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### Alexdat2000's blog

By Alexdat2000, 6 months ago, translation,

Greetings to all humans and robots on this site!

sevlll777, crazyilian, Mangooste, imachug and me (Alexdat2000) invite everyone to participate in the Codeforces Round #770 (Div. 2), which will take place this Feb/06/2022 17:35 (Moscow time). This round will be rated for all participants with a rating of strictly less than 2100. You will have 2 hours and 30 minutes to solve 6 problems. There will be an interactive problem in the round, so we recommend all new participants to read Interactive Problems Guide.

Scoring distribution: 500 — 1250 — 1500 — 2000 — 2500 — 3000.

Codeforces Round #770 (Div. 2) is ready to resist the rise of machines
Do you think you are stronger than a robot or not?

We wish all participants high rating! Show that people are still worthy!

UPD: Editorial

• +957

 » 6 months ago, # | ← Rev. 2 →   +296 As a tester I don't lose to AI in this round xD
 » 6 months ago, # |   +359 it would be funny if AI won't be able to solve a single problem
•  » » 6 months ago, # ^ |   -52 Github Copilot should also participate.
 » 6 months ago, # |   +33 Super excited (and kinda scared) to see an AI competing in a CF contest! Congratulations to the responsibles for such an amazing advance in the field of Artificial Intelligence (and my future nightmares)
 » 6 months ago, # | ← Rev. 3 →   +3 ‎Sorry AI, not today!
 » 6 months ago, # |   +244 Well this meme just became reality XD
•  » » 6 months ago, # ^ | ← Rev. 2 →   +174 Another Meme :)
•  » » » 6 months ago, # ^ | ← Rev. 2 →   -26 They still don't think btw not saying AI sucks it's phenomenal but it's different process
•  » » » » 6 months ago, # ^ |   +11 Why don't you define what "thinking" is for us
•  » » » » » 6 months ago, # ^ |   -21 You're just one of the over hyped blind people . Did Beethoven train himself on anything similar to the pieces he wrote ? What you could do to train neural networks to write music you just put so many samples so it could extract the patterns and then it tries to do something with it . We don't count on the patterns we can deduct things and ideas that can't be transformed into digital data and as I said The AI is amazing but it's different I'm not trying to say that it's not interesting it's the future
•  » » » » » » 6 months ago, # ^ |   +8 It solved backspace... I don't know what "thinking" means but that's not trivial at all and I was very surprised it managed to do so. Definitely doing more than just implementing a problem statement.
•  » » » » » » » 6 months ago, # ^ |   0 if we don't know what thinking is then how could we say the AI thinks the computer doesn't think it only calculates .. but the point is this process is different from ours . For example how could you train the neural network to write a joke with that kind of process that will never make it write an actual new funny joke and that's the difference digital data can't save all of our ideas in a way the computer can understand and use this information to create and it will only create things based on samples it was trained but we can close our eyes and imagine something that never existed and make it come true (like a war for example let's kill each other isn't that beautiful) i know the joke isn't in the right place XD
•  » » » » » » » » 6 months ago, # ^ |   +13 By this metric a machine will never be able to think even after its ability surpasses human ability
•  » » » » » » » » » 6 months ago, # ^ |   0 when it comes to calculations the machine will always surpass the human but the problem is the way it calculates is different when a human wants to calculate 1+0=1 that's similar how the computer calculate but when we need to know is that a dog or a cat we simply know it in instance but the AI should get every pixel in the image and compare it with the previous data to decide but should we call that thinking ? for someone that doesn't know what AI is will say this is thinking but it's actually calculations and this is something we have we do calculate but that's not the only thing we have when someone just simply deduct an idea that never existed before we could call that intelligence I guess and I don't mean an idea that never existed in the world but he was never trained to anything that helped him to build that idea and for me I prepare samples by myself to train the neural network and if i fail to prepare the samples in a certain way the AI gets confused and can't decide anything
•  » » » » » » » » » 6 months ago, # ^ |   +9 Actually, I think that some processes in our brains are similar to what NNs do. For example, image recognition part could be quite similar. On the other hand, when it comes to understanding things and abstract reasoning then the processes are really different.
