HolkinPV's blog

Codeforces Round #249 (Div. 2)
By HolkinPV, 10 years ago, translation, In English

Hi all)

Tomorrow at usual time will be held regular Codeforces round #249 for Div.2 participants. Traditionally we invite Div.1 participants to take part out of the competition.

The problems were again prepared by authors Pavel Kholkin (HolkinPV) and Gerald Agapov (Gerald). As always, we express our gratitude to Michael Mirzayanov (MikeMirzayanov) for perfect Codeforces and Polygon systems and Mary Belova (Delinur) for translating the problems.

UPD: Score distribution will be standard — 500-1000-1500-2000-2500.

We wish all participants good luck, high rating and enjoyment of solving problems)

UPD2: the contest is over, we hope you enjoy it)

UPD3: link to editorial is already here)

UPD4: Congratulations to winners!:

1) JiangZemin_JiangHaha
2) Rafbill
3) Yukinoshita_Yukino
4) kuangbin9
5) spartacus

  • Vote: I like it
  • +132
  • Vote: I do not like it

Comments Comments (83)
| Write comment?
»
10 years ago, # |
  Vote: I like it +51 Vote: I do not like it

You have just prepared Codeforces Round 246 (Div. 2) and now three contests after again you!
I think that would be better if you prepared a both division contest instead of 2 Div2 s. These days there are too few Div1 contests.
Anyway, I'm a Div2 contestant.
Hope everyone high ratings. :-)

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

An quite important contest for me. Because this June 1st is my last Children' s Day ever:p

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

    I think that Round 250's statement may mention the Children's Day. :)

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

      exactly. But I mean when the system test finishes, it will be June 2ed( or almost) in China! Or I can name it the last rating-change chance.( but actually, I couldn't do well in the past 'important' ones... Crossing my fingers now:)

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

What does the polygon system do exactly? Does it have anything to do with polygons?

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

    Polygon is a system to make life easier to generate problem set with input and output and input validators and more...
    not related to geometry polygon
    Click here to see it

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

    In Russian 'polygon' aside from its geometry meaning also stands for a place where weapons or some vehicles can be demonstrated and tested.

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

Your 20th (Div. 2) only contests!!!

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

OFFTOP

Did you see the innovation in info pages? The highest ratings are now noted near current one and pointed in rating graphics! So, wish everybody increase this indicator! :)

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

I hope to leave March with my first "Back to green" , waiting too long for this moment

→ Reply
»
10 years ago, # |
← Rev. 4   Vote: I like it +42 Vote: I do not like it

Nice thing that you keep making contests constantly. You are one of my favourite authors ! Looking forward for the round!

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

GOOD LUCK!

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

You have wished us in such innovative way in your last 3 round announcement post...
All the images are also unique... :)
Nice to see that wishes....
Image Hosted At MyspaceGens

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

    did someone notice a "poke-ball" in above goodluck image!! :D

    hoping to have another good experience in the contest!!

    good luck everyone.

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

    that is our new feature)

    → Reply
»
10 years ago, # |
← Rev. 2   Vote: I like it -12 Vote: I do not like it

OFFTOP

just noticed that now your cf profile also shows what your maximum rating is :D

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

Will anyone suggest me to improve my skill. I feel very darkness about my programming skill, rating,etc.

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

    Train , train and train — said Petr — . You also need to have a mentor to tell you if you are training in the right or the wrong way , and find some company who will encourage you to train

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

    Don't be upset, if programming is your passion continue to do it. Some people can't even write simple "Hello world" program! You need just to believe in yourself and you will do anything!

    P.S Sorry for my bad English.

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

    I also felt very darkness before, but now I feel very confidence. Just persistence. :)

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

      I'm so sorry for thanking you too late. Actually all are my fault, I'm responsible for all. I'm so sorry. Infinitely numbered thanks to you all. But you see that my performances in all contests that I've participated. It's not only developing my skill, practicing, doing well etc. but also it's the fame of my country, my institution, my trainer(my senior brother), all. What can I do?

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

It's kinda funny to be coding in a village where people are mad at you for not looking after the farms.

P.S.: Don't misunderstand. This is not where I live.

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

The contest for today was about to begin at 7:30 pm as per written on the contests page.. But it has not started. What is its correct time?

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

    it's 7:30 PM in MSK Moscow time

    you can view the time in your region from here

    or you can just wait 1 hour and 15 minutes :)

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

    can't you see the countdown on the right?

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

45 minutes before contest!!

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

    checking winners-to-be of the round? :)

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

I registered for this and it won't let me submit.

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

    Its saying that I'm not registered.

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

      Do you see yourself in the registrants' list? If you don't, you aren't registered, and you can know it that way even before the contest starts.

