flamestorm's blog

April Fools Day Contest 2023
By flamestorm, 20 months ago, In English

Hello, Codeforces!

I, along with AlperenT, Ari, BucketPotato, ScarletS, and ToxicPie9, would like to invite everyone on Codeforces to the April Fools Day Contest 2023! The 11th April Fools Day Contest will take place on Apr/01/2023 17:35 (Moscow time). This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

Please note that the round is unrated.

In this round you'll be given $$$n$$$ weird problems and 2 hours to solve them, where $$$7 \leq n \leq 12$$$. At most $$$\sqrt{n}$$$ of the problems will be interactive. 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).

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, 2020, 2021, 2022.

Good luck, and have fun!

UPD1: Thanks willy108 for testing!

UPD2: The editorial is released!

UPD3: Congrats to the winners!

  1. InternetPerson10
  2. Geothermal
  3. A_G
  4. Maksim1744
  5. LJC00118

And congrats to the first solvers!

UPD4: Sorry for the inconvenience, the contest is now open for practice submissions + virtuals.

  • Vote: I like it
  • +576
  • Vote: I do not like it

Comments Comments (180)
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20 months ago, # |
  Vote: I like it +282 Vote: I do not like it

As an author, give me contribution

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20 months ago, # |
  Vote: I like it +50 Vote: I do not like it

Who Tested?

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

Make it rated

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

My first april fool contest. Hope it would be funny

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

Ac round 5

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

Hoping it to be unrated like last time :)

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    20 months ago, # ^ |
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    well it's written there

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

      I guess people didn't understand my sarcasm, explaining my joke to you :)

      Spoiler
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20 months ago, # |
  Vote: I like it -6 Vote: I do not like it

I am from Switzerland.

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20 months ago, # |
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Is this actually unrated or is that a prank ..?

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    20 months ago, # ^ |
      Vote: I like it +12 Vote: I do not like it

    Just join, I'm sure you will love it !

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

I wish to see the foolest problems ever made in codeforces!

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

I read some of past years problems and understood none of them :/ is it normal?

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20 months ago, # |
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Is it rated ?

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

ok, I pull up!!!

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20 months ago, # |
  Vote: I like it +16 Vote: I do not like it

Okay, so this year I have to print willy108 :)

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

    If the checker gets access to data about submitter, probably you would have to print do4z :-)

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20 months ago, # |
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Every previous years questions SHOCKED me, especially last year's first question lol

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

Are the problems somehow related to the tasks in Ohio?

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20 months ago, # |
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Ahhh .. you should have told it's rated. And after contest, surprise!

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

at the end when it's time to begin the contest you will say we make you fool there is no contest today.

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

Good luck!

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

As a commentator, give me a contribution

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

Please upload the editorial as soon as possible!

Much needed

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

Lol, my best performance on codeforces was in contest for fools

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20 months ago, # |
  Vote: I like it +11 Vote: I do not like it

me participating for the first time in april fool contest:

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20 months ago, # |
  Vote: I like it +16 Vote: I do not like it

SecondThread Please tel me you will upload screencast of the contest :D

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

Hints: $$$\newline$$$ A: print("security") $$$\newline$$$ D: print(0) (0/2 = 0 — so we disproved the collatz hypothesis:)) $$$\newline$$$ E: print(0) (any number here) $$$\newline$$$ J: give me AC $$$\newline$$$

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

    B -> 15,20,21 no else yes E -> print 100000 , Hell of a contest xD

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      20 months ago, # ^ |
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      why 15, 20, 21 no?

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

        15th, 20th, and 21th contests were unrated.

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          20 months ago, # ^ |
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          I kinda figured it out, but how to know ?

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

            look at standings of each contest and if it doesn't say rating changes then the round was unrated.

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    20 months ago, # ^ |
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    D could also be: print(negative integer)

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      20 months ago, # ^ |
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      Yes, I did print(-1)...from wikipedia

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

    In problem D, I just printed -1. I got it after equating $$$(3*x+1)/2 = x$$$ and got $$$x=-1$$$.

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20 months ago, # |
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wtf how to solve F? I tried to delete a numbers to 7,13,19 and my draft was corrupted

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20 months ago, # |
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How F QAQ

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    20 months ago, # ^ |
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    Spoiler
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20 months ago, # |
← Rev. 6   Vote: I like it +9 Vote: I do not like it

Great contest. Solved ABDEFJ.

