By awoo, history, 2 years ago, translation,

Hello Codeforces!

Please notice the unusual time.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 or 7 problems and 2 hours to solve them.

The problems were invented and prepared by Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Also thanks to Neal neal Wu for testing.

Good luck to all the participants!

Our friends at Harbour.Space also have a message for you:

Hi Codeforces!

We would like to invite you to a very special webinar called Digital Lockdown: AI against COVID-19, by Sergey Gordeychik, director of our Cyber Security programme.

Sergey is CIO of Inception Institute of Artificial Intelligence, and former CTO at Kaspersky.

During this webinar, Sergey will share his expertise and insights on how AI is being used both positively and negatively, during the COVID-19 global pandemic. Tune in for some practical examples of how companies are using AI to innovate and disrupt during a time of crisis, exploring topics like Medical Imaging for CT analysis, diagnosis and mass surveillance.

Join us on Thursday, May 28th at 12h (BCN) to gain knowledge and deepen your understanding about how we can use AI to solve both operational and societal problems.

By participating in this 1hour webinar you will get a certificate of participation, a special digital gift from Sergey, and have the chance to win a FREE 3-week module at Harbour.Space University, depending on the availability and prerequisites of the course.

Reserve your spot now!

Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 square1001 8 294
2 Anadi 8 305
3 tfg 8 681
4 mhq 7 192
5 xay_naive 7 248

Congratulations to the best hackers:

Rank Competitor Hack Count
1 qwscaln 29:-2
2 Ankit 5
3 lvao-x 3:-1
4 the_redback 3:-1
5 WICK_ED 2:-1
142 successful hacks and 828 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

Problem Competitor Penalty
A fedoseev.timofey 0:02
B Ashishgup 0:03
C1 hitman623 0:04
C2 square1001 0:15
D Not-Afraid 0:10
E autumn_eel 0:17
F squarepants 0:47
G riantkb 0:37