•  » » » » » » 6 months ago, # ^ |   +5 All of the creative things about human are result of billions of years evolution. It took many trial and error to reach that phase. Humans are still far from perfect being. AI already doing some impressive task. I don't see why AI cant acquire characteristics that humans or others animals have and be better at it.
•  » » » » » » » 6 months ago, # ^ |   0 before the human was able to invent some machine that walks 50 miles per hour and the speed kept increasing but that doesn't mean we will invent something that can travel at the speed of light someday there are limitations always . Anyone who worked with neural networks knows the limitations and the AI isn't evolving by itself that's the human job to develop it
•  » » » 6 months ago, # ^ |   +25 One more meme :)...
•  » » 6 months ago, # ^ |   0 I am a newbie and I am proud to do better than AI :D
 » 6 months ago, # |   +170 Let's write complex explanation in the problem statement so the AI doesn't understand shit muahaha
•  » » 6 months ago, # ^ |   0 Then maybe I can't understand as well. T^T
 » 6 months ago, # |   +14 We shall leave competitive programming to our robot overlords.Jokes aside, this is pretty interesting! I'm looking forward to seeing the results
 » 6 months ago, # |   +180 As a tester, I highly recommend to participate (yep, the quality of all problems is insane)! SpoilerI'm sure that AI will solve nothing (unfortunately). I'm ready to apologize if I'm wrong.
 » 6 months ago, # |   +4 AI vs coders: let's conquer Ai guyz(What if I am afraid as hell to lose to an AI).
 » 6 months ago, # |   +92 We are happy to be the authors of the first round that AlphaCode will participate in. Now we need story in questions.
 » 6 months ago, # | ← Rev. 2 →   +8 God bless me . At least In this, I want to defeat AI.
 » 6 months ago, # |   +55 Imagine AlphaCode FST'd
•  » » 6 months ago, # ^ |   +102 Will it downvote the round announcement blog then lol?
 » 6 months ago, # |   +175 Will AI steal all of the tester jobs???
•  » » 6 months ago, # ^ |   -11 Not all!
•  » » 6 months ago, # ^ |   +37 Probably not in the April Fools Day Contest)
•  » » 5 months ago, # ^ |   0 Can't text u back on codeforces due to quota limit. Would u mind giving your email id?
 » 6 months ago, # | ← Rev. 2 →   +67 meme
 » 6 months ago, # |   +106 Just imagining out of curiosity...The face of AI after WA on Pretest 2 XD
 » 6 months ago, # |   +246 will be so funny if all three of them get disqualified for same solution
•  » » 6 months ago, # ^ |   +17 These are submission of the three AIs for the problem 1623A - Robot CleanerAnd these are totally different from one another. But still you have a valid point
•  » » » 6 months ago, # ^ |   +18 I like that they even use debug print statements and then comment them out lol
•  » » 6 months ago, # ^ |   +5 If SelectorUnlimited solves only A, WaggleCollide solves only B, and AngularNumeric solves C and D... Can we consider all of them to be the same user "AI", which solved A, B, C, and D?
 » 6 months ago, # |   +100 This is the moment our future is going to be decided.We either dominate those ridiculous bots or they're going dominate us in the future. I need one hundred percent effort from each one of you participating. We need to freaking crush them once and for all.Everybody focus this round — this time it's not about rating, it's about something bigger.Good luck humans
•  » » 6 months ago, # ^ |   +28 Shinzo wo Sasageyo!
•  » » » 6 months ago, # ^ |   -7 Shinzou Sasageyo!!
•  » » 6 months ago, # ^ |   0 the future is inevitable. My only choice is to go find a rich lady who is into Asian boys
•  » » » 6 months ago, # ^ |   0 nice choice :DD
•  » » 6 months ago, # ^ |   0 Spoiler
•  » » 6 months ago, # ^ |   +11 Tatakae!!
 » 6 months ago, # |   +8 How to say all the best to AI
•  » » 6 months ago, # ^ |   +39 Train them with authors' solutions :)
•  » » » 6 months ago, # ^ |   +70 Why not train me with author solutions. I will win this war for humans :p
•  » » » » 6 months ago, # ^ |   +31 Why not train authors with author solutions
•  » » » » » 6 months ago, # ^ |   +19 That doesn't make sense... Does it?
•  » » » » » » 6 months ago, # ^ |   0 Everything makes sense maybe not perfect.
