Hello, Codeforces!
I'd like to invite you to Codeforces Round #297 (Div. 2). It'll be held on Thursday, March 26 at 19:30 MSK and as usual Div. 1 participants can join out of competition.
Great thanks to Maxim Akhmedov (Zlobober) for helping me preparing the contest, to Maria Belova (Delinur) for translating the statements into English, to Mike Mirzayanov (MikeMirzayanov) for the great Polygon platform and ideas of some problems and to my old friends Pavel Kholkin (HolkinPV), Ilya Los (IlyaLos), Vitaliy Kudasov (kuviman) and Arthur Svechnikov (ikar) for writing solutions.
The scoring distribution will be announced later. Good luck everyone!
UPD The scoring is smooth dynamic (with steps of 250 points). More information about this can be found here. Tasks will be arranged in order of ascending supposed difficulty.
UPD2 Competition completed! Thank you all!
UPD3 You can find editorial here.
UPD4 Congratulations to the winners!
hello, i have decided that i'll downvote every comment in this post for fun :)
Sure, then everyone who comments in this post will downvote you for fun :))
downvote Is interesting and helpful for get negative contribution :))
Everybody wants positive contribution as like as positive rating..but?
It' s funny. I wish you get more and more downvote
Blog upvotes: 145. Your comment downvotes: 154. See the diference!
Can moderators add an option to disable people from commenting who troll here? I am pretty sure people are here to learn and not to waste time on attention seekers.
Do not be so serious. If there are no fun over here it will be boring.
I enjoy funny comments as well but let's just agree that this guy's comment is pure crap.
Your last contest had nice problems.
Thank you for creating another contest.
I think you mean "translating into English"? :)
As I see that you are from Russia and the google translate of your blog in Russian gives "translating into English" too
Fixed.
The comment is hidden because of too negative feedback, click here to view it :))
It was good
good
good
good
Why does the registration close in less than 2 hours?
Edit: Fixed :)
:D .
Thanks for the contest . Hopefully it will be a great learning expirience for everybody.
to div1 users: please dont create new accounts :||
like you?...you are one of them
Scoring distribution?
Codeforces Round #297 (Div. 2) 297 which is divisible by 9; 2+9+7=18=1+8=9 which is also divisible by 9; 2+7=9 && 9 which is also div by 9; Have any problem of divisible by 9? Best of luck.
I have a doubt. If 2500 people out of 3000 solve A , 2400 solve B , then how many points will be allocated for A and B (lets assume no of Solutions for C,D,E is < B)
Thanks fcspartakm
Nice contest :)
The scores of problems was so low that hacking was important than solving problems...
Why????!!!??? :(
What is solution to problem C...it seems like simple task but I cannot pass Pretest 4
Just make right rectangles. The square would be bigger, if the side of rectangle would be bigger. Let's sort them! And after that you can use dinamic programming.
Does dp is really needed here? I've solved without it.
No DP is needed. Sort and then traverse backwards.
I had a strange problem during the contest, two times my default compilator changed from GNU C++ to GNU C (and I get two compilation errors :)). Did someone else noticed such thing too?
I had the same problem.
Yes, compilator changed from PyPy 3 to Python 3, but that change got me AC to problem B :) (It was TLE in PyPy, but same code got AC in Python)
Same here...
So will we have -100 because of two compilation errors?
No, compilation errors do not count.
Ok, thanks :)
Mine changed from GNU C to GNU C++ :)
Great contest! Thank you fcspartakm!
multiple account?
really??? then Sorry_dreamoon is probably duplicate too...
He is, but not dreamoon_love_AA's. And I think that Majid perfectly knows the answer to his question but it seems like he wants to be downvoted...
Could somebody give me a hint of how to approach D and E?
Edit: Nevermind, the editorial was posted surprisingly quick.
I see the most hacks are in problem B.
Can anyone tell us what's the hacking test case ?
It was just a big test(maxtest). Some people used std::reverse and the complexity of their codes was O(N^2).
Just TLE. We must not swap symbols in all substrings, because it gives O(n / 2 * m) orepations
Many people did a slow O(NM) solution, reverse all the segments.
Of course it's not passing for test case like:
aaaaa... 100000 1 1 1 ...
Pff, I'm so sad because I didn't figure out E ... :(
Update: Nooo, my C is wrong :( :( :(
Those hacks saved my a*s :D
Same here, my C got pretests wrong, because of integer overflow!
So I make up for it with lots of hacks :)
Why this test generator is wrong ? the only explanation for that is 1 space in the end of file, because this works well.
Why 1 space generates an invalid input?