UPD: Editorial is out

• +47

 » 2 years ago, # | ← Rev. 2 →   -80 Good Luck ..
•  » » 2 years ago, # ^ |   -121
•  » » » 2 years ago, # ^ |   +187 wow you reposted my meme
•  » » » » 2 years ago, # ^ |   +48 Penalty : downvotes
•  » » » » » 2 years ago, # ^ |   0 agree
•  » » » 2 years ago, # ^ | ← Rev. 2 →   -35 that not good
•  » » » 2 years ago, # ^ |   0 Problem D video editorial for N log^2 N approach: LinkProblem D video editorial for N log N approach using Binary Lifting on Fenwick trees: Link
•  » » » » 2 years ago, # ^ |   0 well explained
•  » » » » 2 years ago, # ^ |   0 NlogN approach with FenwickTree gets MLE with Java while the very same code gets AC in C++. :(
 » 2 years ago, # |   +46 Wow this is really a good time in the Philippines! We can finally experience to join a contest at 5PM
•  » » 2 years ago, # ^ |   +55 good for Chinese too
•  » » » 2 years ago, # ^ |   +49 6 am for brazilians lol
•  » » » » 2 years ago, # ^ |   +6 5:00am for cubans :'v
•  » » » » » 2 years ago, # ^ |   +16 2:30 for indian
•  » » » » » » 2 years ago, # ^ |   +3 now its 2:45 for indians :)
•  » » » » » » » 2 years ago, # ^ |   0 lol yes
•  » » » » » » » 2 years ago, # ^ |   +10 wow, 5 more minutes now, 2:50 pm IST
•  » » » » » » » » 2 years ago, # ^ |   +75 It's extending just like Lockdown LOL
•  » » » » » » » » 2 years ago, # ^ | ← Rev. 2 →   -8 True
•  » » » » » » » » » 2 years ago, # ^ |   0 What is happening
•  » » » » » » » » » 2 years ago, # ^ |   +9 3:20 am for El Salvador, Center American
•  » » » » » » 2 years ago, # ^ | ← Rev. 2 →   +3 well 2:45pm XD
•  » » » » » » » 2 years ago, # ^ |   0 whats going on
•  » » 2 years ago, # ^ |   +14 Its the time for afternoon nap for indians
•  » » » 2 years ago, # ^ |   +5 I have a bad feeling about this
•  » » » » 2 years ago, # ^ |   0 hope this round will not get cancelled
•  » » » 2 years ago, # ^ |   0 XD
 » 2 years ago, # |   0 Again! Unusual time.
 » 2 years ago, # |   +18 Codeforces is entertaining quite by regularly holding contests in Lockdown. I'm enjoying. What about you guys?
•  » » 2 years ago, # ^ |   0 its very good
 » 2 years ago, # |   -11 Good Luck & Have Fun!Hope the round will go smoothly like last round!
 » 2 years ago, # |   +135 awoo , MikeMirzayanov with all due respect , can you please reschedule the round to next day or during usual time since kickstart will start 5 minutes before this round will end . We can't code for 5 hours straight .
•  » » 2 years ago, # ^ |   +54 Did you make this account just to make comments?? I wonder what could be the psychology behind this o_O
•  » » » 2 years ago, # ^ |   +28 Making alt accs just to make comments help as it helps you to be the jerk you are without ruining your real reputation. Though this comment isn't exactly being a jerk.
•  » » » » 2 years ago, # ^ |   -27 You have my upvote.
•  » » » » » 2 years ago, # ^ |   -25 You have my downvote
•  » » » » » » 2 years ago, # ^ | ← Rev. 2 →   +56 — And My Sword— And My Bow— And My Axe
•  » » » » 2 years ago, # ^ |   +13 meeooow can you plz try to achieve 0 ranting I really really wanna know if it is possible or not
•  » » » » » 2 years ago, # ^ | ← Rev. 2 →   0 Yes it's possible, even negative rating is possible. The lowest rating right now is -41. Check the last page of ratings table
•  » » » » » 2 years ago, # ^ |   +10 yep. trying my best to reach -ve asap. Though there are quite a few of them who've reached this milestone before. :) It's "rating", and not "ranting" btw.
•  » » » » » 2 years ago, # ^ |   0 Ratings can also be negative.I've seen a few negative rated profiles.
•  » » » » 2 years ago, # ^ |   0 @meeooow pretty cool rating graph btw
•  » » » » » 2 years ago, # ^ |   +3 thanks :)
•  » » 2 years ago, # ^ |   +11 I like your contribution :P
•  » » 2 years ago, # ^ |   -13 Did you make a new Codeforces account to say this?
•  » » 2 years ago, # ^ |   +12 I agree. Yesterday's Round 643 was stressful too which affected the Codejam after it. I would hate to skip a codeforces round especially made by such good writers.
•  » » 2 years ago, # ^ | ← Rev. 3 →   0 :( .contest delayed by 10+5 minutes.Now 20 minutes of overlap .
•  » » » 2 years ago, # ^ |   0 5 more minutes. But why?
•  » » » 2 years ago, # ^ |   0 I'm pretty sure you can just close the tab and go to Kickstart.
•  » » » » 2 years ago, # ^ |   +1 Well, if you perform poorly in today's round that will affect your kickstart participation so it's not just about time.