 » 6 months ago, # |   0 Best Wishes, AlphaCoders!
•  » » 6 months ago, # ^ | ← Rev. 2 →   -36 :(
 » 6 months ago, # |   +17 As a tester, I hope I'm stronger than AI. Have a good first round of human vs AI!
•  » » 6 months ago, # ^ |   0 what is his id
 » 6 months ago, # |   +5 Well,Alphacode!That sounds so interesting!
 » 6 months ago, # |   +42 It would be scary if those AI can use strong computing ability to stress test all coders in the same room as them. If the round is edu or div.3 they may be the best "hackers" XD
•  » » 6 months ago, # ^ |   +8 Didn't see that coming
 » 6 months ago, # | ← Rev. 2 →   -13 I don't even believe AI can solve problem A in div2, wait and see
•  » » 6 months ago, # ^ |   0 It has already solved even E: https://codeforces.com/submissions/AngularNumeric
•  » » » 6 months ago, # ^ |   0 The company that developed it estimated that it was 1238 points, so it was surprised that it could solve E
•  » » » » 6 months ago, # ^ |   0 ...users who have participated in at least 1 contest in the last 6 months. AlphaCode’s estimated rating is in the top 28% among these users.Aha... We will see, how it can perform in a real contest situation.
•  » » » » » 6 months ago, # ^ |   +14 It's so unfair, machines don't have to handle ongoing contest anxiety.
•  » » » » » » 6 months ago, # ^ |   0 And they are not afraid of losing to AI.
 » 6 months ago, # | ← Rev. 2 →   +8 guys to whom you bet your money on? ME or Alpha Code (you can take a look at my profile before betting)
•  » » 6 months ago, # ^ |   +11 definitely you man go crush AI
 » 6 months ago, # |   +45 Well, I am all set to get my revenge back for being beaten by AlphaGo xD
•  » » 6 months ago, # ^ |   +5 Good luck! :)
 » 6 months ago, # |   +3 CP contests were never more interesting.
 » 6 months ago, # |   0 It is time to give the way for John Connor.
 » 6 months ago, # |   0 Time to introduce flavor text.
 » 6 months ago, # |   +31 Pretty scared AI will beat everyone. Spoiler
 » 6 months ago, # |   +118 If Anton is coordinator, no way that AI solves more than one problem...
 » 6 months ago, # | ← Rev. 2 →   -21 I'm willing to compete against AI this Sunday!! I stopped playing chess because of AlphaZero, is someone thinking of retiring if AlphaCode performs better than humans?Yes, I wanna retire and live far away in the mountains NO, I WILL STILL FIGHTING
•  » » 6 months ago, # ^ |   +56 I stopped playing chess because of AlphaZero Stockfish was not strong enough? :)
 » 6 months ago, # |   +16 It would be great if tourist participates in this round. We would get to see tourist vs alphacode. I don't know why but I feel like tourist will win.
•  » » 6 months ago, # ^ |   0 AlphaCode current rating is estimated to be 1238 points. I am sure tourist will win against a pupil.
•  » » » 6 months ago, # ^ |   +4 Oh, really? I actually didn't know this. Thanks for sharing.
 » 6 months ago, # |   0 Wow! 1250 score distributed for the second problem? Is that more score than usual?
•  » » 6 months ago, # ^ |   -10 Yes, the score is deliberately higher than usual.
•  » » » 6 months ago, # ^ |   +25 to make Ai go brrrr.
 » 6 months ago, # |   0 Don't let the robots defeat us!
 » 6 months ago, # |   +4 Soon I could boast that I had dueled with AI on behalf of mankind. XD
 » 6 months ago, # |   +1 May be in the future, AlphaCode will host rounds(and create them)
 » 6 months ago, # |   0 So will it happen that AplhaCode will have his own account on codeforces ? and also he will be regular with the competitions?
 » 6 months ago, # |   0 Come on AI lets have a fair game, i hope you a win today but not in future..
•  » » 6 months ago, # ^ |   +1 Reverse.
 » 6 months ago, # | ← Rev. 3 →   +12 Hope that tourist can fight back for mankind. Best wishes.
•  » » 6 months ago, # ^ |   +1 AlphaCode's rating is predicted to be in the range Pupil-Specialist. So tourist need not fight, even we can :rofl
 » 6 months ago, # |   0 all three AI will write same code??
