### ch_egor's blog

By ch_egor, 3 years ago, translation,

Hi!

This Sunday will take place All-Russian olympiad for students of 5-8 grades, in the name of Keldysh. Good luck to all the participants! Olympiad is conducted under the guidance of the Moscow Olympiad Scientific Committee, in particular GlebsHP, ch_egor, Endagorion, vintage_Vlad_Makeev, Zlobober, meshanya, cdkrot, voidmax, grphil and, of course, Helen Andreeva.

We are happy to announce the Codeforces Round #657 (Vintage Codeforces Round #3) based on the problems of this olympiad! It will be a Div. 2 round, which will take place at Jul/19/2020 12:00 (Moscow time). You might have already participated in rounds based on the school olympiads, prepared by Moscow Olympiad Scientific Committee (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541, 545, 567, 583, 594, 622, 626) as well as vintage rounds (rounds 626 and 628).

The problems of this olympiad were prepared by DebNatkh, grphil, KiKoS, voidmax, I_love_myself, 300iq, isaf27 under the supervision of grphil.

Thanks ch_egor, vintage_Vlad_Makeev and meshanya for their help in organizing the Codeforces version of this contest and MikeMirzayanov for the Codeforces and Polygon.

Also I would like to thank the Tinkoff company and personally Tatyana TKolinkova Kolinkova for great help with organizing the competition.

Good luck!

UPD1: Scoring distribution: 500 — 750 — 1250 — 1500 — 2500 — (1500 + 1500)

UPD2: Editorial

UPD3: Winners!

Div. 2:

Div. 1 + Div. 2:

• +236

| Write comment?
 » 3 years ago, # |   +11 Number of problems?
•  » » 3 years ago, # ^ | ← Rev. 3 →   -78 [Deleted]
•  » » 3 years ago, # ^ | ← Rev. 3 →   -62 [Deleted]
 » 3 years ago, # | ← Rev. 2 →   -86
•  » » 3 years ago, # ^ | ← Rev. 2 →   -69 You can not call it back , until it finish !
 » 3 years ago, # |   -46 I am excited to see problems of Russian olympiad
•  » » 3 years ago, # ^ |   +26 Now after seeing them, u should be depressed.
•  » » » 3 years ago, # ^ |   0 yes I am depressed
 » 3 years ago, # | ← Rev. 2 →   -138 .
 » 3 years ago, # | ← Rev. 4 →   -61 [DELETED]
 » 3 years ago, # | ← Rev. 2 →   -57 .
 » 3 years ago, # |   +177 The last time I saw these many reds was when I witnessed an accident.
 » 3 years ago, # |   +35 What are vintage rounds?
•  » » 3 years ago, # ^ |   -45 I think those rounds in which vintage_Vlad_Makeev is involved.
•  » » » 3 years ago, # ^ |   +22 I don't know what's a vintage round,but it's definitely not a round in which vintage_Vlad_Makeev is involved . (This round for example)
 » 3 years ago, # |   -9 Can I be BLUE....
•  » » 3 years ago, # ^ |   +30 not with the HARDEST div.2 ever.
•  » » » 3 years ago, # ^ |   0 Atleast for me it was the hardest.
 » 3 years ago, # |   +737 No offence to anyone
•  » » 3 years ago, # ^ |   +7 So true!
•  » » 3 years ago, # ^ |   +26 Damn true. Even the school kids will solve till F and we would be struggling with C and D XD
•  » » 3 years ago, # ^ |   +66 Well I take offense SpoilerI wanted to hack Google Headquarters in my first semester.
•  » » » 3 years ago, # ^ |   +3 Some big aim you had in your first year! Most desi Indians only think about hacking Facebook when starting in CS :P
•  » » » » 3 years ago, # ^ |   +1 And some opt cse only for this aim :)
•  » » 3 years ago, # ^ |   +57 Our education system needs improvement, If I would have started coding from my 5th grade then I think I would have been red coder till now, and I beleve its true for all Indians.
•  » » » 3 years ago, # ^ | ← Rev. 2 →   -21 Nah ! If i ask a random 5th grade Indian student to start cp ,he/she would not be even be excited or motivated about it. Exceptions do exist but i am talking with respect to general population . I was more interested in playing football and cricket at that age .
•  » » » » 3 years ago, # ^ |   +23 but what they taught in schools can be changed to what we want to be taught depending upon your interests which will eventually help us in future
•  » » » » 3 years ago, # ^ |   +36 Even I was more interested in playing cricket, but I do wonder if I got introduced to CP I may have latched on to it because I had a good interest in maths and aptitude at that age and also CP has a gaming front to it with all the rankings and points, you just need a given the proper introduction and some good peers to compete with :)
•  » » » » » 3 years ago, # ^ |   +24 True Indian education system sucks
•  » » » 3 years ago, # ^ |   +6 Yeah many of us feel the same, but no probs curently CP is rapidly evolving in India. India will have good number of GM's after a decade or so. And we need to create awareness about CP for a 5th grade student.
•  » » » 3 years ago, # ^ |   +15 I remember learning paint in 5th grade in school lol
•  » » » 3 years ago, # ^ | ← Rev. 2 →   0 If coding from (5th grade -> today) = red coder then coding from (today -> today + 10 years) = red coder too. On top of that at this stage one will need much lesser time maybe 4-5 good years is enough.
•  » » 3 years ago, # ^ |   +5 The same happens in Peru, but with the 5th semester students. From the 1st to 4th semester they just use microsoft excel.
•  » » 3 years ago, # ^ |   +2 I wanted to code when I was a kid but didn't know where to start
•  » » 3 years ago, # ^ | ← Rev. 2 →   +13 Logged in, only to upvote you.
•  » » 3 years ago, # ^ |   -10 Our tradition is to memorize maths to pass exams.
•  » » 3 years ago, # ^ |   +14 Would gladly take this over 70 years of communism.
•  » » 3 years ago, # ^ | ← Rev. 2 →   -6 So hard to accept our education system
•  » » » 3 years ago, # ^ |   +3 you can't blame it on education system ..... NO
•  » » 3 years ago, # ^ |   +31 If this contest was for 5-8 grade students, I feel like I am a new born baby.
•  » » 3 years ago, # ^ |   0 Can feel this bro :')
 » 3 years ago, # | ← Rev. 2 →   -37 Schools are like: Taught in Class: Div2 A Solved for practice: Div2 B Homework: Div2 C Exams: Div2 D,E,F credits: adzo261
•  » » 3 years ago, # ^ |   +12 copied from Here ?
 » 3 years ago, # |   -6 why is that unusual time ?
•  » » 3 years ago, # ^ |   +4 Because problems took from olympiad and for prevent leaking it, round will be in the same time as olympiad
•  » » » 3 years ago, # ^ |   0 tks :))
 » 3 years ago, # |   +55 me in 8th grader : tell my friend to open page 69th of biology book where there is a picture of penis anatomy russians 8th grader : solve div2 problems
