### Nickolas's blog

By Nickolas, 3 years ago, translation,

The contest is over; I hope at least some of you enjoyed it :-) The editorial is published here.

The 7th April Fools Day Contest will take place on Monday 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. 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.

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

• +446

 » 3 years ago, # |   +1 surprisingly tough ....XD
•  » » 3 years ago, # ^ |   +5 Good one
 » 3 years ago, # |   +45 It's humor and Accepted that create fun.
 » 3 years ago, # |   +17 The best contest of the year :D (not that I perform well in it)
•  » » 3 years ago, # ^ |   +113 I take back my comment.
•  » » » 3 years ago, # ^ |   +11 before contest: so excited !!! after contest: whatever :)))))
•  » » » » 3 years ago, # ^ |   +65 Trying to solve those yes/no problems gets boring quickly when every hypothesis you make turns out to be wrong.
 » 3 years ago, # |   +20 ravioli ravioli, what is in my 1st april contestoly?
 » 3 years ago, # |   +3 I have been waiting for this contest
 » 3 years ago, # |   0 Will this year have April Fool's contests on other platforms? Last year there were other 2 big ones at least, but I couldn't find any this time.
 » 3 years ago, # |   -7 Is it rated?
•  » » 3 years ago, # ^ |   0 No
•  » » 3 years ago, # ^ |   +51 Yes. It's April 1st so yes.
 » 3 years ago, # | ← Rev. 2 →   -8 .
•  » » 3 years ago, # ^ |   -6 boring guy lol :P
 » 3 years ago, # |   +48 Unrated:Let's solve the problems just for fun!I hope everybody have fun.XD
 » 3 years ago, # |   +61 No problem statements plz
•  » » 3 years ago, # ^ |   +52 I am tempted to follow this request, since for one of the problems writing the statement (in two languages) took strictly longer than writing all other pieces of the problem, and it certainly will be the case for another problem... But alas, I aim for variety of jokes above all, so some of the problems have to have a statement :-)
 » 3 years ago, # |   -28 After contest is over : Your rating has been decreased.Happy april fool's day. LOL.
 » 3 years ago, # |   +42 "When the contest begins" Surprise! There is no contest :)
•  » » 3 years ago, # ^ |   +1 "There is contest after 30 minutes, let's open cf" Boom!
 » 3 years ago, # |   -68 Nobody:Me:
•  » » 3 years ago, # ^ |   0 It works XD.
 » 3 years ago, # |   +15 A classified source just confirmed that this round will be rated :P :P :P
 » 3 years ago, # |   +22 It's April Fools, so during the contest suddenly it will become rated =)
 » 3 years ago, # |   -8 Why unrated? :(
•  » » 3 years ago, # ^ |   +9 I think it will be rated and open hack. because today is fools day
 » 3 years ago, # |   0 it's unrated, i hope so.. XD
 » 3 years ago, # |   +2 It's April 1st, the contest may suddenly starts 2 hour earlier XD
•  » » 3 years ago, # ^ |   0 really?
 » 3 years ago, # |   +7 2012,2013,2014-2016,2017,2018 Mathematically, u shouldnt be doing an april-fools contest this year o.O
 » 3 years ago, # | ← Rev. 2 →   +36 I hope, in this year, this will not happen with me ...
•  » » 3 years ago, # ^ | ← Rev. 2 →   +8 It was normal that you got wrong answer. You had to make a program that makes 2 good bets in roulette. The results were made randomly (like in normal roulette). The best strategy was to bet on red or black (even or odd), because you have 48.6% that your bet will be good. That means 23.6% chance to pass main tests (only 2 test cases). While the results were random, the Answer section were made by the code of author that got accepted, so that can't be always good. In your case the result was 10 (black), so you got WA.
•  » » 3 years ago, # ^ |   0 so, can I ask what is the contest id of the problem?
•  » » » 3 years ago, # ^ |   0
•  » » » » 3 years ago, # ^ |   +1 Thanks
 » 3 years ago, # | ← Rev. 2 →   +57 To all the other teams which are attending ICPC WF, let's join this contest together! SpoilerHA CYKE I AM NOT ATTENDING ICPC WF HAPPY APRILS FOOLS SpoilerHa... Haha....