 » 6 months ago, # |   -9 I hope everyone will raise their ratings after giving this contest
•  » » 6 months ago, # ^ |   +21 The rating is calculated in such a way that the mean rating change is zero. Therefore it can't be all positive. Just saying.
•  » » » 6 months ago, # ^ |   +8 toxic
 » 6 months ago, # |   +40 As a tester, I'm happy to return red colour :)
 » 6 months ago, # |   +3 Humanforces vs AIforces
 » 6 months ago, # | ← Rev. 3 →   +16 Maybe you have forgotten to notice AlphaCoder's accounts, like me before.SelectorUnlimitedWaggleCollideAngularNumeric
 » 6 months ago, # |   0 If we create a problem with a well-written and AI-friendly description where the task is to create an AI to solve Codeforces problem, will the AI understand it and create an AI like itself?
 » 6 months ago, # |   -14 There are several ways DeepMind can cheat: — some of the writers/testers are related to DeepMind, so * the problem statement is made easy for the AI to understand, or * even worse, the problems may be leaked — humans could rephrase the problem statements so the AI can understand — or simply, humans can submit a solution instead
•  » » 6 months ago, # ^ | ← Rev. 2 →   0 No authors are connected to DeepMind whatsoever, and I'm 95% sure the same holds for testers. And no, the statements weren't trained on the AI, so to speak. As for the last option, well, the goal is not to deliver a message or prove a point but to perform an in-field run, so I doubt that would happen either.
•  » » » 6 months ago, # ^ |   0 Who knows about the human submitting the solution maybe if the results were so embarrassing something like that could happen
•  » » » » 6 months ago, # ^ | ← Rev. 2 →   -9 I can't see any possibly embarrassing circumstance in which such measures would be meaningful. No one seriously expects AlphaCode to solve more than one problem, if that. Saying "we tried" or "it worked after we rewrote the statement formally" is fine.
•  » » » » » 6 months ago, # ^ |   0 I guess you're right it's completely pointless if it didn't work they will have to lie every time . never mind that was stupid thought
 » 6 months ago, # | ← Rev. 2 →   0 I don't care about the bots as I think I will perform better than them more often than not.But I think they should be in seperate standings because many grays may struggle fighting with them
 » 6 months ago, # |   0 This contest will be harder than previous contest
 » 6 months ago, # |   +28 Please Provide the user id with which AlphaCode will participate. I wanna add him as friend.
•  » » 6 months ago, # ^ |   +18
 » 6 months ago, # |   +15 Will the AI spam wrong solutions until it gets a correct solution? lol it will be fun to see.
 » 6 months ago, # |   +3 Imagine if AI rage quit on problem A!
 » 6 months ago, # |   +6 As an AI I feel sad.
•  » » 6 months ago, # ^ |   +44 "As an AI" "I feel" Choose one xD
 » 6 months ago, # |   -13 Can AC (AlphaCode) can get AC in an Interactive Problem? Because Humans can.
 » 6 months ago, # |   -13 AlphaCode gonna destroy me..
 » 6 months ago, # |   +19 AlphaCode (after being underestimated by the community)-> AlphaQ
 » 6 months ago, # |   +3 Would the AI solving multiple problems at a time, or just single one? Their submission time are so close. submissions
 » 6 months ago, # |   +45 It seems very unlikely that these robots are able to solve problems above 1500 accoding to their submissions. :)
 » 6 months ago, # |   +7 People talking AI can solve this that, SpoilerMeanwhile AI solution getting skipped :xD
 » 6 months ago, # |   0 Hope I will reach to the pupil today. Waiting for very long.
•  » » 6 months ago, # ^ |   +16 Good luck!
 » 6 months ago, # |   0 This battle will be legendary!
 » 6 months ago, # |   +3 Why are there three AI bots? Why not combine them to create one super bot (which uses all three solutions one by one)?
•  » » 6 months ago, # ^ |   0 Well either they are the same model in the end or they want to compare performance of different methods. Don't forget that the momentary goal is not to win; the goal is to find out how to win.
•  » » 6 months ago, # ^ |   +30 Oh, gr8. When 3 AI bots compete from as a single account, they're a super bot.but when my 3 friends do the same, they are called a ... cheater? smh.