Python code for solving F
My answer for J
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20 months ago, # |
  Vote: I like it +3 Vote: I do not like it

What is the solution of B? I got it by trying 40+ times (15, 20, 21 are NO, others YES) but what is the logic?

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20 months ago, # |
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Now contest is over. Can you please tell me what was that dammnn mysterious language!!!

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

    ChatGPT

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    20 months ago, # ^ |
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    please

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

    you have to use the word "pls" or "please" and then submit

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      20 months ago, # ^ |
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      and what was the logic behind entering this :)

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        20 months ago, # ^ |
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        You can look at your submission record, it will tell you to beg him for help

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

        I asked the jury "what do you want?" to which the jury replied "wrong answer I can give you AC, but did you forget something important?", from there I remembered this comment — and added "pls" lol.

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

    english

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

    you had to ask judge to give you AC...

    "can you please give me AC?"

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

      If you miss "please" then it won't give you AC. Jury was so rude >_<

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    20 months ago, # ^ |
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    In fact it's English. Submit "Please create a mysterious language." and you'll get an AC

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

Zeroforces round

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20 months ago, # |
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Contest not for fools...

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20 months ago, # |
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The best round ever (with pinely round)

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

How to solve C? I think it might relate to 3, 1, 4.

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

sample choice in C was genius

Spoiler to the problem
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20 months ago, # |
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Please!, allow the practice...
ASAP,
Thank you

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

G????

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

got trolled so hard by D

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20 months ago, # |
  Vote: I like it +9 Vote: I do not like it
my code for B
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20 months ago, # |
  Vote: I like it +91 Vote: I do not like it

Who spent several minutes trying to find long Collatz sequences for D like me? :raising_hand:

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

    Hell yeah...

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

    I spent 1 hour

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

    I tried generating random 1000 digits numbers and checking whether they are greater than k... It went well for about k < 20000

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

      $$$2^{3321} - 1$$$ needs $$$45301$$$ steps to reach $$$1$$$. That's the best I could find.

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

Solution A-E

A:read the picture:security

B:note that it is "was it rated". you can find that codeforces round 1 is rated and round 15 is unrated. In the first 25 test,only round 15,20,21 are unrated.

C:t<=32 and sum of n<=155,around t*5, so you can guess that it is n is a random number between 0 to 9. As 2*1*4=8,7=7,1*2*3*5=30, you can guess that n is 31415926... and the answer is the product. the sum of the first 32 digits of pi is also actually equal to 155.

D:there is no limit of n>0.

-7 -> -20 -> -10 ->-5 -> -14 -> -7

E:the difference is 10^6 not 10^-6. if you set a=0,the condition will be always satisfied.

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

    F : Both the given numbers have a factor if the type [(bunch of 9s) 1 (bunch of 9s)]. Check for all of them upto the number's length and find the other factor by division

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

    There's an easier sequence for problem D 0 -> 0 -> 0....

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

This was a lot of fun, thank you :)!

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

    Hii. Could you solve the was it rate problem? I tried too many methods but I could not solve it. Can u explain me how did u solve it?

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

      It asks whether the n-th round on Codeforces was rated. Specifically, beta rounds 15, 20 and 21 were unrated

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

      In the first 25 rounds of codeforces's history, round 15, 20 and 21 were unrated.

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

My best performance came in an April fool contest lol. Can't wait for my rating to increase. Important life lesson, I will always remember to say please to the AI overlord who is going to take over.

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

What is the solution process for I?? Solution for I makes no sense to me

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

    A person is climbing a mountain. We notice that the vertical line of the letter 'b' is upward, indicating that the person has moved up one unit. The vertical line of the letter 'p' is downward, indicating that the person has moved down one unit. Count all letters in the string that have this up-down feature. Increase the count by 1 when encountering an upward letter, and decrease it by 1 when encountering a downward letter. The initial height is 0. Output NO only when the height becomes negative at some point or the person finishes climbing the mountain (processing the entire string) with a non-zero height. Otherwise, output YES. That's my inference.

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

    English letters have "ascenders" and "descenders": ascenders are parts of a letter that extend above a baseline, descenders parts that extend below. For example, normal letters are "a", "x" or "z", letters with ascenders are "f", "l" or "k", letters with descenders are "y", "g", "j" etc.

    So apparently the idea is that you keep track of the height and you increase by 1 when you encounter an ascender, decrease by 1 if you encounter a descender. A word is valid if you start and end at 0 without going below 0.

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

please make it rated

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

Thanks for this contest, made my day!

