Hello Codeforces!
SlavicG and I are glad to invite you to Unofficial Div 4 Round #2. Which will take place this Wednesday at 14:35 UTC (The round is over now, but you can still participate virtually). The round will not be rated for any participants since it is unofficial.
Contest link: https://codeforces.me/gym/102873
You will be given six tasks and two hours to solve them. The problems were created and prepared by mesanu and SlavicG for users with a rating range from 0 to 1400 but anyone is welcome to participate in the round!
We want to thank everyone who was involved in the round preparation:
Errichto for thorough testing and publishing this round on the gym.
Also, after the contest Errichto will post videos about this contest and the responsibilities of a tester.
UPD: Videos are now up: Fixing A, Testing A, Testing the rest.
Brodicico for help with problems and testing the round.
And a huge thank you to the testers: Errichto, Monogon, galen_colin, gupta_samarth, arujbansal, Chihai_Ion and Grumpah .
MikeMirzayanov for Polygon and Codeforces platforms.
Even though the contest is unrated, we believe it is an excellent way of practice, especially for Div 4 users.
Remember, if you don't know how to solve one problem, look at others!
UPD 1: Registration available now!
UPD 2: Round is over! We hope you enjoyed the problems and congratulations to the winners!
UPD 3: Editorial is out!
Div. 4 winners:
Not Div.4 Winners:
First to solve each problem:
A: First: Valera_Grinenko
Div. 4 first: anuragdvd
B: First: Geothermal
Div. 4 first: Esdeath_1
C: First: Geothermal
Div. 4 first: Esdeath_1
D: First: Geothermal
Div. 4 first: RamPrabodhInduri
E: First: Geothermal
Div. 4 first: -deleted-
F: First: IgorI
Div. 4 first: sahaun
As a tester, the setters are holding me hostage and forcing me to make an "as a tester" comment.
As a setter you have fulfilled your goal, you're no longer needed.
As a father, you guys will regret forcing my son to use his super powers
We didn't force him, we asked him nicely :)
as a fellow tester, ....
You know the drill
As not a tester, the setters are not holding me hostage and forcing me to make an "as a not tester" comment. Good luck to all participating. May your cp girlfriends help you solve all the problems.
I recorded the process of testing this round and complaining about bad statements, weak tests, etc. I even told the authors to replace one problem because it was stupid. That was a few weeks ago and the contest is well-prepared now, so I recommend participating.
On a related note, I'm going to create a guide on how to properly test a problem, especially in Polygon. Implementing a correct solution is actually less important than checking the validator, going through sample test explanation, or stress-testing the main solution with brute force. We get so many testers in CF rounds nowadays but they usually just solve problems. That being said, testing by solving problems still helps a lot in many aspects like estimating the difficulty and choosing proper TL, so it's great that testers are so appreciated recently!
Sounds like a lecture I need to pay attention to XD. Thanks for all the work, I know from experience that testing a full round is a big time and effort commitment
Indeed, it takes a lot of time to plan the dumbest comment that maximizes contribution.
As the only cyan tester...
I would like to thank ssense, SlavicG, Errichto, AlexNeagu, Monogon, galen_colin, gupta_samarth, arujbansal, Chihai_Ion, Grumpah, MikeMyrzayanov for being orz.
Also for creating a div 4 round! I hope noob like me can win it!
mesanu SlavicG i think your Div.4 idea is very good. Wish we had regular Div.4 in Codeforces. It's very good practive for newbies like me (only 141 points at IATI Shumen Junior).
oi!
It's a great idea to have these rounds. Hope to see more like this in the future.
What is the range difficulty of rating of problems?
thank you so much for all who help to create this round for us.
That would be great for beginners :)
Hope to see more like this in the future
RZK_19 see this
How to win this? Strategy is required !
Solve Problems
ping, it starts in 5 minutes.
very long queue now , i m exiting from the contest . Sorry guys i hope it will be better next time
Div4 round too powerfulThe queue wasn't too bad. For me it was just a few minutes, which isn't ideal but it's workable.
Why exit, try the next one
Yeah guys after eating the dinner i did participated again and i solved 5 except E which i solved in no time after the contest . Good round . I am not a judge so an opinion is that it should have problems of little bit more difficulty like 200 ratings higher maybe 1600++ .
So you want a div 3 round?
Nice set of problems!
nah
Is it Div. 5?
It looks like div.5, but problems were good.
Problems were interesting with respect to div 4 :D Had fun! Thank You for this round.
Glad you had fun!
can anyone plz explain approach to f
Editorial is coming!
Actually,cant wait.well thank u .enjoyed the problemset.would love to have such contests more frequently.
Editorial is out!
Try for $$$\text{n mod 4 = 0}$$$.
well i have predicted a draw if(n%4==0); else if(n&1) bob wins; else alice wins;
I saw your code. Your logic is ok. But you missed the newline after
DrawandAlice.Sorry about the long queue. Something was wrong with the system at the beginning and nothing was being judged. When everything started working properly after half an hour or so, the waiting time was at some peaks around 5 minutes and that was my bad because we had a lot of tests. I should have predicted that there will be enough participants that testing time might be an issue. Sorry! But again, the first 30 minutes were about unlucky technical issues :(
It was extra annoying that there was some CF error and we couldn't make any public announcement. We wanted to at least say something like "We're sorry about a long queue, it should be fixed soon".
Here's a 1-hour recording of me fixing a badly prepared problem A, and explaining to authors what should be done better. Half of the video is about generating good tests so maybe it's more useful for problem setters rather than for testers. https://youtu.be/KnMOEiySz0Y
UPD
Initial testing of A: https://youtu.be/L6cb9IOv4cE
Testing of the whole round: https://youtu.be/I7AJtUcVoxw
Coming later: a guide for testers.
Hey, thank you for making this. This is a really nice resource for anyone who wants to set problems.
This should get more love. Can you post this as a separate blog?
I will spend some more time on this to create a list of tips, and then post it on CF as a blog.
In E statement said contain string t. It's not clear that as substring or subsequence and all the example work with two cases.
Sorry for the confusion.
I was trying to solve the subsequence problem all the time :( and that solution actually passed 14 test cases which made my belief even stronger
First time I am mentioned as a "winner" in a blog post, hopefully not the last one :D