this?

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5 years ago, # |
← Rev. 3   Vote: I like it -10 Vote: I do not like it

NULL

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

Multum gaudebamus fuit!

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5 years ago, # |
  Vote: I like it +59 Vote: I do not like it

tourist got the 1st like usual even though this is just a joke round, insane!

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5 years ago, # |
  Vote: I like it +101 Vote: I do not like it

How on earth is tourist first in this contest too

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

Never have I been so curious to know the solutions. Can't sleep without the editorial.

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5 years ago, # |
  Vote: I like it +79 Vote: I do not like it

tourist: Rated, unrated; I am inevitable.

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

Everyone who attempted A got it correct, this the first time that I have seen it happen.

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

    I print nothing and got WA at first...

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

    There is only 1 test, and WAs on the 1st test are not shown as failed attempts. Trust me, not everybody got it from the 1st try :-D

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

    Not Me , It took me my third attempt;

    On my first attempt i read

    input -standard input output-standard output ,so i took a input number and printed that number.

    Later ,i submitted my blank template in my second attempt;

    And finally printed NO after that..

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

      I meant got it correct during contest not on first attempt :)

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5 years ago, # |
← Rev. 2   Vote: I like it +25 Vote: I do not like it

I had to check from tourist's submissions page, to check whether he actually submitted the problems, or we were being fooled by CF. LOL! xD

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

    What if his submission page is also made up? What if he never really attended the contest?

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

SOLUTION FOR E

First: fill area in photoshop

Second: Do 2d dimension arr. Check pixel at (i*15)+5 (g*15)+5. If it's white, put 0 in arr else put 1; Save that arr in file for use it in final solution. I picked Node.JS for this step.

var fs = require("fs");
var Canvas = require("canvas");

let fileLink = "smile.png";
var canvas = new Canvas.Canvas(960, 960, "png");
var ctx = canvas.getContext("2d");

const Image = Canvas.Image;
var image = new Image(963,964);
dataArr = [];
image.onload = function () {
    ctx.drawImage(image,-2,-2,963,964);
    for (let i = 0; i < 64; i++){
        let newStr = [];
        for (let g = 0; g < 64; g++){
            var p = ctx.getImageData((g*15)+4, (i*15)+4, 1, 1).data;
            if (p[2] < 240){
                newStr.push(0)
            } else {
                newStr.push(1)
            }
        }
        dataArr.push(newStr)
    }
    fs.writeFileSync("DATAOUT.txt",JSON.stringify(dataArr))
};

image.src = fileLink;

Final solution: just get row and col and check arr[row][col] if it's 0 print "OUT" else print "IN"

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

    mspaint.exe FTW

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      5 years ago, # ^ |
        Vote: I like it +39 Vote: I do not like it

      when your linux distro does not package a drawing tool so you search 'online image editor' and pick the first one with a floodfill tool

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

    Or you can use this

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

    GIMP supports an excellent image format: it can export images as C code (the code for a struct with the raw uncompressed bytes stored in a unsigned char[] field). I used that.

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    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +10 Vote: I do not like it

    Another solution without calculating coordinates. Fill area with black, resize to 64x64 and just convert pixels in python to C++ format:

    import imageio
import numpy as np
ans = np.array(imageio.imread("maze.png"))[:, :, 0]
for line in ans:
    print('{', end='')
    print(*map(lambda x: 1 if x == 255 else 0, line), sep=',', end='')
    print('},\n', end='')
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5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

When will we receive the editorials? :P

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

How do I solve F?

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

    "elementary" -> periodic table of elements. Check if word can be spelled using symbols of chemical elements.

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

H is awful and awesome at same time

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

    How to solve?

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

      code in ArnoldC

      Solution
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      5 years ago, # ^ |
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      code
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5 years ago, # |
  Vote: I like it +48 Vote: I do not like it

How to solve I?

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

First (and for sure last) time I solved 7 problems lol.

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

)

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

What are the solutions?

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5 years ago, # |
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How to solve F?

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

Was this part of April fool's suprise? I couldn't even find the submit button XDD

// For some moment I REALLY thought it was some kind of penalty for submitting too many WAs

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

Having a picture with coordinates may help you solve E problem （做了一张有坐标的图片，可能会帮助你解答E题）

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

I am stupid, how to solve C?

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    5 years ago, # ^ |
      Vote: I like it +24 Vote: I do not like it

    Paste the title into Google. Google tells you that correct order of these words is in fact a bit different and you can get some permutation from it. You need to apply that permutation to bits of the number on input.

