McDic's blog

Codeforces Round #566 (Div. 2)
By McDic, history, 6 years ago, In English

안녕하세요, 코드포스! (Hello, Codeforces!)

I'm super happy to introduce you to Codeforces Round #566 (Div. 2), which will take place on Jun/11/2019 16:05 (Moscow time).

The round will be rated for all Division 2 participants, yet any Division 1 participants are welcome to join us out of competition.

You will be given 6 problems and 2 hours to solve them. Score distribution will be announced later.

The listed handles below are contributors. Thank you for all who listed!

This is my first Codeforces contest ever. I hope everyone who will join this contest enjoy. Thank you!

WINNERS:

  1. Castor
  2. thecodinglizard
  3. puyu_liao
  4. UoA_Kanade
  5. abandonedw1
  6. average_frog_enjoyer
  7. orz_liuwei
  8. emengdeath
  9. ashutosh450
  10. hyfzbtrs

UPDATES:

  1. Let me spread the meme from McDic Minecraft Telegram group — Ggungah.
  2. Score distribution is 500-750-1250-2000-2250-2750.
  3. Editorial is available.
  4. Congratulations for the winners!
  5. I am sorry for weak systests for B and F. Sorry again.
  • Vote: I like it
  • +514
  • Vote: I do not like it

Comments Comments (219)
| Write comment?
»
6 years ago, # |
  Vote: I like it +8 Vote: I do not like it

Auto comment: topic has been updated by McDic (previous revision, new revision, compare).

→ Reply
»
6 years ago, # |
  Vote: I like it +53 Vote: I do not like it

Best of Luck for your first contest as a problemsetter.

→ Reply
»
6 years ago, # |
  Vote: I like it +88 Vote: I do not like it

Wa! A Korean round!

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

upvote if you believe there will be kpop tasks in his korean contest

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

    Listen to twice while solving twice problems.

    skill 1000

    → Reply
    • »
      »
      »
      6 years ago, # ^ |
        Vote: I like it +19 Vote: I do not like it

      listen to twice twice while solving twice problems twice.

      skills 1000000007

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

Hit you with that ddu-du ddu-du du~

→ Reply
»
6 years ago, # |
  Vote: I like it +23 Vote: I do not like it

I wish everyone high rating!

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

    Excellent tester for Excllent Contest ㅇㅅㅇ

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

Korean round will be amazing!!!Oh my my my, oh my my my! I've waited all my life. Oh my my my, oh my my my! Looking for something right:)

→ Reply
»
6 years ago, # |
  Vote: I like it +164 Vote: I do not like it

Why Hello is 안녕하세요 but Codeforces is 코드포스 which is shorter than Hello?

→ Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +60 Vote: I do not like it

    Also thought how difficult is it to write just "Hello", just unbelievable

    → Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +58 Vote: I do not like it

    That's not even a Hello.

    It's a Hi. XD!

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

      The other side is that Hi is longer than Hello! xD

      여보세요 : Hello

      안녕하세요 : Hi

      Google Translate

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

        And 'Hello' can be used as both '여보세요' and '안녕하셰요' in my country, so It is also able to say the length of 'Hello' and 'Hi' is equal. :)

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

        → Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +25 Vote: I do not like it

    I have always wondered how Chinese/Korean people write things

    → Reply
    • »
      »
      »
      6 years ago, # ^ |
      ← Rev. 2   Vote: I like it +34 Vote: I do not like it

      That's an art :D

      (However I have not mastered it yet. T_T)

      → Reply
    • »
      »
      »
      6 years ago, # ^ |
        Vote: I like it +93 Vote: I do not like it

      It is actually very simple. We have these Oriental supernatural psychic abilities to inscribe complex letters into paper without using hands.

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

      I wonder how Arabs too

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

        Nope writing Arabic is easy.Arabic alphabets are simple in shape.

        → Reply
      • »
        »
        »
        »
        6 years ago, # ^ |
          Vote: I like it +2 Vote: I do not like it

        No, I'm Iranian and our font, Persian or Farsi is like Arabic. I think it is easy. :D

        Maybe these different opinions are because of different viewpoints. For us Korean or Chinese are hard to understand. But now I see that you think Arabic is difficult. Because we all are used to our own languages and other ones seem strange. But the most important think is that all languages are beautiful. :D

        Sorry for my bad English. :D

        Btw do you Korean think your language is hard? Maybe I'm wrong.