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

Problem B he decided that the number is to small to be. I think it should be too small to be

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

    Pasha decided that the number is too small to BE)

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

I should have accepted the problem D. What a pity...

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

Wrong answer on pretest 5 ??? (Problem D)

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

    At least I'm not alone who has this problem. I kind of checked everything in my program where a bug could be. But it seems more likely that some bug caused WA rather than wrong solution idea.

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

      I 've found the bug: Assume our triangle is right-triangle at (x,y). If triangle is not "white" in length L, it could be "white" in length L+1.

      For example:

      4 4
0000
0101
0011
0111

      Strangely, I have not found the bug in last 90 minutes. And I found it ~10 minutes after contest ended.

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

        Here the answer is 8, isn't it?

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

          Why is 8? I found 7 :S

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

            and i only found 6 :P

            → Reply
          • »
            »
            »
            »
            »
            »
            10 years ago, # ^ |
              Vote: I like it +6 Vote: I do not like it 
            three 00, one 00, one 0 , one 000, one 0        
      0        0      00       0       00        
                                       0        

and one 0000    
        0 0    
        00    
        0    
     
total 8 triangles.
            → Reply
            • »
              »
              »
              »
              »
              »
              »
              10 years ago, # ^ |
              ← Rev. 2   Vote: I like it -6 Vote: I do not like it

              how can you find it? can you tell me please?

              UPD : why you so rude to me? I just wanna ask for solution :(

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

How can I see the result? Or wait until tomorrow? This is my first time using Codeforces. Thank you and sorry for my pool English.

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

That was some real fast system testing!

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

Someone please give a test case where this (Div2 B) solution fails. Can't wait till the system test gets over. Thanks.

EDIT: Nevermind, the system testing was fast and the test cases are now visible.

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

    similar to my initial solution 6746602

    failing case: a = 129, k = 2.
    correct answer: 912

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

thanks for fast system

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

So fast System Test! It is very good:)

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

quick system testing.... :)

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

I wonder why when I rewrote 6749499, let it run on "10 10 all zeroes" on the custom test, it gave TLE, but when I tried to hack it gave the right answer. Is the testing system for custom test and for hack tests completely different or just random?

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

Some minutes before the end of the contest I inadvertently locked problem C(my attempt was A and B only). I saw I did something wrong (variable assignment) and asked the judges to unlock the problem, as I had not seen anybody's code and no one had attempted to hack my solution. I got a NO answer. I understand the decision, however, wasn't my question fair? Isn't there a way for the contest setters to see whether someone has looked at somebody else's code? ... seconds after the judging ended, I resubmitted and got AC as I expected. Not to happy about judge's decision.

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

    Well, there's no reason why your question wouldn't be fair. That's to say, the judges' decision is fair as well :D

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

System testing is too fast Probably because of strong pretests... BTW nice problem set and a successful round overall.... :)

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

When will the rating change? Will it be a long time?

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

Another time a Div2 only contest and 410 unrated users with strange usernames...

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

    i understand ur annoyed about it, but u don't have to take a sword and cut your computer because of that! :D
    PS: i'm referring to ur profile pic! :P

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

    weird isn't !!!! the official winners are new users most of div2 rounds !!

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

Rate-up!^^)

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

Is it possible for problem setters to try the problems in Java before setting the time limit?

For problem C I got a "Time Limit Exceeded" in the contest.. Changed using "System.out.print" to using a StringBuffer after the contest and it passed.

Same thing happened last contest, I got a "Time Limit Exceeded" probably just reading the input (even though I use a BufferedReader).

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

My wrong algorithm code got accepted for problem A! Check detailed info in my blog: http://mirror.codeforces.com/blog/entry/12481

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

why did I get WA on the problem B tescase 40 if it gaves me the correct output running in my computer,please help. http://mirror.codeforces.com/contest/435/submission/6750836

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

    In this part of your code :

    if(b+1  > a.length())
    l=a.length();
else l=p+b+1;

    That you determine the maximum index l you can go forward and pick some characters,

    You have a problem when b+1 < a.length() but p+b+1 >= a.length() then you access somewhere in memory where you didn't initialize.

    This can cause run-time error or some unwanted value. Here there was a 'n'in judge system memory after your string characters , and you bring that in your string.

    quick fix : l=min(p+b+1,a.length())

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

good contest and good problemset. only thing missing was hacks.
hope to see this level of problems with a few more hacking chances in ur next round! :)

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

what's the meaning of "skipped"?

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

    Skipped means your solution was not judged probably because you submitted it twice or some other participant had the same solution.

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

Round Stats

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

this code gives WA answer on test 5 for problem C but in the test button it gives different answer for this test case ?? My submission

→ Reply