•  » » 2 years ago, # ^ |   0 And now the constest is delayed by 15 minutes more. Not a pro coder that I can solve all here and then go for kickstart as well.
•  » » 2 years ago, # ^ |   0 Seems like they deliberately wanted the contests to overlap. The 15 minutes postpone just strengthens this hypothesis.
 » 2 years ago, # |   +24 Whatever time it is the participants always show up in large numbers. I'm proud of this community :)
 » 2 years ago, # |   +62 Hey, this will clash with Kickstart round C for the last 5 minutes of contest, could you please schedule it something like 10 minutes earlier?Thanks
 » 2 years ago, # |   +7 Back to back contests.. That's why I love codeforces.
 » 2 years ago, # |   -9 It's great that there are so many contests but why this unusual timings ??? It's just irritating.....Back to back unusual time contests !!! Oohhh no...
 » 2 years ago, # |   0 Does the hacking phase got any points? Or will it affect the rating?
•  » » 2 years ago, # ^ |   -15 Go google it kid.
•  » » 2 years ago, # ^ |   +10 No. Educational and div3,4 hacking phase hacking has no points.
 » 2 years ago, # |   +6 I have rarely seen unusual time in educational rounds. What is the reason for unusual time?
•  » » 2 years ago, # ^ | ← Rev. 2 →   +7 I am not very sure but as far as I know, the contest time depends on the availability of the setters/testers during the contest. So the reason might be the mutual time decided by the setters/testers as their available time. Someone correct me if I am wrong.EDIT: It seems one of the setters has already notified the reason. This contest is tied to a local contest in Saratov.
•  » » 2 years ago, # ^ |   0 IDKMaybe because of some other coding events(or contests)
•  » » » 2 years ago, # ^ |   +12 It is tied with a local contest in Saratov.
•  » » » » 2 years ago, # ^ |   0 thx
 » 2 years ago, # |   +33 I think it's clashing with Google Kickstart round C. Though just 5 minutes but still it matters
•  » » 2 years ago, # ^ |   0 There is no break between the two contests that is only problem, usual time would't have created this problem. At last it is up to problem setters, they have their reasons.
•  » » » 2 years ago, # ^ |   -10 Can someone help me with the problems of kickstart round C. Where can I find the editorial?
 » 2 years ago, # |   +1 Will it be easier than general codeforces round of div 2 ? (I have fewer experience about educational round )
•  » » 2 years ago, # ^ |   +12 I feel educational rounds slightly more difficult than regular div 2.But be sure to learn newer things.
•  » » 2 years ago, # ^ |   0 maybe harder cause its problems is from GCJ
•  » » 2 years ago, # ^ |   0 from my experiences the difficulty is pretty much similar. but the open hack phase introduces some new challenges for us
 » 2 years ago, # |   +3 This contest has a clash of 5 minutes with Kickstart Round C. It would be better if this contest gets preponed by 5 minutes or so.
 » 2 years ago, # |   +116
 » 2 years ago, # |   -41 I kindly ask newbies and pupils not to participate in this round, you are causing big queues. you are wasting time. Stop programing!!!
•  » » 2 years ago, # ^ |   0 Says the person with a 666 rating... :/ tbh probably an alt
•  » » » 2 years ago, # ^ |   0 This isn't person, this is satan
•  » » » » 2 years ago, # ^ |   0 satan is not as dumb as you are
•  » » 2 years ago, # ^ |   0
 » 2 years ago, # |   -16
•  » » 2 years ago, # ^ |   0 OMG Ice Cube is so cool cruisin' in this Impala
 » 2 years ago, # |   0 Respected awoo BledDest MikeMirzayanov vovuh sir,I want to bring it to your notice that today there were back to back codeforces contest and google codejam for many of us and tommorow also we are having google kickstart and educational round as well, but the problem tommorow is that both of the contest clashes. Today there was a gap of 25 minutes bectween the two but tommorow its -5 min i.e. it clashes with each other. Moreover there isn't any upcoming schedule (except kotlin heros) so it can easily be shifted on some other day. If you still think that contest should be organised tommorow then please give a gap of at least 30 minutes so that everyone could refresh and take part in second one with fresh and cool mind and sorry I am bit shy. Please ignore and forgive me if I am pointless.Thank you
 » 2 years ago, # |   0
•  » » 2 years ago, # ^ |   +108 STOP POSTING GOD DAMN NOT FUNNY MEMES. please.
•  » » » 2 years ago, # ^ |   +5 Ok thank you for your suggesion.
•  » » » » 2 years ago, # ^ |   +2 Sorry if it was so aggressive(i said please in the end :) ), its fine if you are trying to make people laugh.