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

          Though I write Chinese since I born, I still think writing it is a exhausting job, lol.

          → Reply
        • »
          »
          »
          »
          »
          6 years ago, # ^ |
            Vote: I like it +39 Vote: I do not like it

          Korean letter seems scary because one syllable is cracked into a single letter. However, it's actually a composition of consonant letters (ㄱㄴㄷㄹㅁㅂㅅㅇㅈㅊㅋㅍㅌㅎ) and vowel letters (ㅏㅑㅓㅕㅗㅛㅜㅠㅡㅣ). So while there are 11172 Korean letters, you only have to remember 24 simple letters- after then you can write all of them!

          Korean people are proud of their language, and we have a "language day" which recently became a holiday. I also think this unique system makes pronunciation much clearer and complete. However, I'm not sure if it's easy, because "easy language" and "easy letters" are a different matter, and "smart letters" and "easy letters" also are. It's my mother tongue, so at least I'm not the one to judge.

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

    Technically it's Annyeonghaseyo XD

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

    let's hope problems statements are long in Korean

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

    Well, if you use hanja honyong(漢字混用) to write 안녕하세요, the meaning of the phrase would be clearer (especially for Chinese). 안녕하세요=安寧하세요, it's asking if someone is free from worry. And, 코드포스=Kodeuposeu. This word is just a transliteration.

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

Waa~~ It will be Good Good Round~~ :)

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

korean round <3

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

It will be good round :D

→ Reply
»
6 years ago, # |
  Vote: I like it -6 Vote: I do not like it

How does it feel to have div2 after div3?

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

BTS brought me here!!

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

i hope there will be short questions !

→ Reply
»
6 years ago, # |
← Rev. 4   Vote: I like it -37 Vote: I do not like it

Apologize

→ Reply
»
6 years ago, # |
← Rev. 2   Vote: I like it +57 Vote: I do not like it

"...Thank you all who listed!:
- myself, arsijo
- myself
- arisjo
- tester — [some testers and myself]
- Mike"
tm McDic

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

Finally your round has arrived! Congrats! :D

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

The contest has extra-registration?

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

I hope a once wins your round :D

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

Unusual time for the contest, again

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

I wish it will be a great contest . Thanks for this Effort

→ Reply
»
6 years ago, # |
  Vote: I like it +40 Vote: I do not like it

... and who is the mother? did cf and polygon got born by bipartition?

→ Reply
»
6 years ago, # |
  Vote: I like it +19 Vote: I do not like it

크으.. 국뽕에 취한다.. Cheer up McDic !

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

I want to do last contest as a Specialist. -> Blue

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

    Focus on the problems and worry less about your ratings, it will automatically follow :)
    All the best!

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

    Deeply immersed by your curve :D

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

      Sorry to say, My C failed due to my minor mistake.

      Hurt me a lot.

      I gave too much effort into C.

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

      I think I will miss by +1 rating for becoming blue.

      → Reply
»
6 years ago, # |
  Vote: I like it +14 Vote: I do not like it

sees a codeforces round
Me: Codeforces round yay!
notices it's korean
Me: Codeuposeu round assa!

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

BTS bring me here

→ Reply
»
6 years ago, # |
  Vote: I like it -14 Vote: I do not like it

Is it rated up to 2100 rating like many other div2 contests?

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

Auto comment: topic has been updated by McDic (previous revision, new revision, compare).

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

Maybe the reason for the unusual time of the contest is Iran vs South Korea soccer match!

→ Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +58 Vote: I do not like it

    Or maybe Korean football players want to participate in their contest (;

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

Let me fly up to Purple on gookbbong round~~~~~~~~

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

Do you guys think doing a contest after anesthesia is a crazy idea?

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

    Yes, it is a crazy idea

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

      Well let's see how much I can get negative rating.

      → Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    i think it will be a great idea for me ,i won't feel the pain of my rating not increasing.

