Nickolas's blog

April Fools Day Contest 2018
By Nickolas, 7 years ago, translation, In English

The contest is over; I hope you've enjoyed it :-) Editorial is here.

The 6th April Fools Day Contest will take place on Sunday April 1st. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

This year I tried to make the problems less puzzling and more versatile. For example, almost all problems have a statement! And you won't need OEIS this time :-)

In this round you'll be given 7 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.

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

Announcement of April Fools Contest 2018
  • Vote: I like it
  • +490
  • Vote: I do not like it

Comments Comments (107)
| Write comment?
»
7 years ago, # |
  Vote: I like it +83 Vote: I do not like it

Last time I had one problem solved; with OEIS problem gone, I wonder about my results now :v

→ Reply
»
7 years ago, # |
  Vote: I like it -69 Vote: I do not like it

I think one of the things this year will be that the contest will start an hour before or after (It will be a nice one).

→ Reply
»
7 years ago, # |
  Vote: I like it +128 Vote: I do not like it

→ Reply
»
7 years ago, # |
  Vote: I like it -176 Vote: I do not like it

plasticBottle?

→ Reply
  • »
    »
    7 years ago, # ^ |
    ← Rev. 3   Vote: I like it -43 Vote: I do not like it

    No.

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it -38 Vote: I do not like it

    Lol now you are going to get upvotes. Not because it was creative, because you are red coder.

    → Reply
    • »
      »
      »
      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      And you're wrong. How unsurprising.

      (I wrote that fully expecting to get downvoted, just to make the forced joke.)

      → Reply
      • »
        »
        »
        »
        7 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        They are downvoting you because of me. People do opposite to what I say. Guys can you upvote this comment? :)

        → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +184 Vote: I do not like it

    A red getting downvotes? April fools came early this year.

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it -30 Vote: I do not like it

    Why don't you delete his comment Mike? You already deleted my comment. Is it because he is red?

    → Reply
    • »
      »
      »
      7 years ago, # ^ |
        Vote: I like it +16 Vote: I do not like it

      I'm sure you deleted your own comment.

      → Reply
      • »
        »
        »
        »
        7 years ago, # ^ |
          Vote: I like it -33 Vote: I do not like it

        You can't delete a comment 5 minutes after it is written mr.smart.

        → Reply
»
7 years ago, # |
  Vote: I like it +12 Vote: I do not like it

As you may probably know, there will be another similar April Fools Contest run by Indonesian coders: TOKI Open Contest Special — April Fools 2018 which will end 1 hour before Codeforces' contest start!

You may use this as an exercise tho, ;)

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +36 Vote: I do not like it

    Additionally, there is a CodeFights Fools' Day Marathon which starts 25 minutes after the Codeforces special round and lasts for 90 minutes. So, one can solve April Fools' problems all day! Or night, depending on where on the globe you are at the moment.

    → Reply
»
7 years ago, # |
  Vote: I like it +18 Vote: I do not like it

I am Exited to be the fool by seeing the statement :D :D :D

→ Reply
»
7 years ago, # |
  Vote: I like it +83 Vote: I do not like it

"And you won't need OEIS this time."

April fool maybe! xD

→ Reply
»
7 years ago, # |
  Vote: I like it -20 Vote: I do not like it

"solving the problem is often easier than figuring out what the actual task is"

Codeforces Round #471 Problem B anyone?

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +44 Vote: I do not like it

    I don't understand how did people not understand that problem... I think most people just didn't read the sentence "Check whether it can be split into two non-empty subsequences such that the strings formed by these subsequences are adorable.", or the sentence "Let's call a string adorable if its letters can be realigned in such a way that they form two consequent groups of equal symbols (note that different groups must contain different symbols)."

    → Reply
»
7 years ago, # |
  Vote: I like it -16 Vote: I do not like it

Well... What if there is not gonna be a contest because April fools :P

→ Reply
»
7 years ago, # |
← Rev. 2   Vote: I like it -18 Vote: I do not like it

The 6th April Fools Day Contest will take place on Sunday April 1st.

No, April 1st is Saturday. :)

UPD: at least I didn't say "Monday" ...

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I suddenly hate this time......I live in China,and that's at almost midnight.Also I will have to be in school!

→ Reply
»
7 years ago, # |
← Rev. 4   Vote: I like it -31 Vote: I do not like it


The contest doesn't exist! Happy April fools' day!

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

almost all problems have a statement??????That's Terribleeeee!

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

Is this UnRated isn't it?

By the way,in Japan,the contest will be held in April 2nd(00:35) lol

UPD:I didn't notice that a RedCoder ask the same question because it gets so many downvotes lol

→ Reply
»
7 years ago, # |
← Rev. 3   Vote: I like it +17 Vote: I do not like it

Thank you Nickolas, for your contests, there are really interesting and unpredictable :D

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

You should increase contest duration.