•  » » » 2 years ago, # ^ |   +33 ITS FUNNY FOR ME. STOP BEING A TOXIC.
•  » » » » 2 years ago, # ^ | ← Rev. 2 →   -25 funny or not, it shouldn't be here.
•  » » 2 years ago, # ^ |   0 loll
 » 2 years ago, # |   +119 Unfortunately, we cannot shift the round time because it is tied to a local contest in Saratov.
•  » » 2 years ago, # ^ |   -36 RIP our concentration and brain. Thanks for letting us know
 » 2 years ago, # |   +146 Codeforces evolution ->2017 — Spamming "Is it rated?"2020 — Spamming unfunny memes
•  » » 2 years ago, # ^ |   +19 I feel it's my fault :P
•  » » » 2 years ago, # ^ |   +3 No bro you are the legendary grandmemer of codeforces ,soon you will be among the top contributors
•  » » » » 2 years ago, # ^ |   +13 Thx <3 but Nah I won't reach top contributors the higher your contribution is the harder it gets to gain more and I'm running out of memes
•  » » » » » 2 years ago, # ^ |   0 Ngl, I look out for that one single meme of yours in every contest announcement. They really make my day. :D
•  » » » » » » 2 years ago, # ^ |   +13 Thx ! you made my day with your comment <3
•  » » » » » » 2 years ago, # ^ |   +2 Why this feels so cheezy !!
 » 2 years ago, # |   +13 Kickstart -> Educational -> Atcoder. This is just usual Sunday !!!. what's the hurry ?
•  » » 2 years ago, # ^ |   +45 Chocobar its Educational->Kickstart->Atcoder yours one should fail system test as its not in sorted order
•  » » » 2 years ago, # ^ |   +6 for blues it's ok
•  » » » » 2 years ago, # ^ |   +3 Until it get hacked
•  » » » » 2 years ago, # ^ |   0 See what I said , now you are no longer blue. RIP ratings
•  » » » » » 2 years ago, # ^ |   0 i'll be blue again soon. :D
 » 2 years ago, # |   0 so should we just abandon last 5 minutes of this contest for kickstart ?
•  » » 2 years ago, # ^ |   +3 Last 15 mins*
•  » » » 2 years ago, # ^ |   0 20 ^_^
 » 2 years ago, # |   0 I love Educational Round <3
 » 2 years ago, # |   -42 Is it rated?
•  » » 2 years ago, # ^ |   0 It will be rated for the participants with rating lower than 2100
•  » » » 2 years ago, # ^ |   -38 Hence, I am rated, right?
 » 2 years ago, # |   0 How do I unregister from this round?
•  » » 2 years ago, # ^ |   +6 it will not matter if you have registered and you don't appear for round, the round will go unrated for you. :)
•  » » 2 years ago, # ^ |   0 go to https://codeforces.com/contestRegistrants/1354/friends/true and unregister
•  » » » 2 years ago, # ^ |   0 thank you :)
 » 2 years ago, # |   0 Nice contest time :)
•  » » 2 years ago, # ^ |   0 3 consecutive contests right?sorry for downvote
 » 2 years ago, # |   0 Finally, I didn't do codeforces in the early morning. This unusual time is too nice for me
 » 2 years ago, # |   +2 It's a good time for Chinese people, but it may not be good for other places :)
 » 2 years ago, # |   0 Should I skip this round for kickstart or should I give both. Any suggestions?
•  » » 2 years ago, # ^ | ← Rev. 2 →   +3 Maybe you should give up one , cuz there's an atcoder round in the evening(in Japan)
•  » » » 2 years ago, # ^ |   0 agree
•  » » » 2 years ago, # ^ |   0 Do you mean the Japanese online judge atcoder?
 » 2 years ago, # |   +4 Live epic upsolving after the round:https://youtu.be/SdwVz4qzhkY
•  » » 2 years ago, # ^ |   0 looking forward to this
 » 2 years ago, # | ← Rev. 2 →   0 Hey, how come no more non-Kotlin Heroes contests scheduled after this Educational round? (Like dang, many hours past the contest...)
 » 2 years ago, # |   +18 Just meme :-)
•  » » 2 years ago, # ^ | ← Rev. 2 →   +19 Lol! Underrated!
•  » » 2 years ago, # ^ |   +9 Nice creativity!
•  » » 2 years ago, # ^ |   +6 You forgot to include AtCoder Beginner Contest ))
•  » » » 2 years ago, # ^ |   +11 sorry bro, my bad :(
 » 2 years ago, # |   +5 I think codeforces community is trying to know which time is the best time for holding contest so we don't encounter any problems. I think it is the strategy to find the most suitable time.
 » 2 years ago, # | ← Rev. 2 →   -9 Is there any specific reason for UNUSUAL TIME or its just fun? :)
•  » » 2 years ago, # ^ |   0 Yeah, there is... Kickstart round C is scheduled to start at 11:00 UTC.
•  » » 2 years ago, # ^ |   0
•  » » 2 years ago, # ^ |   0 It is tied to a local contest in Saratov.
•  » » » 2 years ago, # ^ |   0 Now the Unusual Time is more unusual by extending it 10 minutes. LOL!
•  » » » » 2 years ago, # ^ |   0 Now the Unusual Time has crossed the limit of Unusual time. LOL!
 » 2 years ago, # |   +15 Hope this contest will have some graph and DS problems.