 » 3 years ago, # |   -7 Will the round be rated ch_egor? Asking because its not stated in the blog post:)
•  » » 3 years ago, # ^ |   +14 See the last word!!!
 » 3 years ago, # |   -16 great !! we have 300iq now ... I am excited !!
•  » » 3 years ago, # ^ |   -9 Wow! Even einstein had 160. CF must be proud to have you guys :p
•  » » » 3 years ago, # ^ |   -21 I've got 204.
•  » » » » 3 years ago, # ^ |   0 I'm really surprised you don't have 420, that's not that far away.
•  » » » » 3 years ago, # ^ | ← Rev. 2 →   0 "People who boasts about IQ are losers" ~ Stephen Hawking
•  » » » » » 3 years ago, # ^ |   +1 (f + f)iq = 204iq. It was just a joke :)
•  » » » » 3 years ago, # ^ |   +12 I would have upvoted you if you've said 255iq (ffiq)
•  » » » » » 3 years ago, # ^ |   +1 Explain. I'm actually dumb.
•  » » » » » » 3 years ago, # ^ |   0 ff in hex to decimal == 255
•  » » » » » » » 3 years ago, # ^ |   +9 Now I see why I failed to solve even a single problem today.
•  » » » » » 3 years ago, # ^ |   0 same
 » 3 years ago, # |   +1 That's a lot of red handles
•  » » 3 years ago, # ^ | ← Rev. 2 →   +46 Too many...https://imgur.com/a/Awy9IQJ
•  » » » 3 years ago, # ^ |   -6 Nice catch
 » 3 years ago, # |   -16 Why are there so many down-voted comments in this blog?
 » 3 years ago, # |   +1 (Notice the unusual timing)
 » 3 years ago, # |   -31 I think people should think before voting because even the comments which are not at all negative are downvoted heavily.
•  » » 3 years ago, # ^ |   0 I think people downvote it for fun...lol
 » 3 years ago, # |   0 This is 5 AM in America where I live
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 Considering the lockdown, does the time even mean anything anymore?
•  » » » 3 years ago, # ^ |   +33 Yes, there's something called body clock, which when affected can cause various health problems
•  » » » » 3 years ago, # ^ |   +3 Hmmm Point
 » 3 years ago, # |   +24 Score Distribution?
 » 3 years ago, # | ← Rev. 4 →   +7 ....
•  » » 3 years ago, # ^ |   +1 cook off bro!!!
 » 3 years ago, # |   +6 Any reason why start time is 09:00 UTC, but not 09:05
•  » » 3 years ago, # ^ |   +5 Probably because it's going to be held in parallel with All-Russian olympiad. Also to avoid clash with Topcoder and Codechef rounds.
 » 3 years ago, # |   +3 Hope the problem statements are clear and interesting xD
 » 3 years ago, # |   +5 How many problems and Score Distribution?
 » 3 years ago, # |   +111 Unfortunately, the last 6 months we have seen this instead of the exciting confrontation between tourist and amiya :)
•  » » 3 years ago, # ^ |   0 Nice!!!
•  » » 3 years ago, # ^ |   +39 Rating: users participated in recent 6 monthsSince his last contest was on Feb 17, either he'll take part in another contest or disappear from the global rating in a month.
•  » » 3 years ago, # ^ |   +5 At least he's visiting the site which means he is still alive. :)
 » 3 years ago, # | ← Rev. 2 →   +3 Never mind. :)
 » 3 years ago, # | ← Rev. 2 →   +8 What's the Score Distribution? ch_egor
 » 3 years ago, # |   +4 No Score Distribution and No. of Problems yet? ch_egor
 » 3 years ago, # |   +84 where scoring distribution and number of problems will be published?? ch_egor
•  » » 3 years ago, # ^ |   +90 ch_egor ping
•  » » » 3 years ago, # ^ |   +62 ch_egor ping
•  » » » » 3 years ago, # ^ |   +62 ch_egor ping
•  » » » » » 3 years ago, # ^ |   +64 ch_egor ping
•  » » » » » » 3 years ago, # ^ |   +54 ch_egor ping
•  » » » » » » » 3 years ago, # ^ |   +66 ch_egor ping
•  » » » » » » » » 3 years ago, # ^ |   -89 ch_egor ping
•  » » » » » » » » » 3 years ago, # ^ |   +62 ch_egor ping
•  » » » » » » » » » 3 years ago, # ^ |   +148 lmao. That is some ratism right there.
•  » » » » » » » » » 3 years ago, # ^ |   +18 exit(0)
•  » » » » » » » » » 3 years ago, # ^ |   +19 I like to think this was a game of Russian Roulette and this guy just got killed. RIP
•  » » » » » » » » » 3 years ago, # ^ | ← Rev. 2 →   +4 everyone except him who replied had something to do with the roundtester/coordinator/psetter
•  » » 3 years ago, # ^ |   -30 There will be 5 problems
•  » » » 3 years ago, # ^ |   +3 Noo !! It's 6 distinct problems :/ lier !!
 » 3 years ago, # |   +6 Scoring distribution says it's gonna be SpeedForces.
•  » » 3 years ago, # ^ |   +3 You were totally right.
•  » » 3 years ago, # ^ |   +8 This aged well.
 » 3 years ago, # |   +8 I'm sure some people will join 5 minutes late thinking that round will start at 14:35 IST. :v
 » 3 years ago, # |   +16 Is this Div1?
•  » » 3 years ago, # ^ |   +4 Seems so! Not able to TOUCH a question!!
•  » » » 3 years ago, # ^ |   +4 I think we really need the help of pavan putra hanuman to solve the questions in this contest Xd.
 » 3 years ago, # |   +81 There has been a small typo guys.. it is a Div 1 round..
 » 3 years ago, # |   +44 one hand pushups were easier for me than this round's problems!
 » 3 years ago, # |   +50 I've never seen such DIV 2 contest.
