### gridnevvvit's blog

By gridnevvvit, 6 years ago, translation, ,

Hello!

A few hours later, on November 29th at 19:30 MSK, you are lucky to participate in Codeforces Round #216 for Div. 2 participants. Traditionally, Div. 1 participants can take part out of the competition.

Problems have been prepared by: Gridnev Vitaliy (gridnevvvit) and Los Ilya (IlyaLos).

We want to thank Gerald Agapov (Gerald) and Sergey Sukhov (Serega) for help in preparation of this round, Mary Belova (Delinur) for translation of statements, Michael Mirzayanov (MikeMirzayanov) for marvelous Codeforces and Polygon systems.

UPD1: Scoring will be next: 500, 1000, 1500, 2000, 2500.

UPD2: It was a misprint with scoring system, now it is correct.

UPD Contest finished, congratulations to winners!

Good Luck!

• +81

 » 6 years ago, # |   +21 Friday. And again, and again, and again. No problem, just discoursing :)
•  » » 6 years ago, # ^ |   +12 Hope This Round to be a bridge to be a Div1 for First Time ,Hope That!
•  » » » 6 years ago, # ^ |   -15
•  » » » 6 years ago, # ^ |   -48 Are you fucking kidding me !?
•  » » 6 years ago, # ^ |   +10 What do you mean by again? there hasn't been a contest on Friday since 25th of October! :D
•  » » » 6 years ago, # ^ |   0 I think what he means is there is no contest especially for DIV.1. :D
 » 6 years ago, # |   0 GL && HF!!! I hope this contest will be good for everyone!
 » 6 years ago, # |   +10 Why this blog is not on the Home page ?
 » 6 years ago, # | ← Rev. 3 →   -13
 » 6 years ago, # |   0 An empty contests list !! I hate that ...
•  » » 6 years ago, # ^ | ← Rev. 2 →   +3 Then do something about it! Prepare a contest! No-one gets better from your trash. Sorry.
 » 6 years ago, # |   +14 "Scoring will be next: 500, 1000, 1500, 2500, 2500."So another Div.2-Only contest where maximum 10 people will solve D and/or E? :)
•  » » 6 years ago, # ^ |   +3 misprint :) Scoring will be next: 500, 1000, 1500, 2000, 2500.
 » 6 years ago, # |   0 HF:)
 » 6 years ago, # |   +3 I thought there are more than 3000 programmers taking part in this contest~nice weekend~~&&HF
 » 6 years ago, # |   0 short statement hope .....
 » 6 years ago, # | ← Rev. 4 →   -22 gyfhgfh
 » 6 years ago, # |   -12 din't register soon enough. Can't participate :(
 » 6 years ago, # |   +1 Why isn't runtime error considered as a successfull hack?I tried and it says unsuccesfull hacking attempthowever it should have shown runtime error according to my machine
•  » » 6 years ago, # ^ |   +34 A program can behave differently on different machines. (On yours, it crashes, but it works fine here.) This happens sometimes, and that's why it's risky to hack on RE or TLE.
•  » » » 6 years ago, # ^ | ← Rev. 2 →   +1 There were some sure cases of division by zero. During hack people got caught, no problem. How the passed the final test. In which machine on earth found the result of division by zero successfully!!! please, Read this thread. http://codeforces.com/blog/entry/9771And very carefully look at the case 19 in the test!!! how can that pass and generate correct output by dividing by zero !!!!
•  » » » » 6 years ago, # ^ |   +1 1 1 1 1 1 1 was the case by the way.
•  » » 6 years ago, # ^ |   0 Depends on the reason of runtime error. If it's accessing an out-of-bounds element of array, the behaviour is indeed undefined. But if it's division by zero, the hack should be successful. This time, I hacked 4 people on this, and they used different programming languages: GNU C++, MS C++ and Python 2.
•  » » » 6 years ago, # ^ |   0 Actually it was modulus with 0something like 0%0.
 » 6 years ago, # |   +9 How solve problem E?
 » 6 years ago, # | ← Rev. 2 →   +12 Finally a contest with corner cases that are not covered in the pretests!I made 10 successful hacks with the case: 5 5 1 1000 100 100wohoooooooooooooo :D
•  » » 6 years ago, # ^ | ← Rev. 2 →   +11 I've made 6 successful hacks with 3 3 1 3 9 9, but firstly found, that my oun programm can't solve it :D After blocking the solution.. It was offensively..
•  » » 6 years ago, # ^ | ← Rev. 2 →   +11 I made 11 successful hacks with the case : 5 5 1 3 5 5I made 11th hack in last minute :)
•  » » » 6 years ago, # ^ | ← Rev. 4 →   -15 it's unfair :D Bon appetite!fucking carelessness !there isn't any test like your test in system test , is there ? :D
•  » » » » 6 years ago, # ^ |   +7 Why so serious. May b u will want leave the earth as soon as u read this http://codeforces.com/blog/entry/9771 Look at the test 19
 » 6 years ago, # | ← Rev. 2 →   +12 When I wanted to hack some solution, I found something really interesting... In GNU C++, this code doesn't get RE cout << 0/0 << endl; It works well and makes answer equal 0 and also this code int a; cin >> a; cout << 0/a << endl; if you get a = 0, the output is 0 but this code will get RE int a; cin >> a; cout << a/0 << endl; why??? Is this a bug or...
•  » » 6 years ago, # ^ | ← Rev. 2 →   0 I did the same thing.unsuccesful halking attempt.on users with (sall-sk)%(n-k).