•  » » 6 months ago, # ^ |   +14 girl on codeforces rare ,indian rarer , expert rarer^2
•  » » » 6 months ago, # ^ |   -8 sexist on codeforces common, indian commoner, below expert commoner^2
 » 6 months ago, # |   +131 The paragraph mentioning AlphaCode participation is now gone?
•  » » 6 months ago, # ^ |   +440 Yeah guys We are very sorry to inform you thatwe fucked up due to some technical reasons that we are working hard onwe misinterpreted a meme as a secondary source some miscommunication has happened within the team andthere was literally zero chance AlphaCode would participate in a live contest it is unlikely that an in-field test will be performed at such an early stage of the project.
•  » » » 6 months ago, # ^ |   +213 AlphaCode:
•  » » » 6 months ago, # ^ |   +78 So sad to read it. I was eagerly waiting to defeat bot in this round. ):
•  » » » » 6 months ago, # ^ |   0 These are some of the last months in which we can say we defeated a robot.
•  » » » » 6 months ago, # ^ |   0 Better i didn't participated this round
•  » » » 6 months ago, # ^ | ← Rev. 3 →   0 it is unlikely that an in-field test will be performed at such an early stage of the project.AI will wait for a Div 3 contest :) P.S.How do you strikethrough a line? :/
•  » » » » 6 months ago, # ^ |   +5 text
•  » » » » » 6 months ago, # ^ |   +5 If this works, why is it not strikethroughed for you?
•  » » » » » » 6 months ago, # ^ |   +5 Because when you type text you really do get text, and if you want to type text you have to type <s>text</s> (and to type that, you have to HTML-escape it once again, and so on)
•  » » » » » » » 6 months ago, # ^ |   0 Thanks, appreciate it <3.
 » 6 months ago, # |   +15 Hey cheaters! Now is your time! You can copy the AI's code and make it skipped! Ahahahahahaha! For the human begin!
 » 6 months ago, # |   0 Interesting question: Will AI skip some problem in order to solve other problems that are maybe will be easier or AI will solve problems one by one. (For example skip C to solve D and etc).
•  » » 6 months ago, # ^ |   +89 It looks like AI skips the whole contest.
 » 6 months ago, # |   0 Good luck everyone! Hope we will kick AI's ass out
 » 6 months ago, # |   0 God damnit I prepared this joke if i defeated AI : I defeated AI but Magnus Carlsen couldn't gg But there won't be a battle :/
 » 6 months ago, # | ← Rev. 2 →   +25 But the time 14:00 UTC, the 3 AI accounts have not yet registered this contest. I wonder if Alphacode will use them to participate the contests, or other account?
•  » » 6 months ago, # ^ |   +12
 » 6 months ago, # |   +28 What is Al? Please don't downvote it.
•  » » 6 months ago, # ^ |   0 Robot
•  » » 6 months ago, # ^ |   -9 Artificial Intelligence (technique that enables computer to think).
•  » » 6 months ago, # ^ |   0 In layman language, it's something that take a lot of other people code to train itself based on that it will generate it's code, just like how human learn to walk ,talk,etc.
 » 6 months ago, # |   +30 where are the bots ??
•  » » 6 months ago, # ^ |   +1 Humanity hails!
 » 6 months ago, # |   +30 Hello AI, where are U
•  » » 6 months ago, # ^ |   0 contest saint
•  » » 6 months ago, # ^ |   0 not today
»
6 months ago, # |
+215

It seems that AI is fooling us! It didn’t even register for the contest!

### What’s worse than AI beating humans is AI cheating humans!

 » 6 months ago, # |   +57 I remember for sure that there were AI handles here.... What happened? Is the uprising of the machines stopped? defeat of AI
 » 6 months ago, # |   +69 Did this announcement used to contain the misinformation that the AI bots from Google were going to participate in the round? Then Alexdat2000 realized that this is not true and simply erased it from the announcement without saying anything. Dude, come on, just say you were wrong
•  » » 6 months ago, # ^ |   +6 Come on, just scroll up a little bit or search on this page to see this comment.
 » 6 months ago, # | ← Rev. 2 →   +18 I hate speed-forces rounds like this -_- and huge gap of problems -_-
 » 6 months ago, # |   +45 Just solved B. after going through a lot of fucked up approaches. I would like to know what problem setter smoked when he thought of this problem. That thing must be good.