 » 3 years ago, # |   0 Exciting！
 » 3 years ago, # | ← Rev. 2 →   -8 This is my first April Fool's Day contest. exciting!!!
 » 3 years ago, # | ← Rev. 4 →   0 Fools Day happy~~ : )
 » 3 years ago, # |   +11 This contest won't get rated afterwards, right?
•  » » 3 years ago, # ^ |   0 No one knows. It is April's fools contest, anything can happen :D
 » 3 years ago, # |   0 I hope I won't become a fool after this contest :3
 » 3 years ago, # | ← Rev. 2 →   +75 The 7th April Fools Day Contest will take place on Monday April 1st. Nickolas It's 32nd march, fix it.
 » 3 years ago, # |   -14 Is it rated??
•  » » 3 years ago, # ^ |   0 No.
 » 3 years ago, # |   -6 fool time .?
 » 3 years ago, # |   -12 real fun
 » 3 years ago, # | ← Rev. 2 →   -18 chutiyaap
 » 3 years ago, # | ← Rev. 5 →   0 Spoilerand then you got WA because you print 4 but you should print "any number"
•  » » 3 years ago, # ^ |   +1 :)
 » 3 years ago, # |   +97 Goodluck and have fun everybody!
 » 3 years ago, # |   0 It is should be April fools night contest for me :3
 » 3 years ago, # |   +11 The image in the Russian version of 1145C - Mystery Circuit is broken for some reason, here is what it should be:
•  » » 3 years ago, # ^ |   +1 Should've supported Q# submission, missed opportunity. Tssk tssk.
 » 3 years ago, # |   +1 It's the first time I get rank1.I'm so happy.XD
 » 3 years ago, # |   0 Wonder how the editorial will look like...
 » 3 years ago, # |   +1 D has great speiling
•  » » 3 years ago, # ^ |   +22 I warned you, we didn't proofread the statement at all :-)
•  » » » 3 years ago, # ^ |   +5 Did you proofread the sample testcases?
•  » » » » 3 years ago, # ^ |   +13 Yes, those are numbers, much easier to check :-)
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 ans is just Xor ;)
•  » » » 3 years ago, # ^ |   0 Don't tell me it was joke
•  » » » » 3 years ago, # ^ |   0 yes it was a joke XD
•  » » » » 3 years ago, # ^ |   0 you got April fooled
•  » » » » » 3 years ago, # ^ |   +1 guessed Xor using D'Or
 » 3 years ago, # |   +137 Due to the unethical and ugly behavior of some members of the community, this round will be rated. Let's solve problems just for fun!
 » 3 years ago, # | ← Rev. 2 →   +9 Please post the editorial as soon as possible. Eagerly waiting (to submit :P).
•  » » 3 years ago, # ^ |   0 http://codeforces.com/blog/entry/66327The solutions for other two problems coming up soon...
•  » » » 3 years ago, # ^ |   +8 Too late friend Nickolas, Round is over now. :D
 » 3 years ago, # |   +4 How are so many people solving D can anyone post the answer :D :P
 » 3 years ago, # |   +9 Toughest Constest ever Can't even go through the problem statements.
 » 3 years ago, # |   +40 I have seen some previous years April Fools Contest problems but this is the lamest April Fools Contest of all time. No offence
 » 3 years ago, # |   +22 Tutorial for problem B please :)
 » 3 years ago, # | ← Rev. 2 →   +11 I made a bet with my senior ray-asuka that if I could not become a candidate master before my birthday（4.2）, I would invite him and my teammates to dinner. This round was my last chance, and he got his wish.
•  » » 3 years ago, # ^ |   +11 best wishes
•  » » 3 years ago, # ^ |   +6 as the old saying in China, the most rich man never pubilsh his opinion with someone
 » 3 years ago, # |   0 Paper
•  » » 3 years ago, # ^ |   0 No interactive AI on CF confirmed. :/
 » 3 years ago, # |   +8 Felling like a real fool :(
 » 3 years ago, # |   +24 two plus xor of third and min element?
•  » » 3 years ago, # ^ |   0 YES!
•  » » 3 years ago, # ^ |   +28 how did you even come up with that solution?
•  » » 3 years ago, # ^ |   +5 How did people guess this on the first attempt, with only one sample case?