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

    Guys, don't try this or you will end up competing with half-closed eyes xD

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

퍼플가게해주세요...(Let me go to Purple this round)

→ Reply
»
6 years ago, # |
  Vote: I like it +53 Vote: I do not like it

Hmm. Why does nowadays always 6 problems? Is this only fast coding?

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

https://t.me/mcdic_ch

If anyone needed link to his minecraft telegram channel...

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

    That channel is not used for a long time.. lol. I have active chat group now.

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

      That is all what I found, sorry :D

      So share your active chat group!

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

It seems that I haven't got the ability to solve problem D as it scored 2000. (smog

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

Seeing the score distribution , i guess it is (speed + implementation) contest.

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

hi team :)

is the contest rated for div 3?

→ Reply
»
6 years ago, # |
← Rev. 2   Vote: I like it +57 Vote: I do not like it

That's why I love $$$ $$$ ̶M̶a̶t̶h̶f̶o̶r̶c̶e̶s Codeforces

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

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

What an amazing implementation contest!

→ Reply
»
6 years ago, # |
  Vote: I like it +13 Vote: I do not like it

In D why answer is not center of tree ?

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

    check a look:

    4

    1 2

    2 3

    3 4

    → Reply
  • »
    »
    6 years ago, # ^ |
    ← Rev. 3   Vote: I like it +8 Vote: I do not like it

    Try this case:

    8
2 1
1 3
3 4
4 5
1 6
6 7
7 8

    The only answer is $$$2$$$.

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

      so if the answer is not the center, then it must be one of the leaves right ? How to check that ?

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

        Suppose $$$v$$$ is not a center and not a leaf, then there are two leaves $$$l$$$ and $$$m$$$ at different distances from $$$v$$$ (suppose $$$l$$$ is closer). Consider the vertices at the same distance from $$$v$$$ as $$$l$$$ and notice that some of them are not leaves.

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

          Ok thanks but I know how to prove that. What I want to ask is that if it is not the center, how could we find the leave which is the answer ?

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

        I tried to find centroid on slightly modified graph(I deleted chains starting from leaf nodes) I was late for about 30 sec to submit

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

How to approch E ?

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

    The powers of f3, f2, f1 were terms of different tribonacci sequences with different first numbers. I couldnt figure out the sequence of powers of c, and it was also not there in OEIS :(

    Matrix Exponentiation is must, but couldnt figure out the matrix for c :'(

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

      Yeah, same ... wasn't able to figure out powers of c. Didn't know about OEIS though. Thanks for that :D

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

        If you make $$$n=n-3$$$, then powers of c would be $$$2*\sum_{i=1}^n i = \frac{ n*(n+1) } {2}$$$

        → Reply
    • »
      »
      »
      6 years ago, # ^ |
      ← Rev. 2   Vote: I like it +3 Vote: I do not like it

      You could reduce the problem to solving $$$G_{x} = G_{x-1}*G_{x-2}*G_{x-3}$$$, if you take $$$G_{x} = c^x F_{x}$$$. But, I couldn't see the fibonacci thing lol. Maybe we should have given the contest together xD.

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

      Power for c was (n-2)*(n-3) using summation of AP formed: 2*(1+2+....(n-3)).

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

    The answer is some power of $$$f_1,f_2,f_3,c$$$

    To deal with the power of $$$f_1,f_2,f_3$$$ it is a three-term recursion.(Fibonacci number is a two-term one). It can be rewritten in matrix form, and use fast power for large power.

    To deal with $$$c$$$ it is 2* A062544 in OEIS? It has a closed matrix form and solve it similar to the first one.

    Update 1 : Check tutorial/other stuff for better calculation of c

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

    Let g(x) = logc(f(x)) and h(x) = g(x) + x.

    The original equation becomes h(x) = h(x-1) + h(x-2) + h(x-3).

    After this, the problem could be solved by matrix power mod.

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

      exponent " c " can be attached with f(X) to make it g(x) = (c^x)*f(x) ;

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

        Yes. They look equivalent. I guess I am just not very comfortable with exponents.