→ Reply
»
7 years ago, # |
  Vote: I like it +9 Vote: I do not like it

Last year this contest made me mad... WTH, only input and output?... are you kidding me =)

→ Reply
»
7 years ago, # |
← Rev. 4   Vote: I like it +25 Vote: I do not like it

Something will be strange in China...

the contest starts at 23:35 UTC+8, it means after half an hour, it's April 2nd.

Does it mean we should stop joking? Will we be able to see the original problem statement with out jokes?

Seems worse in Japan...

(Joking)

→ Reply
»
7 years ago, # |
  Vote: I like it +10 Vote: I do not like it

Can't wait for this contest, super hyped for the funny questions!

→ Reply
»
7 years ago, # |
  Vote: I like it +8 Vote: I do not like it

at the first sight i took this line for granted "This is a joke competition in which solving the problem is often easier than figuring out what the actual task is."but after going through previous contests ,i could really feel it..XD

→ Reply
»
7 years ago, # |
  Vote: I like it +17 Vote: I do not like it

the problem about April Fools Contest that we can't believe anything you say

you say we won't need OEIS this time this can mean that all the problems can be solved using OEIS

so it's complicated

→ Reply
»
7 years ago, # |
← Rev. 2   Vote: I like it +1 Vote: I do not like it

Problems only have input and output?!!! i think that will be hard.

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

The joke this year is that the servers will go down during the contest.

Wait, isn't every contest an April Fools Day contest? Lol

→ Reply
»
7 years ago, # |
  Vote: I like it +3 Vote: I do not like it

sometimes unrated contests are also necessary ,we can think freely :D

→ Reply
»
7 years ago, # |
  Vote: I like it -12 Vote: I do not like it

Unrated or rated ? Beware you could become a Fool XD

→ Reply
»
7 years ago, # |
  Vote: I like it +7 Vote: I do not like it

right from which you have evolved and left which helps you evolving ...

→ Reply
»
7 years ago, # |
← Rev. 2   Vote: I like it +17 Vote: I do not like it

I think, Problem D can be solved using DP+LCA+Ternary-Search :)

→ Reply
  • »
    »
    7 years ago, # ^ |
    ← Rev. 4   Vote: I like it -63 Vote: I do not like it

    ;c

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +82 Vote: I do not like it

    Please don't give solution hints while the contest is still running. If this happens we'll have to make it unrated. Oh wait...

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

me in the contest XD

→ Reply
»
7 years ago, # |
  Vote: I like it +1 Vote: I do not like it

How to solve D?

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +4 Vote: I do not like it

    I printed the word "black" and it passed.

    → Reply
    • »
      »
      »
      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      I passed with "2nd 12" (and didn't with "black" or "even") I guess, right answer changed time to time.

      → Reply
      • »
        »
        »
        »
        7 years ago, # ^ |
        ← Rev. 3   Vote: I like it 0 Vote: I do not like it

        I have printed "2" two times one time it gave me WA2 another time WA1. So the test cases were random.

        → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +4 Vote: I do not like it

    I bet on even.

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    It was random.

    I actually tested from 0, 00 to 36 looking for the answer.

    But it was to answer any of these "odd", "even". XD

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Printed 1st 12.

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Try betting "Even" until random accepts it :D

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I printed 19 to 36

    1 to 18 failed

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    From the above comments I think that the system spins the roulette when you submit an answer.

    → Reply
»
7 years ago, # |
  Vote: I like it -37 Vote: I do not like it

→ Reply
»
7 years ago, # |
  Vote: I like it +4 Vote: I do not like it

Let me hack D plz xD

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

I`m Unlucky :( are you lucky :P help me to become lucky :D :D

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Can anyone help me in Problem D, I don't know how to do, but I found test 1 change from 3,10,13,36.

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Just bet anything you like. If you win the bet, you get accepted. So just keep submitting something like print('Odd') until you win.

    → Reply
»
7 years ago, # |
← Rev. 2   Vote: I like it +6 Vote: I do not like it

F — 3 sample:

'-' = 45, '1' = 49, '2' = 50 ect. (ASCI)

112 = ( 49 * 10 + 49 ) * 10 + 50 = 5440

-37 = ( 45 * 10 + 51 ) * 10 + 55 = 5065

5440 - 5065 = 375

But how to decide the rest I did not understand...

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    The author of the reference solution, while decoding ascii strings to numbers, accidentally added the plus/minus characters to the next number. Note that to determine the value of a digit, you subtract '0' (=48) from it.

    2+2 = ('2'-'0') + ('+'-'0')*10 + ('2'-'0') = 2 + (-5)*10 + 2 = -46

    The rest follow similarly.

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    112 = (('1' - '0') * 10 + '1' - '0') * 10 + '2' - '0' = 112

    -37 = (('-' - '0') * 10 + '3' - '0') * 10 + '7' - '0' = -263

    112 - -263 = 375

    → Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

How to solve Problem D ?