Also binary searching to deduce each test case for B was fun XD, later I noticed there were few "NO"s so guessed the 22nd test case but was fun lol. Most submissions I have ever made in a contest.

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

How do they got accepted for the second problem(was it rated?) without the wrong answer?

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

    just cheating

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

      Or maybe they correctly guessed that it was — whether the $$$n$$$ th round of Codeforces was rated or not.

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        20 months ago, # ^ |
          Vote: I like it -29 Vote: I do not like it

        correctly guessed from 2**25 possibilities?? bullshit!

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

          You're too arrogant

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

          actually you don't need 2^25 (and btw its 2^23 cuz there are two examples), you only need to keep doing binary searches with the 25 numbers using submissions and then you can find the other two unrated numbers.

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

            we are talking about guessing without wrong submissions lol

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              20 months ago, # ^ |
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              Ohh didn't saw that, thanks for reminding

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

    I went to the standings page (eg: https://mirror.codeforces.com/contest/15/standings) and checked to see if the "Rating Changes" tab was there or not.

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

    You needed to check which of the first 25 codeforces contests were rated.

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

    I looked at the cached versions of the announcement blogs on Google for each of the contests (blogs were disabled at the time I solved the problem) to see if the contest was rated.

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

    I opened the first 25 contests and checked if it's rated or not

    the unrated contests of 25 contests are 15 20 21

    I solved it using the problem name it's rated?

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

      You can open the standings table of a contest and if the rating changes option is absent, then it is unrated :D

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

This was my 1st april fool contest and Really, after giving this contest , I am feeling like April fool celebrated now :-)

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20 months ago, # |
  Vote: I like it +47 Vote: I do not like it

Happy to see an April Fools Day Contest with no domain knowledge such as plots or characters in a specific movie. Great contest!

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

Is J judged by a LLM or a bunch of ifs?

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

Was quite frustrated with multiple wrong answers for D, but couldn't help laughing out loud when I saw the solution. XD
Great problems, keep it up! :)

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

amazing! Problom J is so interesting. Did you judge it by a LLM?

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

It's very funny reading the inputs of participants for last question (Unmysterious Language).But finally it seems like we must use the word "Please" for AC

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

Please do the rating update quickly and make me CM >_<

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

the one who got I is a genius

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

Thanks, you successfully proved I am a fool.

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

https://mirror.codeforces.com/contest/1812/submission/200195600 How didn't this get AC?

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

How does the spj for D work?

Are there any conclusions that $$$\forall 1\le n \le 10^{10^3}$$$, it will finally become $$$1$$$ in less than $$$10^{18}$$$ times?(That is, all positive integers do not work)

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

    The author set $$$k \le 142\,023$$$ ($$$1\,4\,2023$$$) to make the checker work quickly, the $$$10^{18}$$$/redacted business was intended as a bit of a red herring.

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

      The maximum that I could generate is for $$$n = 2^{3300} - 1$$$. The sequence length is $$$45280$$$ for this number.

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

        Collatz seems to have logarithmic length,so I doubt there is a positive integer under $$$10^3$$$ digits that has a sequence longer than $$$10^{18}$$$. The answer for the problem is a nonpositive integer.

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

        I found $$$n = 2^{3321} - 1$$$ (during contest). The sequence has length $$$45302$$$.

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

      https://oeis.org/A277109

      for $$$n = 2^{1812}+1$$$ , the length is $$$67108863$$$

      I submitted this number, but got Wrong Answer :(

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    20 months ago, # ^ |
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    just print 0 and boom, AC.

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

What is the Solution of

It was rate problem?

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

    Check first 25 contests on Codeforces which were rsted and which were not

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

Problem G: If you download the image and check the hex code, you will get 01722b, which is the problem 1722B - Colourblindness.

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

    Man I checked the rgb but I tunnel visioned on R=1 lol.

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20 months ago, # |
  Vote: I like it -30 Vote: I do not like it

This contest is disaster, total waste of time.

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

    You could've seen rounds in previous years and known that they're a waste of time before actually doing it

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20 months ago, # |
← Rev. 2   Vote: I like it +66 Vote: I do not like it

Thanks ChatGPT for answering questions!

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20 months ago, # |
  Vote: I like it +24 Vote: I do not like it

one of the funniest accepted ever

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

Will upsolving be available?

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20 months ago, # |
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When can I send solutions if I can't do it virtual

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

Why I can't submit my code?

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

Where is the editorial? I want to know the solutions :)

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