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

          I looked at your code https://codeforces.net/contest/1182/submission/55452776

          However, I was unable to understand the last 3 lines : 

          ans = mul(ans, pow_mod(C, (3 * ll(a) + 2 * b + c) % (MOD - 1)));
n %= (MOD - 1);
ans = mul(ans, pow_mod(C, (MOD - 2) * n % (MOD - 1)));

          It would be great if someone could explain them!

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

            Suppose after solving $$$h_x = h_{x-1} + h_{x-2} + h_{x-3}$$$ we end up with something like: $$$h_n = u\cdot h_3 + v\cdot h_2 + w\cdot h_1$$$.

            Therefore, $$$f_n = f_{3}^{u} \cdot f_2^{v} \cdot f_1^{w} \cdot C^{3u + 2v + w} \cdot C^{-n}$$$

            By Fermat's little theorem, we can take the reminder of the exponents mod $$$(MOD-1)$$$ to simplify the calculation.

            I hope this explains.

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

how to solve C ??

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

    sorting first by the number of vowels, then alphabetically, on the one that ends, and then we create two arrays and run by the sorted, we look at the neighbors, if the letters are 2 words, then we sort again and see if the number of letters is equal, then it is 1 word. sorry, i don't know English very well.

    → Reply
»
6 years ago, # |
  Vote: I like it +48 Vote: I do not like it

Shitty fast typing contest.

→ Reply
»
6 years ago, # |
  Vote: I like it +55 Vote: I do not like it

I think in problem C finding m is enough and printing lyrics just makes problem complicated.

→ Reply
»
6 years ago, # |
  Vote: I like it -6 Vote: I do not like it

How to solve E ??

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

Any idea about pretest 16 in C? Is this logic wrong: For a given word,check if there is a word with same vowel count and same last vowel. If it isn't there,Try to check if there's something with same vowel count.

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

    case: 4 a e e u

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

      holy crap. i should have run a pass first for finding all pairs with both vowel count and last vowel same,instead of doing both at the same time. changed that and your TC passes. Is this logic right? ^

      → Reply
»
6 years ago, # |
  Vote: I like it +41 Vote: I do not like it

C was devastating :))

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

Many submission will fail at problem B, i did 4 hacks and was close to 5th.

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

    some hacks were

    single dot (.)

    single (*)

    and (*****)

    and

    .*.

    **.

    .*.

    and

    5 10

    ..........

    ..*.......

    .******.*.

    ..*.......

    ..........

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

      And what the answers? it should be NO for all?

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

    Predicted OMG ^^

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

      hahaa.. even i went to hacking after first 3 problems as it was very hard to solved the remaining in remaining time. i did 4 hacks, submitted invalid input for 5th otherwise it would be 5. LOLOL..

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

Auto comment: topic has been updated by McDic (previous revision, new revision, compare).

→ Reply
»
6 years ago, # |
  Vote: I like it +114 Vote: I do not like it

→ Reply
»
6 years ago, # |
← Rev. 2   Vote: I like it +81 Vote: I do not like it

A: quite nice

B: cases

C: probably some cases too, didn't think of this task

D: quite an easy idea I think, shitty to implement

E: maths

F: maths

I'm sorry, but I didn't find any of these tasks entartaining, very bad problem set (for me).

→ Reply
  • »
    »
    6 years ago, # ^ |
    ← Rev. 3   Vote: I like it +6 Vote: I do not like it

    good analysis, though d was good. i think the problems were not learning oriented. I was expecting this, as it has became too common in chinese and korean rounds. even dp problems are like they r picked from some maths olympiad books.

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

    I think D is so hard (sad)

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

      Is a nice problem though. I'm still thinking

      → Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +13 Vote: I do not like it

    first submit D, then talk! you made 9 attempts for D and still couldn't solve it! still a bad problem set FOR YOU?

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

my code shows this output on C Idk why
2
that first
the this
mcdics about
wow round
edit:never mind stupid erase mistake

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

RIP B

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

B = hackforces

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

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

If honestly I don't understand. Pretests must be weak or this was just occasionally? I mean hacks like '.' and '*' and test 23 and so on. I understand that it is my fault but all in all pretests was too weak.