•  » » 6 years ago, # ^ |   +22 Maybe compiler optimization of the form "0/anything==0"?
 » 6 years ago, # |   0 any1 knows why i have skipped on all 3 tasks
 » 6 years ago, # |   +15 What is the approach for solving problem D and E? Thanks in advance
 » 6 years ago, # |   -17 very very awful system test speed
•  » » 6 years ago, # ^ |   +21 Zazhralis'.
 » 6 years ago, # | ← Rev. 2 →   +20 After many rounds.....finally a TRICKY contest!
•  » » 6 years ago, # ^ |   0 Two consecutive tricky contests , last was one also full of hacks and failed system test.
 » 6 years ago, # |   +4 what's the algorithm for problem E? i tried to use Fenwick Tree(Binary Indexed Tree) but i couldn't figure out how to use it 8-|. i solved problem just for 1 point... but for couple of points :-?? can anybody give hints? it would be great!
 » 6 years ago, # |   +2 What was special about test 14 in problem C ?
•  » » 6 years ago, # ^ | ← Rev. 2 →   0 Do you try this case? 4 1 2 2 2 3 1 2 4 2Answer should be 1 4
•  » » » 6 years ago, # ^ |   0 My code gets it right
•  » » » » 16 months ago, # ^ |   0 How did you get around Test #14?
•  » » 5 months ago, # ^ |   0 Any update on this?I'm stuck to this for hours now :/
 » 6 years ago, # |   +10 Test 32 on D is the killer of reds (me too :D), what could it be about...My solution of E is as follows: sort the intervals by li; sort the points of all queries together and for each of them, remember all queries that include it. Now, process the points in that order; in a BIT, remember how many intervals whhich start before that point and end at position i after that point (remembering their endpoints in a set also helps remove those that end before it). Check all queries asking for the current point, and add to their answers the intervals which won't be counted for any later point of that query — that is, end before the next point of it (or infinity, if that point is the query's last), which is just a sum from the BIT. The query's next point can be found just by remembering a pointer to it and increasing it when necessary.
•  » » 6 years ago, # ^ | ← Rev. 2 →   0 Here's the simplified 32 test on D.3 2100 0 50Solutions that fail on 32 test do not find the way to kill all fools and output 4 while the correct answer is 5. The main idea behind this test is that if one alive fool remains in front of a suffix of alive fools with a gap between them and he kills the first fool from suffix and dies himself at the same time, it may produce one more answer.Here it looks like that:round 1: The second fool is shot. The other two are alive.round 2: Remaining fools shoot each other simultaneously.Solutions that do not consider this case get WA 32.
•  » » » 6 years ago, # ^ |   +9 I see, thanks. It really took a lot of casework, this one...
 » 6 years ago, # |   +4 I liked the problems. Thanks for the contest. :) Even though I think D might be a bit hard, I have no clue on how to solve it. Hopefully, the tutorial will be out soon!
 » 6 years ago, # |   +42 Problems statistics (official round participants only): Participants count: 2021 A | first: 00:02 | sent/passed/hacked: 1963/1774/26 B | first: 00:08 | sent/passed/hacked: 1665/816/239 C | first: 00:11 | sent/passed/hacked: 819/442/1 D | first: 00:33 | sent/passed/hacked: 45/15/0 E | first: 00:44 | sent/passed/hacked: 87/11/0 
•  » » 6 years ago, # ^ |   +5 can u share with us how u got this data? it might help during future contests. thanks!
•  » » » 6 years ago, # ^ | ← Rev. 2 →   +11 I've parsed contest standings pages content and aggregated data from cells using javascript. It's draft, and I plan to extend the script in order to provide more interesting information in a pleasant view :)
•  » » 6 years ago, # ^ |   0 Good idea.
 » 6 years ago, # |   +35 Standings :1- Dshovn : Registered 11 Hours ago2- WhitedarkWalker : Registered 15 Hours ago5- Ronnoc_2 : Registered 3 Days ago6- LinXinya : Registered 8 Hours ago7- MWaltz : Registered 10 Hours agoAll those newcomers are pretty good i think.
 » 6 years ago, # |   +2 Shouldn't it be allowed to lock unsolved problems in order to hack other guys' wrong solutions?
•  » » 6 years ago, # ^ |   +1 i dont know, that seems unfair to me
•  » » » 6 years ago, # ^ |   0 You may not know how to solve the problem in an acceptable time and memory bound, but you can still have corner cases that submitter may have not handle.
•  » » 6 years ago, # ^ | ← Rev. 2 →   +16 I don't think that's a good idea, some guy can just create new account, lock, look at other guy solution, and re-code it for his main account and you know what happen next. So I think it will increase the number of cheater since it's really easy to cheat.
•  » » » 6 years ago, # ^ |   0 Good point, the fact that hacks can be made during coding time is the problem, indeed.
 » 6 years ago, # |   0 I solved A in 8 minutes, but was stuck with B because of a bug, which I manage to find only after an hour. :(
 » 6 years ago, # |   +16 First time top 5 :)
 » 6 years ago, # |   0 are the tutorials posted ???
•  » » 6 years ago, # ^ |   0 yes, here they are.