•  » » » 3 years ago, # ^ | ← Rev. 2 →   +3 It's the wrong letters, they make up sentence.
•  » » » » 3 years ago, # ^ |   0 true... nice logic man !
•  » » » 3 years ago, # ^ |   0 exactly !! how ??Xor seems intuitive... but what about min^3rd + 2 ...Its impossible without extra hints
•  » » » 3 years ago, # ^ |   +2 Note that there are typos in the statement. Write down all the letters that should be replaced by some other letter for the correct spelling. This is the message you get.
 » 3 years ago, # |   +40 My solution for E: if $i$ gives remainder 1, 4 or 5 mod 6, then yes. Sadly, it's a wrong solution, but it perfectly fits.
•  » » 3 years ago, # ^ |   0 ye, I also trusted oeis :(
•  » » 3 years ago, # ^ |   0 SAME :(
•  » » 3 years ago, # ^ |   0 Same :-)
•  » » 3 years ago, # ^ |   0 wow. exactly same to me
 » 3 years ago, # | ← Rev. 3 →   +35 ((min(id,25)+id)%(2+id%3))>0I found it after 1min of the contest...THAT'S AWESOME!UPD: Problem E
•  » » 3 years ago, # ^ |   +5 And where did this magical condition come from?
•  » » » 3 years ago, # ^ | ← Rev. 2 →   +26 It comes from the Fourier transformation of the image 1 to 20. (my poor English :D
•  » » » » 3 years ago, # ^ |   +6 Well played :)
•  » » 3 years ago, # ^ |   +29 $\{[\min(\mathrm{id},25)+\mathrm{id}]\bmod(2+\mathrm{id}\bmod3)\}>0$That's neat!
 » 3 years ago, # |   0 Editorials please!
 » 3 years ago, # |   +3 Well, I managed to brute force B after 50 attempts...
•  » » 3 years ago, # ^ |   +8 i do the same for problem C :)
•  » » » 3 years ago, # ^ |   +15 I made the same for both :P
•  » » » 3 years ago, # ^ |   0 How do you bruteforce C when you need to guess a number? Seems like it would take a lot more attempts :o
•  » » » » 3 years ago, # ^ |   0 Tests turned out to be ordered by numbers in their input)
•  » » » » 3 years ago, # ^ |   0 I made it with supposing that the answer is also between 0 and 15. I wasn't sure on it, but I tried it. Later I noticed that each number has different answer.
•  » » » » 3 years ago, # ^ |   0 Input has 4 bit. Circuit looks like some kind of bit shuffling / adding. So we can guess that output is in range [0, 15] and has some kind of pattern.--> basically just submit some educated guess. You can look at my submissions to see how I guessed it.
•  » » 3 years ago, # ^ |   0 curious about how to brute force on YES/NO problems
•  » » » 3 years ago, # ^ | ← Rev. 2 →   +5 Make sure it answers correctly for first 4 tests. Then try to get 5th test with binary search — answer no to everything (else), then yes to 50..99, etc. Eventually I realized the test cases are in increasing order which made things a lot easier — just need to find the next value to "flip" the answer on.That's pointless on any serious contest because the number of attempts it takes will give you around 0 points.
 » 3 years ago, # |   +110 You: TWOPLUSXOROFTHIRDANDMINELEMENTMe, an intellectual: LTABRACCANEPGZEFBOHPNOSIFASOMC
•  » » 3 years ago, # ^ |   +37 An intelleqtual
•  » » 3 years ago, # ^ |   +14 I knew this fact quickly because i use google translator... kk
•  » » 3 years ago, # ^ |   0 And wtf is that "mine element" :|? Got this message pretty quickly but had no idea what to do with it.
•  » » » 3 years ago, # ^ |   0 Notice how there is only 1 e, not 2 e(minelement isn't mineelement).
•  » » » » 3 years ago, # ^ |   +24 fuck
•  » » » 3 years ago, # ^ |   0 I guess it is "min" element. btw which message are you talking about?
•  » » » » 3 years ago, # ^ |   +1 By message I meant hidden statement "two plus (...)"
•  » » » 3 years ago, # ^ |   +10 fece is a correct word, so MIN element ...