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

      Actually, it's possible to deduce this permutation just from the samples...

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

        Maybe it is, but how do you get the idea behind it then?

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          5 years ago, # ^ |
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          Maybe I wasn't clear enough — the idea was from the title; I'm talking about the permutation itself, the samples give exactly enough information to decode it :)

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          5 years ago, # ^ |
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          The $$$0 \le n < 64$$$ part clearly shows it's an array of bits. Then I noticed the count of 1 and 0 bits in the original number matches the count of 1s and 0s in the result (respectively); then I tried to apply a simple shift. When it didn't work, I just noticed the highest and the 2nd bit don't change and the others are just reversed.

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        5 years ago, # ^ |
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        It is not, no sample contains the terms 2^3 and 2^4, so the mapping of those bits is ambiguous.

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

    And after happily lived ever they
    And they lived happily ever after

    All of the numbers have <= than 6 bits, so reorder the bits just like those words.

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5 years ago, # |
← Rev. 4   Vote: I like it +63 Vote: I do not like it

A — print No.

B — the first letters of each line spell "two factors" (finding the first nontrivial factor x, then outputing x and a/x worked for me).

C — the problem title is "and they lived happily ever after" permuted. Permute the bits in the binary representation of the number, in the same way.

D — is the hexadecimal number even or odd?

E — the problem asks for whether a square is inside or outside the curve. Use a photo processing tool such as GIMP that allows export of pictures to C code, after applying a paint bucket tool.

F — Check whether string can be broken down into chemical element symbols.

G — The language is http://users.monash.edu/~damian/papers/HTML/Perligata.html (unfortunately the link does not seem to contain enough information...)

H — The language is https://github.com/lhartikk/ArnoldC.

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

    For G you can translate the code without any resources, it just takes a bit.

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      5 years ago, # ^ |
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      I have no idea how you do that

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        5 years ago, # ^ |
          Vote: I like it +34 Vote: I do not like it

        That's what I did, took about 20mins. You look at it as a linguistic problem.

        You mostly ignore -um, -mentum and -o suffixes because they seem to be just 'latinizing' the text. Then stuff like addementum or multiplicamentum are easy operations.

        Things like "var", "aresult", "bresult", "result" are seemingly just variables.

        Convert all numbers from Roman to decimal to better understand the conditional and loops.

        The order of input-output (reversed) points to the siqus lines likely being pushing/popping in a stack and input is probably in the first loop. The cumula on these lines also points in that direction as "accumulation" points to some data structure.

        The only thing left is to figure out elevamentum and privamentum fodementum. Looking at how big the values are compared to the input and associating with "elevate", the former is a power function.

        Calculating all other values and comparing with the output gives you that privamentum fodementum has to be a square root and you're done.

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        5 years ago, # ^ |
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        I did it without realizing it was an esolang, it's easier than it sounds. For example "aresultum tum bresultum addementum da resulto." clearly means "add aresult and bresult to get result". "multiplicamentum" is also very obvious.

        Most of the lines have very obvious parsings if you think they must be program instructions.

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          5 years ago, # ^ |
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          I think that is because Portuguese (this is your native language, right?) may be much closer to Latin, than English.

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    5 years ago, # ^ |
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    You can add use Lingua::Romana::Perligata "convert"; before the code to make Perl convert the code to an understandable form.

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

GET TO THE CHOPPER!

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

Guys, leave pictures alone, do old school.

10 years ago this was called art!
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    5 years ago, # ^ |
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    looks better like this
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5 years ago, # |
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it was nice experience , saw new perspective of solving a question . I can't find solution for C ..but still enjoyed it

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5 years ago, # |
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Unknown language = Brainfuck?

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5 years ago, # |
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tourist got fooled by A :)

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5 years ago, # |
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Codeforces, is it bug or joke? Why couldn't I to submit problem O?

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

When I find out at the end of the contest I mistakenly got a CE by writing the correct C++ solution of G using UnknownX......

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

Problem F: https://csacademy.com/contest/ieeextreme-practice-old/task/c787255968c972c653677a52599ecc2f/

It seems to me that there is a notorious coincidence......

Also mfw I solved this task back then but didn't solve it now because I thought some of the elements aren't elements cries

I even had a file named Elementary.cpp and I was asked if I wanted to replace that file.......

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5 years ago, # |
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In problem D, I actually did a research on OEIS. Found out that all the sample input were chess related, I thought that the problem is to collect the first element of each chess related sequences. I searched OEIS "chess", got 61 pages, with 607 results. So I wrote a program that collects the data from those pages, and writes the code for me. After I done that, I happily submitted the code and got WA on test 5. And only after all of these, I figured out what the actual task is. I really got fooled.