→ Reply
  • »
    »
    6 years ago, # ^ |
    ← Rev. 2   Vote: I like it +3 Vote: I do not like it

    I asked them in the contest time about test only a * and they answered me its a invalid +, so if you were in doubt about this, you could have asked, even tho the pretest should have this test, I think.

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

How to calculate power of c in question E ?

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

    I think it is 2^(n-2) -2

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

      For n=8 I calculated power of c as 60 and 116 for n=9

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

    According to me power of c was (n-2)*(n-3). I wasn't able to calculate powers of f2,f3 in time.Is power of c correct??

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

https://codeforces.net/contest/1182/submission/55446726

O(TQ) solution passed in 31 ms

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

Seems like I have to give 2-3 contests to just come back to my original rating now :(

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

it`s a time to be expert ^^

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

E and F was math problem. I think that F was pretty good, because there isn't many Trigonometry Problems

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

What is the test case 23 in div 2 B . My submission is fail on it test case 23 https://codeforces.net/contest/1182/submission/55452743

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

    Only one "*"

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

      There should be atleast" +" symbol it neans all upward down left right and middle should be filled..so how single star??

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

        A "+" shape is described below:

        A "+" shape has one center nonempty cell. There should be some (at least one) consecutive non-empty cells in each direction (left, right, up, down) from the center. In other words, there should be a ray in each direction. All other cells are empty. Find out if the given picture has single "+" shape.

        This is what a + is, so, it s not obligated to have a + shape in the input, and that is why you have to code to find if there is only one + shape in the input, are you kidding me?

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

          Alteast one is each side is written...so how single star?

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

            dude, can you talk private? i wana help you

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

            Even I coded the same logic as you. It will fail this case:-

            5 3

            .*.

            ***

            .*.

            ...

            .*.

            Answer should be NO but your code will print YES

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

Can someone check what's wrong in this solution for C? https://codeforces.net/contest/1182/submission/55451525

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

In problem E, I am facing a doubt: I initially thought that I can condense the problem to the powers of f1,f2 and f3(ignore the c power for now). The powers of f1,f2 and f3 will be the nth, (n-1)th and (n-2)th term of Tribonacci sequence. But the powers will be in form of mod(10e9+7). As we know (a^b)mod M != (a^(b%M))%M ex: a=2,b=5,M=3, how do i effectively get the answer?

→ Reply
»
6 years ago, # |
← Rev. 2   Vote: I like it +3 Vote: I do not like it

For test case 35 of problem B My compiler gave a 'NO' but codeforces custom invocation is giving 'YES' and I think I handled the case on which it is failing.

here is my submission:

Can someone please tell me why is this happenning?

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

    The problem is in your last two loops, it accesses invalid address
    for(ll j=0; j<=m; j++) ( it should be j<m )

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

Can you check my idea for solving "E"? In my point of View we can calculate degrees of F1, F2, F3, C F1's degree is Fib(n)

F2's degree calculates by: F(1) = 1; F(2) = 2; F(3) = 3; F(n) = F(n — 1) + F(n — 2) + F(n — 3) F2's degree equal to F(n);

F3's degree calculates by: F(1) = 1; F(2) = 2; F(3) = 6; F(n) = F(n — 1) + F(n — 2) + F(n — 3) F3's degree equal to F(n);

C's degree calculates by: F(1) = 2; F(2) = 6; F(3) = 14; F(n) = F(n — 1) + F(n — 2) + F(n — 3) C's degree equal to F(n) + (2 * n — 6)

Is my solution right? I got problem with Fast Computing "Tribonachi's"

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

anyone can help me ? my code in problem B get wrong on test 23 But i test it locally and i get it OK

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

    With what?

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

    Test 23 has only one "*", are you outputing "NO"?

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

      I copy test 23 and run in my code and get "NO"

      → Reply
  • »
    »
    6 years ago, # ^ |
    ← Rev. 3   Vote: I like it +1 Vote: I do not like it

    case: 5 5

    .......*..*.*.*..*.......

    answer is "NO",but you get "YES".

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

      5 5 ..... ..*.. ..*.. ..*.. .....

      your test is ? if it is , i test it locally and get it yes

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

        try this one : ans will be no bt ur sol is giving ys.