•  » » 3 years ago, # ^ |   +11 I guess this is what "vintage" rounds are :-P
 » 3 years ago, # |   +45 Now I get why Russians dominate in competitive programming. :)
 » 3 years ago, # |   +82 This is for 5th-8th grades?? OKK
 » 3 years ago, # |   +17 I wasn't able to enter codeforces for almost 20 minutes. Anyone else facing the same issue?
•  » » 3 years ago, # ^ |   +47 I entered code forces but couldn't think what to do for the past 40 minutes. Anyone facing this same issue??
•  » » 3 years ago, # ^ |   +24 Good that you didnt enter brother! God saved you from a heart attack!
•  » » 3 years ago, # ^ |   0 Yea me too
 » 3 years ago, # |   +10 Should have rather rushed Bombsite B. On a serious note, is this really what 7th Grade Russians study? That is really impressive, no wonder Russians are such good coders.
 » 3 years ago, # |   +21 Great div1 round!!!!!!!!!
 » 3 years ago, # |   +22 2 minutes silence for all those who were too eager for the round to be rated.
•  » » 3 years ago, # ^ |   +3 __now__or__never__ broh feelings...? :D
 » 3 years ago, # |   +31 After walking through first 3 question:How to unregister???
•  » » 3 years ago, # ^ |   +6 Will be waiting for this ninja technique
•  » » 3 years ago, # ^ |   0 Same ..
 » 3 years ago, # |   +39 OK now I'm looking forward to the editorial after the contest.I'm feeling numb :( Is it a Div.2 round or Div.1 Round?
•  » » 3 years ago, # ^ |   +5 Round by Red round for Red . Screaming Red.
•  » » 3 years ago, # ^ |   0 Lul bruh, I have the exact same pattern of submissions, except I'll become specialist by today evening.
 » 3 years ago, # |   +18 This is meant for students of grades 5-8? Wow.
 » 3 years ago, # | ← Rev. 3 →   +1 worst div2 i ever seen !!upd: I said worst cause its seems more div1 than div2 but named div2.
•  » » 3 years ago, # ^ |   +8 *Hardest
•  » » » 3 years ago, # ^ |   +8 so more room to learn :P
 » 3 years ago, # |   +64 I am proud that I have participated in Div 1 round.
 » 3 years ago, # |   +13 I was getting 504 server error during first 20 minutes. I am feeling blessed.
•  » » 3 years ago, # ^ |   +6 Are you the lucky one?
•  » » 3 years ago, # ^ |   +6 I was having the same issue for a very long time. I think this happened with many people and not just a few of us. There were more than 15k people who registered and on the scoreboard there are only 8000 who have attempted a single problem.
•  » » » 3 years ago, # ^ |   +3 I think this could have been because it was very early morning in the US, so lots registered but not many woke up that early.
•  » » 3 years ago, # ^ |   0 You can always use these lightweight websites m1.codeforces.com m2.codeforces.com m3.codeforces.com in such trouble of server in my case these websites work almost everytime in a live contest.
•  » » 3 years ago, # ^ | ← Rev. 2 →   +6 glad to hear it wasn't only me xDI was afraid I was the only one
 » 3 years ago, # |   +16 feels like DIV1 to me
 » 3 years ago, # |   +58 New technique to manage server load.
 » 3 years ago, # |   +175 This is Div 1 :(
 » 3 years ago, # |   +57 Are you trying to kill those poor 5-8 graders ?
•  » » 3 years ago, # ^ |   +1 They might have completed the problemset by now. Russian kids are seriously genious.
 » 3 years ago, # |   +1 No wonder why tourist is so perfect.
 » 3 years ago, # |   +41 is there any way to undo submission?
 » 3 years ago, # |   +38
 » 3 years ago, # |   +3 Ah, it was good that my connection was lost during the first 30 minutes.
 » 3 years ago, # |   +91
 » 3 years ago, # |   +105 When you realize that this was actually a Div. 1 contest
 » 3 years ago, # |   +6 Hell lot difficult contest!
 » 3 years ago, # |   +1 Was this div 2? this was Div 1 ! Even more difficult , Div 0 maybe
•  » » 3 years ago, # ^ |   0 div -2147483648
 » 3 years ago, # | ← Rev. 2 →   +18 I registered for the contest, I planned to participate in it, but I slept and couldn't wakeup on time. I was feeling bad but then i read the problems and number of submissions. Thank god, i didn't wake up on time! xD
 » 3 years ago, # |   +6 You miss 100 percent of the shots you don't take.
 » 3 years ago, # |   0 why there is no extra registration?
•  » » 3 years ago, # ^ |   +55 so that no one else falls into this trap
 » 3 years ago, # |   +3 this is my first ever contest....I havent even solved a single question
•  » » 3 years ago, # ^ |   +51 Don't worry, its my 21st, and even I couldn't solve a single problem.
•  » » 3 years ago, # ^ |   +25
 » 3 years ago, # | ← Rev. 3 →   +4 Can I see how many problems those 5th-8th graders solved? Might be a motivation for me or myth buster for many!!
•  » » 3 years ago, # ^ |   +2 Sure you can! Check this!
•  » » » 3 years ago, # ^ |   0 How long was the real round?
•  » » » » 3 years ago, # ^ |   +1 4 hours, we had problems from B to F.
•  » » 3 years ago, # ^ |   +2
 » 3 years ago, # |   +39 Before reading the comments I thought I don't deserve to be yellow on CF...