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5 years ago, # |
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Could not do. I am a fool indeed.

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5 years ago, # |
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never been so stressed.

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5 years ago, # |
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contest get over

solution to last question

IT'S SHOWTIME

HEY CHRISTMAS TREE varX

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YOU SET US UP 0

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GET YOUR ASS TO MARS varX

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DO IT NOW

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I WANT TO ASK YOU A BUNCH OF QUESTIONS AND I WANT TO HAVE THEM ANSWERED IMMEDIATELY

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HEY CHRISTMAS TREE a

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YOU SET US UP varX

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GET TO THE CHOPPER a

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HERE IS MY INVITATION varX

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HE HAD TO SPLIT 1000

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ENOUGH TALK

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HEY CHRISTMAS TREE b

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YOU SET US UP varX

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GET TO THE CHOPPER b

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HERE IS MY INVITATION varX

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I LET HIM GO 1000

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ENOUGH TALK

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HEY CHRISTMAS TREE result

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YOU SET US UP 1

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HEY CHRISTMAS TREE isTrue

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YOU SET US UP 1

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STICK AROUND isTrue

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GET TO THE CHOPPER result

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HERE IS MY INVITATION result

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YOU'RE FIRED a

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ENOUGH TALK

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GET TO THE CHOPPER a

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HERE IS MY INVITATION a

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GET DOWN 2

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ENOUGH TALK

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GET TO THE CHOPPER result

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HERE IS MY INVITATION result

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I LET HIM GO b

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ENOUGH TALK

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GET TO THE CHOPPER isTrue

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HERE IS MY INVITATION a

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LET OFF SOME STEAM BENNET 1

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ENOUGH TALK

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CHILL

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TALK TO THE HAND result

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YOU HAVE BEEN TERMINATED

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    5 years ago, # ^ |
      Vote: I like it +34 Vote: I do not like it

    Please use "```" to format the code, like this:

     ```
 code goes here
 ```
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      5 years ago, # ^ |
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      this might help

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        5 years ago, # ^ |
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        You don't have to put "----" between the lines, you can just type like this:

         ```
 line 1
 line 2
 line ...
 ```
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5 years ago, # |
  Vote: I like it +65 Vote: I do not like it

The problems were extremely nice this time, thanks!

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

Fun contest :)

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5 years ago, # |
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Is the contest is rated?

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5 years ago, # |
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Was problem G meant for Romans?

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    5 years ago, # ^ |
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    It's a project named Lingua::Romana::Perligata, to write Perl codes in Latin.

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    5 years ago, # ^ |
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    No, it was meant for fools.

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

Did anyone have a long queue on custom invocation? It took me about 10 minutes to make sure the UnknownX language is actually ArnoldC; luckily, "It's showtime" title allowed me to start working on the solution before that, but waiting for 10 minutes was weird.

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    5 years ago, # ^ |
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    Oh. I got so much penalty submitting the code just to see the compiler errors :/. Next time I'll use the custom invocation. Thanks for the tip!

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5 years ago, # |
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I failed to submit code (for practice) after contest... :(

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5 years ago, # |
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When can we submit the code after contest....

I want to check whether my H is correct or not.

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5 years ago, # |
  Vote: I like it +10 Vote: I do not like it 
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5 years ago, # |
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first question was damm good . i refreshed my codeforces question site ,checked my wifi just to make sure that that there is no question statement ,the name of question itself was the question . Really enjoyed this contest . it's gave new and exciting experience .

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5 years ago, # |
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Thanks so much for preparing this round ! Love it so much. How could i submit my code right now ?

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    5 years ago, # ^ |
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    The contest should be open for practice now.

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5 years ago, # |
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HASTA LA VISTA, BABY

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

I encountered a strange bug here.

Let's say that we try to get the answer to D from OEIS directly:

import re
import urllib.request

S = input()
with urllib.request.urlopen(f"http://oeis.org/search?q=id:{S}&fmt=text") as page:
    print(re.search(f'%S {S} \d+', page.read().decode()).group(0).split()[-1])

This runs fine on a clean environment with Python 3.7.2, but crashes on CF with error 13131313. The first guess is that the crash is caused by trying to connect to Internet, but that's not the case — import urllib.request already fails and even import _ssl fails with this same error. Since the latter is simply calling the dynamic loader on lib/python3.7/lib-dynload/_ssl.cpython-37m-x86_64-linux-gnu.so, it can't be a network access error.