 » 2 years ago, # |   +3 Great time!! Thanks for arranging contests so frequently . Thanks in advance for the webinar.
 » 2 years ago, # |   -6 If possible, set the time in such way that it does not clashes with another contest.
 » 2 years ago, # |   0 A really good time for Chinese! We can enjoy the contests this weekend without staying up late.
 » 2 years ago, # |   -6 It's the first time I am sitting for contests back to back. Hope the results will be good.
 » 2 years ago, # |   -7 Less than 20k participants after a long time . Results of Kick start clash may be . Looking forward for an another interesting problemset .
 » 2 years ago, # |   -67 I thing, it's good time for Bangladeshi Muslims. Because, in evening, we have evening prayer and Ifter. And in night, we have night prayer with Salatut Tarawih. But, this time,most of us are free. By the way, thank you Codeforces.
•  » » 2 years ago, # ^ |   -7 Ever heard of something called as kickstart
 » 2 years ago, # |   -15 Contest Extended!
•  » » 2 years ago, # ^ |   +36 Actually it's postponed
•  » » » 2 years ago, # ^ |   +23 Ya Sorry for my poor English hope I will not repeat the mistake in future.
 » 2 years ago, # |   +194 The contest got delayed 10 minutes and now the overlap with Google Kickstart is 15 minutes
•  » » 2 years ago, # ^ |   +3 exactly ! sux :(
•  » » 2 years ago, # ^ |   +2 when is google kickstart
•  » » » 2 years ago, # ^ |   +22 Thats my boy!!!
•  » » » 2 years ago, # ^ |   0 https://codingcompetitions.withgoogle.com/kickstart/schedule Just after this contest ends :(.
•  » » 2 years ago, # ^ | ← Rev. 2 →   0 Deleted
•  » » » 2 years ago, # ^ |   +4 Actually there is already an option to unregister.
•  » » » 2 years ago, # ^ |   0 you can deregister by going to the list of registered participant , on the top it will be your name click on cross sign
•  » » 2 years ago, # ^ |   +4 I think now most of them will give the contest by fake id!
•  » » 2 years ago, # ^ |   0 Who knows, if it will be further extended due to long queue :)
•  » » 2 years ago, # ^ |   +3 It's 20 minutes overlap now. Way to go !
•  » » 2 years ago, # ^ |   0 Now it is 20 minutes overlapping with Google Kickstart.
 » 2 years ago, # |   +3 Delayed for 10 minutes.
•  » » 2 years ago, # ^ |   0 Reason?
 » 2 years ago, # |   +7 delayed :(
•  » » 2 years ago, # ^ |   0 Kick Start is in 2 hours. Lost 15 min:(.
•  » » 2 years ago, # ^ |   0 Why tho?
•  » » » 2 years ago, # ^ | ← Rev. 2 →   -6 No point in wasting 1 hour 45 minutes. I think I will give all to cf first then Kickstart.
 » 2 years ago, # |   -9 Delayed by 10 minutes!!!
•  » » 2 years ago, # ^ |   0 15
•  » » » 2 years ago, # ^ |   0 20!
 » 2 years ago, # |   0 The voltage increases... another ten minutes.
 » 2 years ago, # |   +8 what the hell is going on ??
 » 2 years ago, # |   +5 Damn it, it's getting even worse now we have to abandon last 15 minutes of this contest
•  » » 2 years ago, # ^ |   +19 Codeforces should have preponed this round or kept at 8:05, owing to know Kickstart's schedule. :)
•  » » » 2 years ago, # ^ |   0 Yeah very true
•  » » » 2 years ago, # ^ |   0 See bledest replied the reason why the didn't did so
 » 2 years ago, # |   0 Delayed 10 mins :)
•  » » 2 years ago, # ^ |   0 What the hell is going on ?? :(
 » 2 years ago, # | ← Rev. 2 →   +9 A penalty of 10 mins to everyone!! HAHA Another 5 mins! Congratulations
 » 2 years ago, # |   +4 Delayed by 10 mins : hope server is fine
 » 2 years ago, # |   +5 Now a 15 minute overlap with kickstart,rather than 5
 » 2 years ago, # |   +5 I don't think it's very sensible to further delay the contest with an overlap of 15 minutes with Kick-start (which is a fairly popular competition and has almost 10k+ participants this year..)
 » 2 years ago, # | ← Rev. 2 →   +68 Everyone said make it 5 min earlier. Boom you delay it by 10 min. People start worrying for Kickstart. Meanwhile Codeforces : "Here comes another 5 min, you guys just probably spamming"
•  » » 2 years ago, # ^ |   0 again delay!!
•  » » 2 years ago, # ^ |   +3 Let's start side by side with Kickstart, what say?
 » 2 years ago, # |   +7 let's hope this delay is not a sign of long queues during the contest
 » 2 years ago, # |   +7 Contest should be postponed.It directly overlaps with Google Kickstart 2020.
 » 2 years ago, # |   -24 15 minutes of kickstart already lost Can't you see awoo
 » 2 years ago, # |   +1 Google Kick Start! :(
 » 2 years ago, # |   +123
•  » » 2 years ago, # ^ |   0 And there's 5 minutes more!