        5 10

        ..........

        ..*.......

        .******.*.

        ..*.......

        ..........

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

Congratulation to puyu_liao

→ Reply
»
6 years ago, # |
  Vote: I like it -24 Vote: I do not like it

Make it unrated

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

    Its impossible. There weren`t any technical problems on CF during the round

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

For E,I have an idea.

It's easy to calculate the power of f1,f2 and f3.I have a way to calculate the power of c easily. The transfer matrix:

0 0 1 0 0

1 0 1 0 0

0 1 1 0 0

0 0 1 1 0

0 0 0 1 1

By using this,we can change [a,b,c,d,e] into [b,c,a+b+c+d,d+e,e]

The formula of the power of c is f[i]=f[i-1]+f[i-2]+f[i-3]+2*i-6

Let a=f[i-2],b=f[i-1],c=f[i],d=2*i-6,e=2

So now we can transfer it.

The initial matrix is [0,0,0,2,2],because f[1]=f1*(c^0),f[2]=f2*(c^0),f[3]=f3*(c^0).

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

    And sorry for my poor English.

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

      Thank you, understood well enough.

      → Reply
»
6 years ago, # |
  Vote: I like it -23 Vote: I do not like it

It was what I worried about. If my country's users set problems for the first time and there was some factors that can be issue, next time my country's (other) users set second problems, people won't expect much.

→ Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +21 Vote: I do not like it

    For your information, I am not the first Korean problemsetter.

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

      I see. Anyway, because it's been a long time since there was Korean problemsetter, more prudence should have been.

      → Reply
      • »
        »
        »
        »
        6 years ago, # ^ |
          Vote: I like it +24 Vote: I do not like it

        Please don't care much about problemsetter's nationality. There are many good Korean problemsetters and I believe community care enough about them.

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

          your problem set was nice enough

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

            I, didn't emphasized the problems' quality. And the quality of these is good. The sad thing is weak pretests.

            → Reply
  • »
    »
    6 years ago, # ^ |
    ← Rev. 2   Vote: I like it +14 Vote: I do not like it

    ainta and .o. set the best Codeforces Round in the history of Codeforces ever, so it's OK.

    On a serious note, I think the round was nice. B is cool for Div2. D is quite interesting with strong pretests. Difficulty distributions are bit flawed, but it's fine if D/E was swapped, and you can see scoreboards anyway.

    (I actually didn't liked problem F, because one can just copypaste NAIPC 2019 D and play with some stupid binary search. but the model solution was easier, and I think it's not an issue for 99% of participants..)

    In the end, difficulty distributions are not something setter can guess correctly, and interesting problems are much more important. For every CF round, there is someone complaining about pretests and distributions, I just advise to ignore them :)

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

      I, also want to think that way, but since that contest was over before more than 4 years, and since that there was no contest in which Korean was main problemsetter, for users joined after that contest this was like the first Korean problemset contest. It is also true that there are still many chances.

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

Well balanced problem set, nice.

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

problem c: is it valid? this first wow i .

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

Can anyone provide me a clear explanation on D? I thought many things non of them worked properly/on-time.

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

Guys, what is the time complexity of rating changes calculation? Why does it take so long? Can't wait already =)

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

E can also be solved using Reeds Sloane Algorithm(extension of BM for non-prime modulo). Link

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

Test case is weak for problem C, there is no case present in the systests where no. of vowels of a string is more than 100000. I used that number as an array index in some part of my code, got AC even after I miss sized the array.

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

    Exactly. In my solution too I used an array of 100000 for storing the strings with number of vowels. I was sure that my solution would fail at system testing. I was shocked to see it passing. So yeah, Weak Test Cases For Problem C.

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

    I'm sorry about issue.

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

Anyone who can take a look at my solution for E? 55469911

I have no clue why it passed on small range input but failed on the bigger ones.

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

Attention!