•  » » 6 months ago, # ^ |   0 And the position of B and C were reversed too for some reason. Kept trying B for a long time, then read C and solved it within 10 minutes smh.
•  » » » 6 months ago, # ^ |   0 Same here, it took me 10 minutes, very bad arrangement of the problems
 » 6 months ago, # |   +5 Weak Pretests for A.
 » 6 months ago, # |   +22 So you just added shitty constructive problems because robots were going to participate?
 » 6 months ago, # |   +6 Maybe at least AI would had fun with the problems.
 » 6 months ago, # |   +110
 » 6 months ago, # |   +24 Please explain the relevance of problem B?
•  » » 6 months ago, # ^ |   +10 confuse AI that is not participating
 » 6 months ago, # |   -11 After seeing problem B , i think writers forgot that this is codeforces and not atcoder
 » 6 months ago, # | ← Rev. 2 →   -29 Not sure why people hated B isn't that the most fun thing about problem solving when the solution isn't obvious and the problem author tricks you to think in a direction while the solution is out of the box
•  » » 6 months ago, # ^ |   +1 my solution doesnt even make sense, just xor all values and check for same parity. Bruh...
•  » » » 6 months ago, # ^ |   +8 yes because xor operations and plus operations gives the same parity as a result and that means bob and alice answers have different parity and it should be the one similar to the needed answer parity
 » 6 months ago, # | ← Rev. 2 →   +47 I really liked the problemset. One of the best div. 2 rounds, I have seen in quite a while.
•  » » 6 months ago, # ^ |   -28 Be ready for downvotes.
 » 6 months ago, # |   -9 I was so excited about AI competing with us, all in waste.
 » 6 months ago, # |   0 The verdict of interactive problem is super confusing. I get TL while it should be WA.
 » 6 months ago, # |   +4 Solution B was greatest anime betrayal.
•  » » 6 months ago, # ^ |   0 Damn right
 » 6 months ago, # |   +146 However, not about div2ABC, but about one certain type of problem I hate with passion (as a participant). You are given number and a set of arithmetic operations you can perform on it. Determine whether you can transform the number to another number.I see more than one operation, and my blood starts boiling. Honestly, the most artificial type of all problems. Look at me, I came up with 2304984092384 operations and stared at numbers to notice an obscure property. Now you find this property and forget about it forever because it's absolutely useless anywhere but this problem. Wow, so cool.
•  » » 6 months ago, # ^ |   0 SO TRUE
 » 6 months ago, # |   0 Speedforces
•  » » 6 months ago, # ^ | ← Rev. 3 →   0 Not really. It was of 2.5 hours
•  » » 6 months ago, # ^ |   +5 Well,I don't think so.I think Problem D is interesting,although it has some details.
 » 6 months ago, # |   +10 My approach for Problem D: Finding Zero Hint 1The problem indirectly asks you to print a possible $(min, max)$ pair. So, what's the significance of zero? Well, the $(min, max)$ pair might not be unique, and restricting the array to contain a single zero bypasses that issue. Hint 2Given 4 arbitrary numbers, $(a, b, c, d)$, can you eliminate 2 numbers such that we don't lose min or max? Note that we are not assuming that either $min$ or $max$ is unique. We just want to retain one copy of each. Do this in 4 steps. If you are not sure how to do it, refer to the sample, it has the entire logic. Hint 3Start with $(1, 2, 3, 4)$ and eliminate two numbers. Then, club the remaining two numbers with $(5, 6)$ and repeat. Similarly for $(7, 8)$ and so on.If the array is odd, the you can club it with any number that you've used before hand. You can also save one query if you track the previous queries, but that's not really needed, I think.The final retained pair would be the $(min, max)$ pair.
