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!
And congrats to the first solvers!
- A: zscoder
- B: KeNaj712
- C: conqueror_of_tourist
- D: namcartoon06
- E: SanguineChameleon
- F: A_G
- G: lethan3
- H: InternetPerson10
- I: aberent (the only person who solved it in contest!)
- J: mxdcxt
UPD4: Sorry for the inconvenience, the contest is now open for practice submissions + virtuals.
As an author, give me contribution
You're not getting anything unless you ask nicely 😠
nice foreshadowing
Please Give Me Accepted :uwu:
OMG THIS WAS A HINT!
Funny I somehow managed to crack...
OMG, I should have seen this earlier
Deeemmmmnnnnnn, Sly AF
Editorial- Editorial Link
Happy April Fools Day :)
haha, my Youtube display ads first so I’m not being rickrolled :)
Who Tested?
1663A - Who Tested?
I remember thinking about its solution last year for more than an hour and couldn't solve it. Smiled when I saw the solution.
not BucketPotato
You tested.
Make it rated
Is it rated?
Is it rated?
Is it rated?
Is it rated?
Is it rated?
Is it rated?
Is it rated?
1812B - Was it Rated?
It is overrated.
My first april fool contest. Hope it would be funny
Ac round 5
Hoping it to be unrated like last time :)
well it's written there
I guess people didn't understand my sarcasm, explaining my joke to you :)
Last time on the announcement they wrote that it's unrated but after the contest rating change happened and many people lost their ratings xD
I am from Switzerland.
I am from Mars Elon Musk brings me to the earth
I am from a parallel universe and I came here using black holes
I am from zoo and I came here for bananas.
I can't hold my laughing
Is this actually unrated or is that a prank ..?
Just join, I'm sure you will love it !
I wish to see the foolest problems ever made in codeforces!
I read some of past years problems and understood none of them :/ is it normal?
That's kind of the point
Is it rated ?
yes!
ok, I pull up!!!
ok we pull up!
Okay, so this year I have to print willy108 :)
If the checker gets access to data about submitter, probably you would have to print do4z :-)
Every previous years questions SHOCKED me, especially last year's first question lol
Are the problems somehow related to the tasks in Ohio?
i am sure yes
Ahhh .. you should have told it's rated. And after contest, surprise!
Or maybe it is the reverse?
at the end when it's time to begin the contest you will say we make you fool there is no contest today.
Good luck!
As a commentator, give me a contribution
Please upload the editorial as soon as possible!
Much needed
Lol, my best performance on codeforces was in contest for fools
me participating for the first time in april fool contest:
SecondThread Please tel me you will upload screencast of the contest :D
lmao, I was hoping for the same.
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 $$$\newline$$$
B -> 15,20,21 no else yes E -> print 100000 , Hell of a contest xD
why 15, 20, 21 no?
15th, 20th, and 21th contests were unrated.
I kinda figured it out, but how to know ?
look at standings of each contest and if it doesn't say rating changes then the round was unrated.
D could also be: print(negative integer)
Yes, I did print(-1)...from wikipedia
In problem D, I just printed -1. I got it after equating $$$(3*x+1)/2 = x$$$ and got $$$x=-1$$$.
wtf how to solve F? I tried to delete a numbers to 7,13,19 and my draft was corrupted
How F QAQ
If you prime factorize the smaller number, you'll see that it's all 9s, with one 1. You can figure this out with Wolfram Alpha or Pollard Rho.
You can check all possible variants of all 9s+a one in a couple seconds against the big number with BigInteger.
Great contest. Solved ABDEFJ.
Hello, jury! please give me AC!
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?
cf round 15, 20 and 21 were unrated
Oh, I see. During the contest all blogs including announcements were blocked and I didn't realize you can check if a contest is rated from the standings page.
some people got it in under 5 mins though, i don't know how
Contest 15, 20, and 21 is unrated
Read problem name, Codeforces Beta rounds 15, 20 and 21 were unrated.
Beta/Alpha rounds?
Damn, I went to https://mirror.codeforces.com/contests?complete=true and I found 15 contests ago there was: https://mirror.codeforces.com/contest/1776 which was unrated as an online mirror of SWERC and 25 contests ago there was: https://mirror.codeforces.com/contest/1780 which also was unrated due to some issue with some problem. Sadly matched the 15 from the sample...
I did the same thing... I thought n means last n contests
Now contest is over. Can you please tell me what was that dammnn mysterious language!!!
ChatGPT
please
it's what you have to say to the judge xD
ask kindly
you have to use the word "pls" or "please" and then submit
and what was the logic behind entering this :)
You can look at your submission record, it will tell you to beg him for help
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.