 » 3 years ago, # |   +59
 » 3 years ago, # | ← Rev. 3 →   +4 The the last four div2 contests (excluding the Global round):654 — widely disliked655 — good set but queueforces91Edu — good set but major crash657 — Mere mortals can't solve more than 2 (I agree I'm not of high enough calibre to say all of this but damn it a man needs to vent — I've been at 1750 for 10 contests and I couldn't solve a single one — damn pretests 2)
•  » » 3 years ago, # ^ |   +25 Try to concentrate more on developing problem solving skills than on rating.
•  » » 3 years ago, # ^ |   +1 Finally, I found you another expert, that did 0. And you have a much higher rating than me. I am sorry but I feel better now. ;_;
•  » » 3 years ago, # ^ |   0 A hint : abacab*bacaba needs to Output "NO"
•  » » » 3 years ago, # ^ |   0 Woops, wrong person, sorry.
 » 3 years ago, # | ← Rev. 4 →   +60 Me after not being able to solve a single problem
•  » » 3 years ago, # ^ |   0 can u translate it for us who doesn't know the language?
 » 3 years ago, # |   +46 My son was in 8 grade, Now I don't have a son...
•  » » 3 years ago, # ^ |   0 ROFL
 » 3 years ago, # |   +9
 » 3 years ago, # |   +33 So much implementation :(
 » 3 years ago, # |   0 Div 0 round
 » 3 years ago, # |   0 What is wrong with my A:87342260
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 1 11 abac???caba, answer should be no as they want "abacaba" exactly once
•  » » » 3 years ago, # ^ |   0 You are right, Thanks for the test. Does that mean that I just need to add some cases to my code? Or I will code another solution
 » 3 years ago, # |   +10 What is the third testcase for C?
 » 3 years ago, # |   +53 It's a record. First time 20k participant in div — 1 round.
•  » » 3 years ago, # ^ |   +3 Yet only 8000 dared to submit. Salute to those!
•  » » » 3 years ago, # ^ |   +4 *F for those!
•  » » 3 years ago, # ^ |   0 Exactly XD.
 » 3 years ago, # |   +181 New technique to manage server Load
•  » » 3 years ago, # ^ |   +8 Haha! :D
•  » » 3 years ago, # ^ |   0
 » 3 years ago, # |   +5 How to solve C?
•  » » 3 years ago, # ^ |   +11 We will only buy more than one flowers of only one type iterate to choose this and greedily take other flowers who have ai >= chosen bi
•  » » » 3 years ago, # ^ | ← Rev. 2 →   0 I tried to do like this but it hasn't worked(
•  » » » 3 years ago, # ^ |   0 I tried similar approach but couldn't get past test 5. What did you fix to pass that?
•  » » » » 3 years ago, # ^ |   0 I didn't consider if no ai > chosen b
•  » » » » » 3 years ago, # ^ |   0 I did that too at the end, still failed :( Guess something is wrong with my implementation. Thanks.
•  » » » » » 3 years ago, # ^ |   +5 Oh I found my mistake, I didn't handle this case: Number of Ai >= b is already >= n, in that case, I shouldn't take this b.
•  » » » 3 years ago, # ^ |   0 my idea was similar but I implemented it wrongly I guess. Thanks for replying.
•  » » » 3 years ago, # ^ |   0 I did the same and got WA2 T_T
 » 3 years ago, # | ← Rev. 2 →   +8 Probably it was the hardest was the A ever
 » 3 years ago, # |   +15 I don't see why is it rated for me when I'm clearly not a div1 participant
 » 3 years ago, # |   +1 any hint for problem C !
•  » » 3 years ago, # ^ |   +2 you knew that you should take a[i] at least once to take b[i]. so, first sort all array A, then if we take a[i] once, then we have two options in the next step. take a[i + 1] or (b[i] for all remaining flowers), so think where you will know that you will take b[i] for all remaining flowers. i think this enough as hint. if u wanna more hint or there is anything ambiguous , tell me.
 » 3 years ago, # |   0 What's tc18 for F1?
 » 3 years ago, # |   0 It is kind of funny I visit the CF blogs comment section to see memes.
 » 3 years ago, # |   +1 this contest is for grade 5 to 8,OMG i can only imagine level of Russian kids
 » 3 years ago, # |   +56
•  » » 3 years ago, # ^ |   +65
•  » » » 3 years ago, # ^ |   +11 Are you still a kid or it's just the old dp?
•  » » » » 3 years ago, # ^ |   0 It wouldn't be a surprise if he actually turns out to be an 8th graderno offence :P
•  » » » » » 3 years ago, # ^ | ← Rev. 2 →   +4 Winning ICPC world finals in 6th and 7th grade :orz:
 » 3 years ago, # |   0 Problem A is not as easy as I though, it actually requires more implementation than usual :)
 » 3 years ago, # |   0 How to solve C? I tried a greedy strategy but it is not always optimal, and I believe fixing it would require m^2.
•  » » 3 years ago, # ^ |   0 Why greedy is not always optimal?
•  » » 3 years ago, # ^ |   -6 I think it is something related to convex hull optimization technique.
•  » » » 3 years ago, # ^ |   0 I don't think so! I believe, greedy will work! Even though, I couldn't reach up to a correct solution.