•  » » » » 3 years ago, # ^ |   0 ... but it took me half an hour to figure it out :D Also had MINE there at first ...
•  » » 3 years ago, # ^ |   +18 SBEVE
 » 3 years ago, # | ← Rev. 3 →   -8 1% of time to read statements, 99% of time to guess and attempt, lol
•  » » 3 years ago, # ^ | ← Rev. 2 →   +8 You missed 1% (I wrote it before he edited his comment).
•  » » » 3 years ago, # ^ | ← Rev. 2 →   -8 Aha, 1% for attempting to submit.
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 The 1% was wasted... ;-D
•  » » » 3 years ago, # ^ |   0 Seems some guys did not agree with my humor and downvoted for it. :(
•  » » » » 3 years ago, # ^ |   0 I also got massively downvoted for some other comment on that day. Seems some didn't appreciate that contest to the point of being in really bad mood...
 » 3 years ago, # |   0 Why can't I view others' solutions? System Checks?
 » 3 years ago, # |   0 Only one task... Ahahahah, the best contest)) I want more!
 » 3 years ago, # |   0 my wrong solution for C: A circle with cross indicates 4(because of cross); A dot indicates 1(because it's a dot); Note that the input number is between 0 and 15, so make it become binaries. for the example: 3->0011->the last line(4+1+1+1) + the third line(4+1+1) =13;I think this is reasonable but got WA , sad...
•  » » 3 years ago, # ^ |   0 It's actually just some quantum logic gates of 4 bits.
•  » » » 3 years ago, # ^ |   0 QUANTUM LOGIC GATES?Apparently ,this isn't a NEAT WORD.
•  » » 3 years ago, # ^ |   0 Yes, you are right, but you need to turn the number(n) given to us, and only then calculate according to the scheme. After, reverse result and transfer to the decimal numeral system. Read this article: https://en.wikipedia.org/wiki/Toffoli_gateВ общем почитайте статью https://en.wikipedia.org/wiki/Toffoli_gate (есть на русском). Надо тип перевести n в 2-ую систему счисления, перевернуть число, посчитать по схеме, потом перевернуть результат и перевести в 1-ую систему
 » 3 years ago, # |   +30 Use the most foolish way to spend April Fools' Day lol！！！
 » 3 years ago, # | ← Rev. 2 →   +35 I am so happy to be the second person to solve problem C!!All because I listened carefully in the [Quantum Computing] class when COIWC2019(Chinese Olympiad in Informatics — Winter Camp)!!
•  » » 3 years ago, # ^ |   +22 lol Are you taking quantum computing classes for the Olympiad?
•  » » » 3 years ago, # ^ |   +19 I don't know XXDD! Isn't that crazy!!??
•  » » 3 years ago, # ^ |   +23 And wtf is that problem about?
•  » » » 3 years ago, # ^ |   +22 It's just a Controlled Not gate. https://en.wikipedia.org/wiki/Controlled_NOT_gate
•  » » » 3 years ago, # ^ |   +14 4 bits 1-2-4-8The symbols represents NOT, CNOT, TOFFOLI gates etc.[https://en.wikipedia.org/wiki/Quantum_logic_gate#Controlled_(cX_cY_cZ)_gates](https://en.wikipedia.org/wiki/Quantum_logic_gate#Controlled_(cX_cY_cZ)_gates)Don't ask me why is this used in April's Fool instead of Q# winter
•  » » 3 years ago, # ^ |   +23 OMG! I thought they are XOR gates because they were like xor symbol.
•  » » 3 years ago, # ^ |   -8 %%%great great pinkrabbit
 » 3 years ago, # |   +73 Why the problem B wants to ban KAN? Just a joke
 » 3 years ago, # |   0 in D i used grammarly to get the grammatically correct sentence to make it readable. rip
 » 3 years ago, # |   -26 Solution of A:N/4
•  » » 3 years ago, # ^ |   0 really? i brute forced the whole solution :P
•  » » » 3 years ago, # ^ |   0 yes ,Check it Dude
•  » » 3 years ago, # ^ |   0 In the first test case n was 4 but the answer was 4 not 1
 » 3 years ago, # |   -8 For B:There Is a "YES" in Her "NO".iywim
 » 3 years ago, # |   0 Now I regret because I voted that I love this contest before it starts..