Lol! that was a nice observation XD
english
you had to ask judge to give you AC...
"can you please give me AC?"
If you miss "please" then it won't give you AC. Jury was so rude >_<
In fact it's English. Submit "Please create a mysterious language." and you'll get an AC
Zeroforces round
Contest not for fools...
The best round ever (with pinely round)
Because there were no geometry problems?)
problem E?
What about its name
How to solve C? I think it might relate to 3, 1, 4.
You have the answer
pi=acos(-1.0)....
sample choice in C was genius
Firstly I assumed we split sample as $$$[3, 2, 3]$$$, OEIS'd it, and it found $$$[3, 2, 3]$$$ as one of the first digits in pi. Then I insta realized that $$$[3, 1, 4]$$$ is also correct split, and solution became obvious. I dont know was it intended or not, but it was very cool.
Please!, allow the practice...
ASAP,
Thank you
G????
got trolled so hard by D
Who spent several minutes trying to find long Collatz sequences for D like me? :raising_hand:
Hell yeah...
I spent 1 hour
I tried generating random 1000 digits numbers and checking whether they are greater than k... It went well for about k < 20000
$$$2^{3321} - 1$$$ needs $$$45301$$$ steps to reach $$$1$$$. That's the best I could find.
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.
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
How did you come up with this?
There's an easier sequence for problem D 0 -> 0 -> 0....
This was a lot of fun, thank you :)!
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?
It asks whether the n-th round on Codeforces was rated. Specifically, beta rounds 15, 20 and 21 were unrated
In the first 25 rounds of codeforces's history, round 15, 20 and 21 were unrated.
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.
What is the solution process for I?? Solution for I makes no sense to me
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.
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.
please make it rated
Last year, it is, for one day :D
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.
How do they got accepted for the second problem(was it rated?) without the wrong answer?
just cheating
Or maybe they correctly guessed that it was — whether the $$$n$$$ th round of Codeforces was rated or not.
correctly guessed from 2**25 possibilities?? bullshit!
You're too arrogant
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.
we are talking about guessing without wrong submissions lol
Ohh didn't saw that, thanks for reminding
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.
You needed to check which of the first 25 codeforces contests were rated.
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.
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?
You can open the standings table of a contest and if the rating changes option is absent, then it is unrated :D
This was my 1st april fool contest and Really, after giving this contest , I am feeling like April fool celebrated now :-)
Happy to see an April Fools Day Contest with no domain knowledge such as plots or characters in a specific movie. Great contest!
Is J judged by a LLM or a bunch of ifs?
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! :)
amazing! Problom J is so interesting. Did you judge it by a LLM?
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
Please do the rating update quickly and make me CM >_<
the one who got I is a genius
Thanks, you successfully proved I am a fool.
https://mirror.codeforces.com/contest/1812/submission/200195600 How didn't this get AC?
the same way this got AC
https://mirror.codeforces.com/contest/1812/submission/200186621
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)
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.
The maximum that I could generate is for $$$n = 2^{3300} - 1$$$. The sequence length is $$$45280$$$ for this number.
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.
I found $$$n = 2^{3321} - 1$$$ (during contest). The sequence has length $$$45302$$$.
https://oeis.org/A277109
for $$$n = 2^{1812}+1$$$ , the length is $$$67108863$$$
I submitted this number, but got Wrong Answer :(
The sequence length is actually $$$12969$$$. The OEIS sequence that you have linked here is actually for "the length of the longest sequence of consecutive numbers which all take the same number of steps". This is different.
Sorry, my toothache really hurt :(
Got AC for n = 274133054632352106267, found here: https://www.fit.vut.cz/research/publication-file/12315/postprint.pdf
Actually, that number only takes $$$1805$$$ steps. It only works because you forgot about overflow and it's getting overflowed into negatives.
I submitted n=0
just print 0 and boom, AC.
What is the Solution of
It was rate problem?
Check first 25 contests on Codeforces which were rsted and which were not
or just make 30+ submissions
Problem G: If you download the image and check the hex code, you will get
01722b, which is the problem 1722B - Colourblindness.Man I checked the rgb but I tunnel visioned on R=1 lol.
This contest is disaster, total waste of time.
You could've seen rounds in previous years and known that they're a waste of time before actually doing it
I don't think any one do that.
No you're just an idiot
Thanks ChatGPT for answering questions!
one of the funniest accepted ever
Will upsolving be available?
When can I send solutions if I can't do it virtual
Why I can't submit my code?
Where is the editorial? I want to know the solutions :)