Because it is an invalid input. Somebody may read using fread with a buffer(sometimes I do so) and when you see the size of the buffer, then you can generate a test with a lot of spaces in order to make his/her buffer overflow and hack him/her.
Problem C was so ill framed in English :/
791 ACs on C. Then why would this problem have 1000 points? Isn't that the general solve count for problem C in a typical CF round? -___-
WA during the contest : 10474140 AC after the contest with the same code : 10476119 Just put a #include in a comment Any explanation ?
"Wrong answer on hack 1"
Doesn't it mean weak cases?
If I was in other room ,the code would have passed system test ! It isn't fair
You mean that the solution didn't even pass the pretests or it passed them and then it was hacked?
Passed the pretests then it was hacked after that I wrote a new code and got Wrong answer on hack 1, after the contest I re-submitted the same code ( which was getting WA on hack 1 ) and got AC
i had the same problem before in another contest, the thing guys told me back then was that limits.h is somehow not supported but i dont know exactly whats wrong...
Problem A got accepted and limits.h was included
its strange... i think it would be more useful if you asked this in stackoverflow.com
Was the round Unrated? if not, when will the ratings be updated??
Soon tm
in problem C in the test case 4: 8 5 3 3 3 3 4 4 4 how correct ans is 25?
decrease 5, then construct (4,4,4,4) and (3,3,3,3)
Yes
4*4 + 3 * 3 = 16 + 9 = 25 ...
I know !
The five becomes a four and then 4-4-4-4 and 3-3-3-3 are correct rectangles :)
On C it wasn't particularly clear that multiple rectangles are being created... "Ilya decided to make a rectangle from the sticks" implies at least initially that there is only one rectangle. (Or maybe I just need to read more carefully)
Agree. Google translate does a better job:
"Ilya decided to make rectangles of the sticks."
I hope that the translators be more careful about the singular/plurals.
D was one of the most interesting problems i have ever seen. Too bad i took wa on #12 :(
Thanks who send to B with O(n^2) complexity
can anyone help me why this solution got WRONG ANSWER http://paste.ubuntu.com/10685457/
UPD : it's okay i got it now!!
Can anyone tell me why my C solution was skipped whereas the same code got accepted after the contest?
You have cheated.
With whom my code has been matched can u tell me??
http://codeforces.net/contest/525/submission/10464753
Guys, did I solve one or two problems?
One
I meant two
I'm afraid to seem impatient but when ratings will update?
http://codeforces.net/contest/525/standings/page/4 uwi's B is still judging, wtf?
And slycelote's A :D
is the contest unrated??
No. The ratings have been updated!
Would you mind putting " UPDX Contestants' rate changed" in the end of the post, when new rates apply?
I'm waiting for ratings...
Do they come tonight????
I am staying up all night just for looking at the rating update. When will it be updated???
Now :P
I cannot see the problems in the "PROBLEMSET".
Oh, I find them. But it is very strange that they are not listed in top.
This is the code used in Winner's C: http://codeforces.net/contest/525/submission/10463905 This is the code used in enesoncu's solution to another problem: http://codeforces.net/contest/436/submission/10422970
Doesn't it look very similar!
Can you tell me what is wrong with hacking using generator? I tried three times during this contest, but i have got Validator 'val.exe' returns exit code 3 [FAIL Expected EOLN (stdin)]
Probably this is connected with the fact that i have used std::endl? How to do it correctly? Should I use "\n" next time? Because I really could have done at least 2 hacks!
Thank you
Can you help me?
http://codeforces.net/contest/525/hacks/143414/test
Judge return this:
Validator 'val.exe' returns exit code 3 [FAIL Token parameter [name=s] equals to "/********...correspond to pattern "[a-z]{2,200000}" (stdin)]
I couldn't find any problems...
It seems you've submitted it as a test, not as a test generator
Thanks for interesting problems and weak pretests. There were nice opportunities to hack.
Could somebody please help me to interpret the following wrong answer on problem D:
Test: #12, time: 717 ms., memory: 4404 KB, exit code: 0, checker exit code: 1, verdict: WRONG_ANSWER
expected: '***..*......*...****.*****.*.....**.*******.******.*..***.***.**', found: '***..*......*...****.*****.*.....**.*******.******.*..***.***.**'
Both strings are identical, but still in some way the validation system seems not to like my string. Thanks in advance.
Maybe you print
'\0'
at the end of your answer? :Prather not, as the wrong answer is in test 12 in the 6th word. In such situation all preceding tests should also fail.
Thanks anyway. I am really puzzled with this error.
The line is actually 2000 characters long, but Codeforces displays this kind of error like
[some prefix]+"..."+[some suffix]
Thus, in your error, the "..." unfortunately looks like part of the line. The real error is somewhere in the middle :P