 » 2 years ago, # |   +20 Is this a measure by the problem-setters to decrease their competitors in Kickstart? >.<
•  » » 2 years ago, # ^ |   0 In that case, people will do Kick Start instead of this contest.
•  » » » 2 years ago, # ^ |   0 I don't think so, Kickstart has it's prestige but to people who want rated contests, they might skip Kickstart(or join late).
 » 2 years ago, # |   +21 For the First time, a 100 minute contest! XD
•  » » 2 years ago, # ^ |   0 another 5 min delay
•  » » 2 years ago, # ^ |   0 5 More mins??
•  » » 2 years ago, # ^ |   0 ok so no one is going to participate now +5min more delay
•  » » 2 years ago, # ^ |   0 Another delay
•  » » 2 years ago, # ^ |   0 no..its still 2 hour contest
 » 2 years ago, # |   -6 Amazing.
 » 2 years ago, # |   -6 Another 5 mins....
 » 2 years ago, # |   0 again
 » 2 years ago, # |   0 yo come on xd
 » 2 years ago, # |   +39 okay now i am probably gonna take part in atcoder instead of kickstart (:
•  » » 2 years ago, # ^ |   0 As per my suggestion prefer kickstart as atcoder contest take place every sunday but not so frequent for kickstart
•  » » 2 years ago, # ^ |   0 Same ^_^
 » 2 years ago, # |   +4 Another 5 mins :(
•  » » 2 years ago, # ^ |   +8 THis has become irritating now...
•  » » 2 years ago, # ^ |   0 They dont even care to tell the reason of the delay.
 » 2 years ago, # |   +5 This is frustrating
 » 2 years ago, # |   +2 Now , i m not participating
•  » » 2 years ago, # ^ |   +3 Me too!
 » 2 years ago, # |   +9 Man, You guys are killing me. Delayed further by 5 Mins. Its a 20 min overlap now.
 » 2 years ago, # |   +11 Please make sure not to start to early ;)
 » 2 years ago, # |   +8 I am truly amazed by the arrangements.
 » 2 years ago, # |   0 WTF is happening. Again 5 min delay.
 » 2 years ago, # |   0 Why delayed again?
 » 2 years ago, # |   +5 JUST TELL ME THE FINAL TIME OF STARTING CONTEST. GETTING PRETTY ANNOYED BY CHANGING TIME.
 » 2 years ago, # |   +13 I want my 20 minutes back
 » 2 years ago, # |   0 I was already ready to go in, as here again the transfer for 5 minutes )
•  » » 2 years ago, # ^ |   +14 By using GP (infinite) 10+5+2.5....=20 so contest will have 20 minutes delay
 » 2 years ago, # |   +7 just forget about Kick Start
 » 2 years ago, # |   0 What's up with the delays?
 » 2 years ago, # |   0 Seems its a trap now :)
 » 2 years ago, # |   +12 Why are they playing with our feelings?
 » 2 years ago, # |   +5 my patience is giving up .
 » 2 years ago, # |   +6 What the hell is that,2 delays?
 » 2 years ago, # |   +3 The contest is delayed by 15 minutes, so now we have 20 minutes intersection with Kickstart. Tough spot to be in.
 » 2 years ago, # |   +1 Here we go again!
 » 2 years ago, # |   +5 10 minute delay had a bonus!
 » 2 years ago, # |   +22 Again Delayed! It hurts more than a breakup.
 » 2 years ago, # |   0 WTF dude! Please check your server and conduct this round after kick start....
 » 2 years ago, # |   +25 While(onClick("Start Contest") { startTime+=5; }
 » 2 years ago, # |   0 5 more minutes ?
 » 2 years ago, # |   0 1 is okay but 2 is a bit frustrating
 » 2 years ago, # |   0 Server in trouble?
 » 2 years ago, # |   +8 delay the round without notice is really uncomfortable...
 » 2 years ago, # |   0 Are you guys planning to delay it over and over so that it starts exactly at the same time as Kickstart?
 » 2 years ago, # |   +6 wtf???????
 » 2 years ago, # |   0 why is starting time getting postponed every 5 minutes?
 » 2 years ago, # |   0 I wonder what had happened to this round.
 » 2 years ago, # |   0 Now 20 min penalty woaah why cf ??
 » 2 years ago, # |   0 What should be the priority kickstart or codeforces ??
•  » » 2 years ago, # ^ |   0 That's exactly what the codeforces want.To pick the best platform for programming contests.
•  » » 2 years ago, # ^ |   0 Depends upon your comparator
 » 2 years ago, # |   0 Why are you extending the time again and again. I have been waiting for 30 minutes for this contest t begin.
 » 2 years ago, # |   0 why the contest is getting late???
•  » » 2 years ago, # ^ |   0 Could be technical issues or unclear problem statements.
 » 2 years ago, # |   +8 Now we'll get to see real CF fans
 » 2 years ago, # |   +3 Maybe they are waiting for 20K registrants.
 » 2 years ago, # |   0 Another 5 min, Hope clear statements !
 » 2 years ago, # |   0 delayforces /qiang
 » 2 years ago, # |   0 Now delay the contest to some other day THIS IS NOT DONE!!
 » 2 years ago, # |   +9 How to solve A?
•  » » 2 years ago, # ^ |   0 Just do binary search for the timefirst 10 min then 5 then 2 then 1glhf