I tried finding out if someone else had this problem with this error code. The first and only meaningful search result is CF. And guess what, it's about a dynamic library import error, but a different one on PyPy 3. Turns out Python (CPython) 3 on CF can't import some libraries as well.

We could say CF had a custom April 1st prank for me.

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    5 years ago, # ^ |
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    For what it's worth, I've encountered error 13131313 too, when I tried to use import std; in D language (it's an equivalent of #include <bits/stdc++.h> in GNU C++, useful for one-off scripts and short solutions).

    My guess at the time was that importing some libraries toggle a Security Violation custom check at the invoker. Didn't pursue it further though. Sounds more plausible now. Likely the same happens with Python libraries known to deal with internet connections.

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      5 years ago, # ^ |
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      The link with the PyPy case hints that it could be a missing library, i.e. HTTP 404 (or a general 400) instead of 401/403, because that was a problem with _hashlib and I doubt that uses extra system resources. Maybe Mike handles security in most languages simply by purging undesirable elements of the ecosystem.

      In your case, isn't the D compiler still terribly outdated? It could also be that this include just doesn't exist in the CF version.

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        5 years ago, # ^ |
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        Yeah, something seems to happen on the invokers with the libraries viewed as security threats. If they are just removed, it may be possible to track in the repository, pbox.me.

        The D compiler is up to date. When I got that 13131313 error, the compiler was 2.086 (May 2019 version). And it got updated to 2.091 (March 2020 version) just recently, thanks to Mike for that :) .

        Tried again right now, I get a memory limit exceeded instead of 13131313.

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          5 years ago, # ^ |
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          Seems like Memory Limit is something deliberate, tried it on problems with different limits:

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            5 years ago, # ^ |
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            Since import is also a runtime operation, not compile-time like #include, maybe the imported everything counts towards used resources in such a way that the memory runs out. It shouldn't be that large, but I don't know how exactly shared resources are counted and what's checked for MLE. Many recursive DLL/SO loads could hypothetically break it.

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              5 years ago, # ^ |
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              Well, I was testing with D, and import is compile-time there.
              On Testsys with DMD 2.089 (compiling and running a 32-bit Windows executable, same as Codeforces), a similar program with import std; compiles and runs just fine:

              So it's specific to Codeforces invokers.

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                5 years ago, # ^ |
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                import is compile-time there

                Are you sure about that? The docs talk about symbol name lookup, which is often a runtime thing. You definitely can resolve symbols from a "loaded" SO's PLT lazily when they're used during runtime, and you can do that at the program start (when they're loaded) too. I'm pretty sure your stdlib isn't linked statically either.

                This is a linker thing, both compile-time (ld etc) and runtime libdl.so. It's possible that D is using something custom for linking and the CF invoker is mishandling what it wants to do.

                Then again, I don't know about D, just general OS functionality and I'm guessing what the problem could be there. If you could view the startup part of your final executable, go over it step by step and find where it crashes with this error, that would be more productive.

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                  5 years ago, # ^ |
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                  You will be surprised. By default, the dmd Win32 compiler links the standard library statically from a phobos.lib file.

                  Most of it, anyway. There's CURL which has bindings in the standard library, but actually a DLL since it's a third party lib. And indeed importing CURL gets me a Runtime Error.

                  But the Memory Limit effect is something different still.

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                  5 years ago, # ^ |
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                  Huh. I guess the benefits of linking libstdc++.so dynamically don't exist in the case where you have a custom library that isn't used by anything else. Now that I think about it, some OJs use the -static flag to do it in C++ too.

                  So turns out the problem really was dynamic linking. That makes the MLE extra strange since if dynamic linking = security violation, then getting MLE instead = security risk. Well, MLE is either undefined behaviour of the judge or really too much memory allocated somehow.

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5 years ago, # |
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how to solve C?

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5 years ago, # |
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how to solve B ? what are the first and second digit for in output ?

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5 years ago, # |
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I got wa64 on A, help me

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

    May be contest is rated for so that you are getting wa

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5 years ago, # |
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For me problem A was a hint for problem C. C was very interesting.

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

Remark: because of a bug in the "UnknownX" language, the problem H's input format must be concatenated into a single integer, and there are some problems unsolvable with UnknownX.

However, there's a workaround for that: separate the two numbers with 8192 spaces.

This is an accepted code for problem H, modified to take two numbers as input: Try it online!

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

Wow... i really loved giving this contest. It was fun.!!

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5 years ago, # |
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Why hasn't the virtual participation been enabled? :) Would be fun to participate.

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