•  » » 3 years ago, # ^ | ← Rev. 2 →   +1 Notice that you will only take b_i of one type in the entire process (if you could improve the answer by taking another b_k, you would just take all b_k as it would be better), and that it is optimal to take all a_j >= to this b_i before taking it and that you must take a_i before you can take b_i. Now you can just iterate over b_i in descending order and do something like two pointer to keep track of the sum of a_j >= b_i taken while maintaining a used array to see if you've taken a_i already when taking b_i, so answer will be max of (asum till now + (n — a_taken) * b[i]), minus b[i] plus a[i] if we haven't used it yet.
•  » » » 3 years ago, # ^ | ← Rev. 2 →   0 I tried same thing. But, might have missed out something in the implementation! :(
•  » » » » 3 years ago, # ^ |   0 Did you clear the used array? I got 2 WAs and wasted 10-15 mins thanks to that
•  » » » » » 3 years ago, # ^ |   0 Actually, I used 2 PQ's to implement this. Maybe, I missed something in the casework.
•  » » » 3 years ago, # ^ |   0 Ahh I see. I tried to implement it backwards (iterate over all a_i in descending order and find the best candidate for b, which I thought was O(1) since you can keep track of the max b already taken and not already taken, but the max is not always optimal. Nice solution!
 » 3 years ago, # |   +5 It seems Div1 round for Div2 participants. Too Hard! ToT
 » 3 years ago, # |   0 Counter case for taking times modulo m / 2 (and ignoring hours), sorting and finding largest range with distance of max m / 2 — k using two pointer in D?
•  » » 3 years ago, # ^ | ← Rev. 2 →   +3 I kind of did the same thing. My solution was failing on this- 4 24 4 2 16 0 17 1 18 2 19 3Try this
 » 3 years ago, # |   +23 "Wrong answer on pretest 2"5 words which summarize the contest
 » 3 years ago, # |   +35
 » 3 years ago, # |   +22 Seems like old codeforces rounds are back. Kudos to the author , Nice educational problemset. I hope more of such rounds which teaches how to solve real algorithmic problems in future, A B C were absolutely fabulous and not as per the score given to them , B is much more worthy than 1000 also. Again Thank You for such a brilliant round.<3
•  » » 3 years ago, # ^ |   0 Yes true many people will complain about how bad the round was just because it was hard but the truth is it was really educational as even the implementation was hard and required debugging skills and the problems logic was also good.
•  » » » 3 years ago, # ^ |   0 Specialists are dumb
•  » » » » 3 years ago, # ^ |   +7 Please have a look at my graph before making assumption :P
•  » » » 3 years ago, # ^ |   0 yeaheverybody is crying but it was quite a challenging round and a nice change
 » 3 years ago, # |   +1 Should I register for next DIV2 round or not?
•  » » 3 years ago, # ^ |   0 Never fear for ratings always assume that they are a sideffect of Leaninig. If losing rating hurts you then also its normal try not looking at standings during the contest and also not at all look at your colour, just believe that giving contest and one like this is making you a learn something new, everyday. and also training you on what you already have learnt. Especially do all those contests given in a list combined in the announcement above. These are some of nowadays rare contest problemsets and amazing. Once again do register and solve problems for fun.
 » 3 years ago, # |   +6 My First Div 1 contest done !! -_-
 » 3 years ago, # |   0 Can someone give a hint for D? Is it a ternary search?
 » 3 years ago, # | ← Rev. 2 →   0 can anyone tell me what is wrong in this solution?? https://ideone.com/rajqqD. This solution is for Acacius and String.
•  » » 3 years ago, # ^ |   0 Buddy submissions won't be visible for 1st hour after the contest(check the announcement) better paste your formatted code here
 » 3 years ago, # |   -11 All these comments and the round is still running? seriously guys!!!
•  » » 3 years ago, # ^ |   0 what?
•  » » 3 years ago, # ^ |   +1 I think people didn't have anything else to do.
•  » » » 3 years ago, # ^ |   0 OK I understand the problems were harder than usual ( and much more interesting :D ) but admins should shout down comments during the contest, what if someone talks about his solution for one of the problems!!!
 » 3 years ago, # |   0 How to solve B?
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 NvmDidn't understand the statement completely
•  » » » 3 years ago, # ^ |   0 You can't get 2 if l > 2
•  » » » 3 years ago, # ^ |   0 But what if l > 2, than a cannot be 2, because a >= l
•  » » » 3 years ago, # ^ |   0 but l is not always 2 so, we can not fix a = 2 always
•  » » » » 3 years ago, # ^ | ← Rev. 2 →   0 My bad I didn't read the problem statement carefully
•  » » 3 years ago, # ^ |   0 Fix a and then try to find b, c.
•  » » » 3 years ago, # ^ |   0 did same still WA. My code for (ll a = l; a <= r; a++) { ll rem = m % a; if (rem == m) rem -= a; if (rem >= l - r and rem <= r - l) { cout << a << " " ; if (rem > 0) cout << rem + l << " " << l << endl; else cout << l << " " << l - rem << endl; goto skip; } } 