 » 2 years ago, # |   0 why delay again !???
 » 2 years ago, # |   +5 When I say myself,**"Now we go",**then Suddenly I see 10 min left,and after 10 min ,again I boosted myself ,and again I see 5 min to go
 » 2 years ago, # |   0 I am getting a meme feeling
 » 2 years ago, # |   +61 Will they keep delaying it until unusual time becomes usual ?
 » 2 years ago, # |   0 I already ready for program but codeforce said please hold patient .
 » 2 years ago, # |   0 Will educational rounds have points for hacking??
•  » » 2 years ago, # ^ |   0 No
 » 2 years ago, # |   +12 Testing our patience? xD
 » 2 years ago, # |   0 Kickstart guys going to suffer
 » 2 years ago, # |   +7 Guys, don't mess with cf. They will add 5 minutes delay for each meme xD
 » 2 years ago, # |   0 a contest with 100 min xD (until kickstart begins)
 » 2 years ago, # |   0 Why has the contest been postponed two times?
 » 2 years ago, # |   +3 I am wondering how are you holding an onsite contest during the COVID-19 epidemic?
 » 2 years ago, # |   +14 UnusualtimeForces × DelayForces √
 » 2 years ago, # |   +8 delayforces :(
 » 2 years ago, # |   +3 Yet another 5 minutes extended.
 » 2 years ago, # |   0 They should either reduce the length of the contest for everyone or postpone the contest altogether (IMO).
 » 2 years ago, # |   0 Putinforces?
 » 2 years ago, # |   0 Is it rated?
 » 2 years ago, # |   0 10min+5min delay.Hope all goes well.
 » 2 years ago, # |   -18 No offense!! Participate in kickstart. Nothing is left with educational rounds :/
 » 2 years ago, # |   0 for(;time<=4:30;start_time+=5)time++;
 » 2 years ago, # |   0 If they add 5 min more, I'll wait 5 min more
 » 2 years ago, # |   0 SPEEDFORCES!!!
 » 2 years ago, # |   0 Time limit exceed in test case 3 in A problem :((
 » 2 years ago, # | ← Rev. 2 →   0 how to solve D? my q*lgn*lgn using binary indexed trees(bit) ofcourse times out :(UPD — my same code with cin cout passes?!
•  » » 2 years ago, # ^ |   0 you don't need binary search, traverse the BIT to find the answer ~810ms
•  » » » 2 years ago, # ^ |   0 And I kept getting Memory Limit exceeded for some reason!!
•  » » 2 years ago, # ^ |   0 Use binary jumps
•  » » 2 years ago, # ^ |   +23 Either fast descent on BIT or segment tree (in $\log n$), or the following:Suppose we are trying to find the minimum element in the resulting multiset. To do this, let's implement a function that counts the number of elements not exceeding $x$ in the resulting multiset in $O(n + q)$ as follows: if we distinguish only between elements greater than $x$ and not greater than $x$, we can maintain the multiset as two simple counters. To find $k$-th statistics, simply check that the number of elements $\le x$ is not less than $k$; if it is so, $k$-th statistics is not greater than $x$.That way, we can count the number of elements $\le x$ in $O(n + q)$, and to find the minimum element in the resulting multiset, we may binary search the first $x$ such that the number of elements $\le x$ is non-zero.
•  » » 2 years ago, # ^ |   +6 My q*log^2(n) luckily passed, please hack it https://codeforces.com/contest/1354/challenge/80496838
•  » » 2 years ago, # ^ |   0 I used binary search on Binary Indexed trees(BIT) and it passed. Here's my submission in Java 80546129
 » 2 years ago, # |   +14 How to solve C?
•  » » 2 years ago, # ^ | ← Rev. 7 →   0 I think $\cot(\pi/n)$ works for C1.
•  » » 2 years ago, # ^ |   0 For C1,i solved it by finding the inradius of the polygon multiplied by 2.
•  » » 2 years ago, # ^ | ← Rev. 2 →   0 1.0/tan(pi/n)
•  » » 2 years ago, # ^ |   0 C1: 2 times the apothem of the polygon, meaning tan(pi*(2*n - 2)/(4*n)) C2: I have literally no ideea.
•  » » 2 years ago, # ^ | ← Rev. 2 →   0 C1: 1/tan(π/(2n))C2: cos(π/(4n))/sin(π/(2n))
•  » » » 2 years ago, # ^ |   0 can you explain problem C2
•  » » » 2 years ago, # ^ | ← Rev. 2 →   0 is binary search intended solution for C1,C2?
•  » » » 2 years ago, # ^ |   0 Can you explain the solution of C2 ?
•  » » » 2 years ago, # ^ |   0 Hey can u explain one thing tan(angle) = tan(angle*(pi/180)) then in case of tan(pi/(2n)) why it is not equal to tan((pi/180) * (pi/(2n))) ....please help me in this:)