→ Reply
»
7 years ago, # |
  Vote: I like it +3 Vote: I do not like it

How to solve E ?

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    Count hard and soft. Chessboard alternates color black, white. Find smallest size square chessboard such that we may place all hard in one color, and soft in the other.

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    You are supposed to print out the size of the smallest square chess board that could fit the cheeses if you put hard cheeses on one color of squares and soft cheeses on the other color.

    → Reply
»
7 years ago, # |
  Vote: I like it +1 Vote: I do not like it

How to solve B?

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Once you're certain what type of cat you're dealing with, output "normal" or "grumpy" to standard out.
    You have to print the answer as soon as possible

    → Reply
    • »
      »
      »
      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      I always did 6 checks (from 0 to 5)

      → Reply
      • »
        »
        »
        »
        7 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        You can sometimes do it in one, eg if you see 'no way' then it must be a grumpy cat

        → Reply
  • »
    »
    7 years ago, # ^ |
    ← Rev. 2   Vote: I like it 0 Vote: I do not like it

    check on if "no way", "go die in a hole", "are you serious?", "worse", "terrible".

    the number of checks is not more than 6

    → Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Just follow the problem description. It's clear enough and you don't need to guess anything.

    → Reply
    • »
      »
      »
      7 years ago, # ^ |
      ← Rev. 2   Vote: I like it 0 Vote: I do not like it

      :/ ummm I think not, considering that the point of the contest is to give problem statements that you have to guess at

      → Reply
»
7 years ago, # |
  Vote: I like it +3 Vote: I do not like it

How to solve H?

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    It's quite easy. To get an AC, you don't need to print anything!

    → Reply
»
7 years ago, # |
  Vote: I like it +29 Vote: I do not like it

Lol??

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

Why there was no 'Runtime Error' verdict in problem B? I used asserts but it resulted in WA. I spent ~40 minutes to figure it out.

And how exactly did the input in this problem look? I used asserts to check that the given string is one of the strings from the statement, but it didn't pass so I had to remove them to accept the problem.

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it -16 Vote: I do not like it

    In B, you must output the type of cat as soon as you figure out what type of cat it is.

    → Reply
    • »
      »
      »
      7 years ago, # ^ |
        Vote: I like it +16 Vote: I do not like it

      I know, but it doesn't answer the question why the code

      int main() {
    assert(false);
}

      gets WA and not RE.

      → Reply
      • »
        »
        »
        »
        7 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Hmm, that's interesting... does codeforces ignore asserts, maybe?

        → Reply
        • »
          »
          »
          »
          »
          7 years ago, # ^ |
            Vote: I like it +8 Vote: I do not like it

          Hey man, it's not my first contest on Codeforces :) They work in other problems. Maybe it is specific behaviour for interactive problems, though I haven't ever seen such thing before.

          → Reply
      • »
        »
        »
        »
        7 years ago, # ^ |
          Vote: I like it +6 Vote: I do not like it

        Maybe this is also a part of the April Fool... :P

        → Reply
»
7 years ago, # |
  Vote: I like it +7 Vote: I do not like it

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

In B, I was getting WA checking only given words. Then added "normal" and "grumpy" in the list. Guess what? LOL :p

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

For problem B, I just tried random and it works magic http://mirror.codeforces.com/contest/952/submission/36819128.

→ Reply
  • »
    »
    7 years ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    You can't fool me it's not random.

    → Reply
»
7 years ago, # |
  Vote: I like it +18 Vote: I do not like it

Oh... Although guessing statements is indeed interesting, I prefer problems with complete statements such as B,C and G. Cost a lot of time guessing statements of E and F but didn't solve any one. ╮(╯-╰)╭

→ Reply
»
7 years ago, # |
  Vote: I like it +11 Vote: I do not like it

Is it coincidence that if you use google's I'm feeling lucky on "I'm feeling lucky" you'll see a roulette??

https://www.lifewire.com/im-feeling-lucky-button-1616813

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

How to solve F?

→ Reply
»
7 years ago, # |
  Vote: I like it +22 Vote: I do not like it

I shed tears after I finally knew the truth of D

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

When you got a bug in E and thought that you got the statement wrong...

→ Reply
»
7 years ago, # |
← Rev. 2   Vote: I like it -10 Vote: I do not like it

Problem D was like a hell, I tried 1~36, and "even"/"odd", and many type of "chip in a square" patterns :)

---

|O|

or

===

|0|

or

100,9,25 square of number or

"sqrt(100)" <-- this is still a chip in square * * * Finally, the answer was "Red"...

→ Reply
»
7 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Hi Codeforces community... I was wondering why this contest is not listed in my Contest history ?

Regards!

→ Reply
»
7 years ago, # |
← Rev. 3   Vote: I like it 0 Vote: I do not like it

Awesome!

→ Reply