Nerevar's blog

By Nerevar, 6 years ago, translation, In English,

Greetings to the Codeforces community!

I'm glad to announce that we again decided to introduce a round based on one of the programming olympiads for schoolchidren in Saratov. This time it is a round for participants from Division II. Round will start at unusual time for Codeforces: 12:00 MSK.

The problems were prepared by MikeMirzayanov and me, while Fefer_Ivan and Gerald helped us with writing alternative solutions.

Members of the first division can participate out of competition, as usual.

Scoring distribution is standard: 500-1000-1500-2000-2500.

UPD: tutorial can be found here.

UPD 2: The model solution for problem E (unfortunately, there were only one model solution) was incorrect. But, the answers for all pretests were correct. After the round we fixed the solution. All submits for problem E were rejudged.

UPD 3: Results are final, ratings are updated.

 
 
 
 
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6 years ago, # |
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Why the contest is only for div 2?

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6 years ago, # |
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It is a contest for singles~~~~November 11th~ROUND 211...Monday...So many "one"!

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What's the meaning of schoolchildren? Which ages does it contain?

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    6 years ago, # ^ |
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    This olympiad is for students from 8th to 11th grades of Russian school.

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Hope will get some nice problems ...

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E was a nice problem.

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Happiness is

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Can someone give the approach to solve problem D : Rent Bike ? Thanks in advance...

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    6 years ago, # ^ |
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    • first make n equals to m : if (n>m) take only the richest m boys, if (n<m) take only the cheapest n prices.
    • use binary search to search r , store the total amount spent by boys s everytime you check the condition in binary search. The answer for s is the last true condition in binary search check (that is, the largest possible r we found).
    • To check the condition in binary search, check it greedily : let's say you want to check for the answer X, then choose X richest boys and X cheapest bikes. Pair them respectively and see if it's possible for those X boys to buy those X bikes.

    Sorry for my English :)

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Ohh , why did I sleep through this contest :( . It looks like I missed a cool codeforces round :) .

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can someone explain me the reason why this solution did not passed?

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    6 years ago, # ^ |
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    t+=s[0];
    t+=s[1];
    

    t contains 2 chars now, but in answer there is only one (s[0]).

    s[1] does not exist at all, actually, so that I wonder why it is not runtime error :)

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      6 years ago, # ^ |
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      and what will change then in string t after this? t is same as answer,

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        6 years ago, # ^ |
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        What is s[1] ? You think that it is empty?

        You read string in s, but its length is 1, so that you didn't determine what is s[1]. The only character will be written in s[0], so that s[1] is undetermined.

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      6 years ago, # ^ |
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      Thanks! My solution failed because of this too!

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      6 years ago, # ^ |
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      I think that s[s.size()]='\0', got AC using printf("%s",t.c_str()); 5066622

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Problems were very interesting. Thanks to Authors...!!!

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    6 years ago, # ^ |
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    Same thing happened to me! My Submission fails on test 15:

    Input
    zz
    Output
    zz
    Answer
    zz
    Checker comment
    wrong answer Result is not a subsequence: 'zz' not in 'zz'

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    6 years ago, # ^ |
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    it maybe due to this piece of code

    ans += s[0];
    ans += s[1];
    

    u are adding 2 characters to ans, when there is only one character in input.

    EDIT: but what i dont know is why this resulted in Wrong Answer rather than Runtime Error. also, i agree with you that the Checker Log is contradicting itself!

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      6 years ago, # ^ |
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      Yes. Thanks. It should add an extra '\0' to the output string. Removing it, it gets AC. But, I wonder why would an extra null cause checker program to fail.

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        6 years ago, # ^ |
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        printf("%c",'\0') or cout<<'\0' will print a space.

        string str(10,'\0');

        cout<<str; will print 10 spaces while printf will stop at the first '\0'.

        -- MS C++!

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.

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In problem B , I solved in notebook using val += h[i] — h[g]; and unknowingly missed the + sign during coding 5061002 ,as the pretest passed i did not go through the code once :(

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I got WA in Problem C (test 15) while my program gives the correct answer!

Here's my Submission

Can anyone tell me why this happened?

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    6 years ago, # ^ |
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    This part is causing the problem : ~~~~~ if(s[0] == s[1] && s[1] == s[2]){ index = 2; }else{ s1[2] = s[2]; index = 3; }

    ~~~~~

    For the given case "zz", s[2] does not exist, thereby the control goes to the else condition and index is set to 3. So you are actually printing extra space along with your answer, which is invalid.

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      6 years ago, # ^ |
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      in this case...s[2]='\0',it can't be printed...and the '\0'(0) is not the ' '(32)....in ascii...

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    6 years ago, # ^ |
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    yes, my bad ... :( it is '\0' and shouldn't be printed. So the reason which I gave you, regarding your control going to the else condition is correct, whereas you are printing '\0'. Thanks for correcting me mathlover :)

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Problem E is very nice, but nobody got E accepted during the contest... When will the solution be published?

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    6 years ago, # ^ |
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    It's weird that I and several people got the same output for test 20. Is there something tricky in the problem that we possibly misunderstood?

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      I just fixed the bug I had in contest and now I also get incorrect on test 20. Weird...

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How is the standings is computed? Through the submission is accepted, but the standings is so low:(. Can someone explain for me, 3kq.

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Can anyone tell.why my this solution failed? 5062164

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    6 years ago, # ^ |
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    Ok.Null charachter was the issue. But i want to know.Why did WA came on 52nd test case when i did not put null charachter in the Output string and printed using %s.

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Test: #6, time: 0 ms., memory: 792 KB, exit code: 0, checker exit code: 1, verdict: WRONG_ANSWER Input aaa Output aa Answer aa Checker Log wrong answer Result is not a subsequence: 'aa' not in 'aaa'

why aa is not in aaa?? http://codeforces.com/contest/363/submission/5062051

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This contest was much easier with comparison to the previous ones...

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    6 years ago, # ^ |
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    but the E... only one person ac it in the last minute...

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Please !!! Update the rating !!! :( Eagerly waiting for that .....

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How to get the test datas?

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while trying to submit solutions in practice for today's contest, i got a message saying "Practice is allowed only for finished and unfrozen contests".

can anybody help me with this? thanks.

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Interesting. Why am I the Candidate Master with rating 1699?

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    6 years ago, # ^ |
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    I'm Master with rating 1408 :) I think they rollback rating because of some problems related to problem "E"

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    6 years ago, # ^ |
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    It seems the rating change for this match has been reverted due to an issue of problem E,but they forgot to update the handle colour.....

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Can you provide an official information of whether the contest will be rated or less?

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When will we have the Final standings?

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The editorial for problem E seems like brute force...What a strong test server...

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This was my 100th rated contest on codeforces. After the contest, I have my highest score in an individual contest(4076) , my best rank in a contest (31), my highest rating so far (1742).

PS — How many people have 100+ contest on codeforces. Who has the highest number of matches? I know Egor with 111 rated contest. Anyone higher ?

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For problem C this submission failed whereas this submission got AC. But all i changed was nothing related to the failed test case in the first place. Any reason?