•  » » 2 years ago, # ^ |   +27 Here is how to solve C1 (C2 is a whole other story). It requires you to know a little bit of trigonometry (sin, cos, tan formulas)Take a look at the above image, what we are looking for is the blue line. If we find the length of the line we can double it and that is our answer.How to do that: We can find the angle x by dividing 360/n where n is the number of vertices. Now we need to divide that by two so we can have half the x angle, lets call v = (360/n)/2 = 360/(2*n)We managed to create an imaginary right triangle and we know one angle (v) and the opposite side (with length 1/2 = 0.5), notice that the blue line is the adjacent to the angle v.Tan formula: tan(v) = opposite/adjacent For our case we solve for the adjacent and we have adjacent = opposite/tan(v) = 0.5/tan(v)So i hope that now it is clear that our answer is 2*(0.5/tan(360/(2*n))), just remember to double the n value at the beginning because we look for a 2n-agon.
•  » » » 2 years ago, # ^ |   0 I saw a bunch of submissions of c1 by doing some sort of summation of cosine of angles. what was that all about?
•  » » » » 2 years ago, # ^ | ← Rev. 2 →   0 Some people solved both C1 and C2 with the same code and made the same submission. I guess that C2 requires some addition. I didn't manage to solve it but I think that the solution can be broken down to finding two different sides that sum up to the total square side. (or at least that was my approach)
•  » » » » » 2 years ago, # ^ |   0 So C1 and C2 are not suitable for pupils(I mean students of primary schools). :(Luckily I find out the solution :D
•  » » » 2 years ago, # ^ |   0 why can't we use sin() to calculate directly please explain. My approach was same i just used sin, so that sin(x) = side(0.5)/radius hence radius radius = side(0.5)/sin(x).
•  » » » » 2 years ago, # ^ |   0 Because sin = opposite/hypotenuse in our case we don't need the hypotenuse but the adjacent. You could use both sin and cos to factor out hypotenuse and solve for the adjacent (because tan = sin/cos) but is simpler to use the tan formula instead.
•  » » » » » 2 years ago, # ^ |   0 ohh there i go wrong i was actually taking hypotaneous. thank u very much for correcting me.
•  » » » » » 2 years ago, # ^ | ← Rev. 11 →   0 .
•  » » » » » » 2 years ago, # ^ |   0 By using sine, we will get the circumcircle radius right?
•  » » » » » » » 2 years ago, # ^ | ← Rev. 3 →   0 .
•  » » » » » » » 2 years ago, # ^ |   0 yes, somehow I got messed up with diameter of circumcircle and side of square. haha
•  » » » 2 years ago, # ^ |   0 Thanks for the explanation.
 » 2 years ago, # |   +120 What's the point of problem C?
•  » » 2 years ago, # ^ | ← Rev. 2 →   0 Twice the apothem of the polygon is the side of the square [C1] https://en.wikipedia.org/wiki/Apothem
•  » » 2 years ago, # ^ |   +17 It seems C1 is without rotation, and C2 has a slight rotation, but I didn't manage to find out by how much
•  » » » 2 years ago, # ^ |   +6 Same with you, and for C1 I even dont know how to get the accurate answer, I just tried and tried and finally get the answer which I even dont know why.For C2, I just continued to try, but unfortunately, I didnt get the answer. I find some rotation might be correct but seems it is just my guess not the answer.
•  » » 2 years ago, # ^ |   +33 Mathforcse /cy/qiang
•  » » » 2 years ago, # ^ |   +8 stO Qiuly Orz
 » 2 years ago, # |   0 Why does lazy propogation give TLE/MLE for problem D.80500739
•  » » 2 years ago, # ^ |   0 Memory limit is 28mb.
•  » » » 2 years ago, # ^ |   0 How can this problem be solved using segment tree WTF?
•  » » » » 2 years ago, # ^ |   0 A classic segment tree uses 4*N memory (I've heard this can be tightened, but I use the 4*N version). So you'll keep a leaf for every possible value in the set, representing the count of elements in the set with that value. Then you build the ST saving the sum of children. So, when you are asked to add an element K, you can do that in O(log(N)) adding 1 to every node in the path from leaf to root. If you are asked to remove the Kth element, you make a "binary search" over the segment tree. This is, if you are in node A:*Is the left leaf enough to find at least K elements? That means to check if ST[A*2] >= k. If it is, then you'll recursively find the Kth element in that branch *Is the left leaf not enough? Then you go to the right leaf, recursively, but the call will be query(A*2+1, k-ST[A]) because the left leaf will cover part of the "prefix" you are looking for, so you need to subtract it from K.There's a base case, when A is a leaf, you simply return the value associated to that leaf. Once you've found that value, you also need to update the ST by substracting 1 to every node in the path from leaf to root. So you see every operation is log(N)
•  » » » » 2 years ago, # ^ |   0