Your solution 55457716 for the problem 1182C significantly coincides with solutions Athena_1111/55457716, Anti-Mirzayanov/55458879, gandhipaaji/55458903, shreyanshgeek_unofficial/55458966, Harsh_jiit/55459119, turtle407/55459150, kaptaan/55459742, firefox/55459961, shivansh100/55460142, Izanagi/55460447. Such a coincidence is a clear rules violation. Note that unintentional leakage is also a violation. For example, do not use ideone.com with the default settings (public access to your code). If you have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, write a comment to post about the round with all the details. More information can be found at http://codeforces.net/blog/entry/8790. Such violation of the rules may be the reason for blocking your account or other penalties. In case of repeated violations, your account may be blocked.

I just got this message. I want to clarify (especially for people who are not aware of that) that I was using the online compiler ideone.com (I was using it for the past 3 contests and nothing wrong had happened before) without knowing that apparently my code was public (I didn't even know that this feature exists). I have not copied the code of anyone!! You can check the timing ( MY SOLUTION WAS SUBMITTED FIRST & I AM 100% SURE AND RESPONSIBLE FOR MY WORDS). I have written every line of this code!!! I haven’t even used functions from any website. It really pains to receive this message in the first contest where I do well. What a luck!!!!!!! :/ Be just.

→ Reply
  • »
    »
    6 years ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    "I was using it for past 3 contests and nothing wrong had happened before"

    Good that it happened to you now. Now you will never use ideone.

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

      It is fine to use it if you have private mode enabled.

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

      Why aren't earliest submissions only accepted in case of plagiarism?

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

        Because someone can copy the code from ideone and submit it faster than the original author.

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

      True, I should've payed attention but it's unfair to be punished because of others' malevolence.

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

        The world is not fair.You may as well get used to it.

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

        You are getting punished for your carelessness as well.

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

Why was I skipped in Codeforces Round #566 (Div. 2), but counted rating.

HELP！HELP！HELP！

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

I wonder if there's a solution for D using tree hashing, which I tried but failed.

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

shit. load shedding caused my specialist dream.

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

stupid Solution for D:

There are two possible types of vertexes, corresponds with the statements of the task:
1. One of the leaves
2. Vertex in the "middle" of the tree.

If there is only 2 vertex -> answer 1
If there is only 2 leaves -> answer is one of them

First of all, let's run bfs from each of leaves, and mark all the vertexes with their depths.
(depth[leaf] = 0, depth["middle"] is the maximum). Now, if vertex with maximum depth is unique, lets check it.
After, we need find one vertex with degree greater then 2 (it is always exist because of quantity of the leaves). Run bfs2 from it.
////Let's define nearest vertex with degree greater then 2 for current vertex like a good.
In this bfs, we need mark all vertexes by the pairs = {distance(current vertex, good vertex), index of the good vertex}.
It easy to proof, that if answer is possible, than there is only one leaf with unique pair {distance to its good vertex, quantity of leaves that correspond for this good vertex}. Now we just need to check this leaf.
code: 55487910

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

Why is my code for E giving wa on test case 5?

Got the error ignore.

→ Reply
»
6 years ago, # |
  Vote: I like it +19 Vote: I do not like it

weak tests for D
test
9
1 2
2 3
3 4
4 5
2 6
4 7
3 8
8 9
answer should be 9
https://codeforces.net/contest/1182/submission/55494688 gets AC but it shows -1 for this case.

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

    OMG I am really sorry about that. I handled almost ten type of trees and it was not enough.. :(

    UPDATE: Added that test in data

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

    I added that data and rejudged your case. I will try to find the way to rejudge all other's unofficial submissions. Thank you.

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

Regarding question C during the contest I submitted first one Then I found a small mistake and changed it to second one. If you compare both submissions the change was a variable n for a constant value. It was accepted, but then just out of curiousity I resubmitted my first submission third one you can compare it with my first one and it is literally the same, and I got AC with this.

However this is clearly wrong I mean you can test it with a small case ( 4 aaaaa aaaaa aaaaa aaaaa) My first and third submissions return 0 which is wrong and my second one returned 1 which is correct. So I'm not complaining about the fact that I lost points by fixing something that was wrong but would have been accepted anyways, I'm just wondering maybe the test cases are really weak or not good enough.

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

    I am so sorry about it. I should try so many various selections...

    UPDATE: Added that test in data

    → Reply