•  » » » » 3 years ago, # ^ |   0 Actually you should check for both $rem = m$ % $a$ and $rem = (m + a - 1)$ % $a$
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 You have $n*a + b - c = m => n*a = m + x$ where $x = c-b$ and $m+x \in [-maxr+m,m+maxr]$ where $maxr = r-l$ Iterate over a and do a binary search over $n$ and check if $n*a \in [-maxr+m,m+maxr]$So if you have $n$ and $a$ you can simply fix $b = l$ and calculate $c$.
•  » » » 3 years ago, # ^ |   0 No need for binary search, just find closest values to m you can get by taking positive amounts of a using division.
 » 3 years ago, # |   +2 Thanks for the great contest.
 » 3 years ago, # |   0 Too difficult for me...fighting!!!!
 » 3 years ago, # | ← Rev. 2 →   0 For problem D, I think the hour value of trains wasn't necessary.Was it supposed to be solved by iterating on all "minute" values of trains as a candidate of $t$ and then finding how many minute values intersect the range $[t-k+1, t-1]$?Ofcourse, this will have few cases to consider like $k=1$ or $t  » 3 years ago, # | 0 is it just me?? the codeforces were saying "can't connect right now" by the time contest was starting and after 5 or so minutes later it started. I submitted my C problem solution before 2 minutes but it keeps loading and loading after the contest I checked whether it submitted or not. But it wasn't submitted?  » 3 years ago, # | +1 People before contest were asking — how many problems? Meanwhile ch_egor to himself : Actually there are two problems.  » 3 years ago, # | 0 How to solve C ? is there a greedy approach to it? •  » » 3 years ago, # ^ | 0 optimal flowers choice is to take some flowers only once, and then take one flower and put it to the rest of the slots in bouquet.you have to iterate through that flower which is gonna be put to the rest of the slots and update the answer.  » 3 years ago, # | +28  » 3 years ago, # | +1 Can anyone from Russia covert 5-8 grades to the equivalent level of American or Indian Education system, or at least tell me students of what age group study in Grade 5-8 in Russia? •  » » 3 years ago, # ^ | 0 12-15 years old •  » » » 3 years ago, # ^ | +3 •  » » 3 years ago, # ^ | 0 13-15 y.o.  » 3 years ago, # | +3 Problem B seems easier than Problem A. •  » » 3 years ago, # ^ | 0 it just seems so DDD:  » 3 years ago, # | +58  » 3 years ago, # | +48  » 3 years ago, # | +24 I misread the contest as DIV-2 and registered it. I didn't knew it was DIV-1  » 3 years ago, # | -6 why my B solution is wrong? :(#include #define pb push_back #define getarray(a,n) for(int i=0;i>a[i] #define ll long long #define fast ios_base::sync_with_stdio(false);cin.tie(NULL); #define vi vector #define w(t) int t;cin>>t;while(t--) using namespace std; int main() { fast w(t) { ll l,r,m; ll ans=9999999999999,t=0; cin>>l>>r>>m; bool flag=1; for(int i=l;i<=r;i++) { ll p=m%i; if(p==0) { if(i==l) { cout< •  » » 3 years ago, # ^ | ← Rev. 2 → 0 There are some cases that n*a have to be above mIn this case for example7 8 13 the answer will be 7 7 8 , where n = 2 and 2 * 7 > 13and the m%i method won't work for these cases.  » 3 years ago, # | +1 try this test case if you are getting WA on pretest 2, problem A. 1 12 abacab?cabac  •  » » 3 years ago, # ^ | 0 My code says "NO", and I was still getting WA on pretest 2 •  » » » 3 years ago, # ^ | ← Rev. 2 → +1 Try this test case for problem A111???????caba •  » » » » 3 years ago, # ^ | ← Rev. 2 → 0 Yes ddddabacabaIs the output. I did consider the fact that changing from start and end can have different effects, So I checked in both. •  » » 3 years ago, # ^ | 0 Thanks for the test, but what is the true solution?  » 3 years ago, # | +7 super difficult problem sets, but it was very interesting!  » 3 years ago, # | +5 implementation-heavy round...  » 3 years ago, # | 0 How is the answer for the 2nd test case in problem C is 16.Shouldn't it be (5+4+5+4+5)=23 •  » » 3 years ago, # ^ | 0 you can choose 5,4,3 only once according to the question •  » » » 3 years ago, # ^ | 0 Where it was written in the problem that we can choose those values exactly once.I thought that whenever we switch from one flower to other flower then we can use the ai and whenever we use the same flower consecutively then only bi comes into account or I understood the problem wrong? •  » » » » 3 years ago, # ^ | 0 try reading these lines from ques again_ He knows that after receiving the first flower of the i-th type happiness of his wife increases by ai and after receiving each consecutive flower of this type her happiness increases by bi. That is, if among the chosen flowers there are xi>0 flowers of type i, his wife gets ai+(xi−1)⋅bi additional happiness (and if there are no flowers of type i, she gets nothing for this particular type)._ •  » » » » » 3 years ago, # ^ | 0 Ok I got it. I was confused by the consecutive part. Thought the value bi is added only when we take same number of flowers consecutively,that lead to the confusion of ai part.  » 3 years ago, # | 0 [Deleted]  » 3 years ago, # | +9 Where i can get Russian students Textbook for Computer , Maths (class 5 — 8th) in English . How they prepare , any resource which they use ?? Please tell , (currently i am in university , but was unable to solve this contest).  » 3 years ago, # | +41 There are lots of people (me included), who find the problems to be too hard for Div2 round. Please don't be so dissatisfied about it, because: Rating. The problems were harder for everybody. Everybody solved less problems than they expected to, and the rating changes will be generally the same. It's ok to solve 0 problems in this round. It's not because you're bad, it's because the round is hard! Remember to check editorials and solve some of the problems after the round ends!  » 3 years ago, # | +19 First time absolutely sure before System Tests that my solutions wouldn't fail because they didn't get accepted in the first place.  » 3 years ago, # | ← Rev. 2 → +30 Spoiler  » 3 years ago, # | 0 I feel injured  » 3 years ago, # | 0 Anyone solved C using Priority_Queue?? what approach you used to solve Problem C •  » » 3 years ago, # ^ | ← Rev. 2 → 0 [Deleted]  » 3 years ago, # | 0 can use sweep line on Problem D. But I have no time to implement it.  » 3 years ago, # | +8 For E, is there a more efficient construction than:  o / \ o o / \ o o / \ o o / \ o etc. I believe this should work for$2k + 3 \leq n\$, but I'm not super sure...
•  » » 3 years ago, # ^ |   +13 I solved E with this technique, but there is a special case: if n =9 and k=2, then the answer is NO.
 » 3 years ago, # |   +32
•  » » 3 years ago, # ^ |   0 In Problem B. :(
•  » » » 3 years ago, # ^ |   0 In all problems :((((((
 » 3 years ago, # |   -10 One word to describe today's contest for me — CHAOS.
 » 3 years ago, # |   -31 I request Codeforces to make it unrated for those , who were not able to solve even single problem . I never thought a contest for 5-8th grade student will be so much tough .
•  » » 3 years ago, # ^ |   +22 Very interesting idea. Also good idea is to make it unrated for people who are losing rating.
•  » » 3 years ago, # ^ |   0 You don't know how stressfull it was, and now predictor says imma get 93 rating increase. so i would never want it go unrated.
 » 3 years ago, # | ← Rev. 2 →   0 How to solve B ?? looked easy but was not.My approach : I iterated from l to r and took the modulas and checked for m % i != 0 is l + (i — m % i) <= r.for m % i == 0 just print i but this approach is wrong can anyone explain why ??
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 CHoose a particular value of i between l to r as a and binary search from 1 to m for n. and choose any feasible numbers n,b,c which satisfy the equation. n*a+b-c=m
 » 3 years ago, # |   +2 I couldn't access the codeforces site the moment this contest started and I can access again after the contest has ended. I had to use vpn to give the contest. Did something like this happen with anyone? Also, any solution?
•  » » 3 years ago, # ^ |   0 Same. Just use m1.codeforces
 » 3 years ago, # |   0 They should at least give a warning for such a contest.
•  » » 3 years ago, # ^ |   0 But they thought we were as good as the Russians kids DD:
 » 3 years ago, # |   +19 A historic moment! Everyone including the newbies were allowed to get a feel of DIV-1 contest :P
 » 3 years ago, # |   +5 In problem D, what was the point of printing the indices of cancelled freight trains too? We are already printing minimum cancellations and the optimal starting time.
 » 3 years ago, # |   +1 Test case for A: 1. abacab?bacaba -> NO 2. abac?b?bacaba -> YES -> abaczbabacaba
 » 3 years ago, # |   0 i solved prob A just 20 minutes and prob B 3 minutes before contest ended, there was some corner cases that i did't come up with during that time, in my opinion i really like this round, great problemsets with non-trivial test cases, reminds me of how airheaded i am
 » 3 years ago, # |   0 What is the counter for the following approach in D. Find the time intervals for each train where it will be skipped because of passenger trams. Then do something similar to prefix sums and find the time where minimum trains will be skipped.
•  » » 3 years ago, # ^ |   0 The intervals follows a certain sequence for each time so they can be calculated.
 » 3 years ago, # |   +5 Not to offend anyone, but keep in mind that the mere fact that tasks for 5-8 grade students are hard doesn't imply they're really good at CP. Measure the skills of participants by the number of problems solved, not by the hardness of the problems prepared by organizers.
 » 3 years ago, # |   +39 me:
•  » » 3 years ago, # ^ |   0 if a participant make no submission in a round, round will be unrated for him/his ?
•  » » » 3 years ago, # ^ |   0 Yes, he/she will not be in the standing if he/she don't make submissions
•  » » » » 3 years ago, # ^ |