•  » » 6 months ago, # ^ |   0 My approach Write bruteforce to find the patterns. pattern finding bruteforcebool next_combination(vector& v, int n) { const int k = v.size(); int i = k - 1; int max_n = n; while (i >= 0 && v[i] >= max_n) { i--; max_n--; } if (i < 0) return false; for (v[i++]++; i < k; i++) v[i] = v[i - 1] + 1; return true; } void solve() { int n; cin >> n; vector v(n); for (int i = 0; i < n; i++) v[i] = i; vector c = {0, 1, 2}; vector> patterns; do { patterns.emplace_back(c); } while (next_combination(c, n - 1)); map, vector>> m; do { vector a; for (auto& p : patterns) { int mx = 0, mn = 1e9; for (int i : p) { mx = max(mx, v[i]); mn = min(mn, v[i]); } a.push_back(mx - mn); } m[a].push_back(v); } while (next_permutation(v.begin(), v.end())); for (auto& [key, val] : m) { for (int i : key) cout << i << ' '; cout << ": "; for (auto& vv : val) { cout << "["; for (int i = 0; i < vv.size(); i++) { cout << vv[i]; if (i + 1 < vv.size()) cout << ", "; } cout << "], "; } cout << '\n'; } }  Don't have enough time to code the solution. ...Profit!
 » 6 months ago, # |   +4 First you try to get clout with AIs then weak pretests, and stupid constructive problems.
 » 6 months ago, # |   +34 How bad could it be?Problem B: This bad
 » 6 months ago, # |   +6 Solved B < 15 min due to 'guessing' and 'pattern finding'. Seems like those bad guessing problems unless someone can give me a reasonable proof to solution.
•  » » 6 months ago, # ^ |   +1 If $a_i$ is odd, applying any of operations flips the parity, and if $a_i$ is even it won't change the parity. And since x and x+3 have different parity, you can get solution using number of odd $a_i$.
•  » » » 6 months ago, # ^ |   0 nice, btw the problem felt really weird. It was clearly pointing at the property b = x+3(cuz like why not b equal any random number) then tried some cases and realized the parity stuff
•  » » » » 6 months ago, # ^ |   0 Well,I think this trick is very normal. Whatever $b$ equals to,it is really easy to think about parity because of the fact that ⊕ and $+$ has the same parity.
•  » » » » » 6 months ago, # ^ | ← Rev. 2 →   +19 The way this problem statement is constructed it qualifies as april fools fun. Is this really what we want in usual contests?Edit: I show you what I wrote at minute ~10 in the contest, just before quit: /** * We obviously have to find some more or less "funny" observations. * It is kind of unpredictable if I find them in reasonable time or not. * So, basically I am out here. Sic. * * *** * However, what observations could be usefull here? * Something about x+3, why 3? * Can we simply find if Alice succeeds somehow and ignore x+3? * * Consider the last bit in y... * Why/How it is garanteed that exactly one of both gets y? */ void solve() { } 
•  » » » » » » 6 months ago, # ^ |   0 But if the statement is$b=x+1$or$\text{Alice chooses an odd number and Bob chooses an even number}$,the problem will be much easier.
•  » » » » » » » 6 months ago, # ^ |   0 Well, it is an easy problem. Trying to make it more interesting by obfuscating the problem statement is really, really bad style.
•  » » » » » » » » 6 months ago, # ^ |   0 What you said makes sense,but I think the problem creator just wanted to make the idea more hideen :) .
•  » » » » » » » » » 6 months ago, # ^ |   0 At least you liked it ;)
•  » » 6 months ago, # ^ |   0 You just have to see the parity. It doesnt matter if you add or do xor of any two numbers, if both are odd then after any operation they will be even. If both are even then then they will be even, else the result will be odd. So we just had to count the number of odd integers in the array and then use z or z+3 accordingly. Notice, that exactly one of them will be odd
 » 6 months ago, # |   +2 Nice round. I liked all problems even though I could solve only up to D. Btw how many problems did the AI solve?:))
•  » » 6 months ago, # ^ |   +6 Looks like zero... alpha zero.. =))))
 » 6 months ago, # |   +3 I don't know what to say about B, but i spent 1.5 hours and couldn't solve it at all :(
 » 6 months ago, # |   +1 The arrangement of B and C is not good, it took me 10 minutes to solve C and 2 hours trying to figure out how to solve B
 » 6 months ago, # |   +40 Don't know but to be honest ,these two guys(Alice and Bob) and their weird games have fucked me badly in my life than anyone else
•  » » 6 months ago, # ^ |   +3 Probably not two guys since Alice is a girl's name.
 » 6 months ago, # |   0 Disbalanced contest (B and C have to swap and really weak pretests for A)
 » 6 months ago, # | ← Rev. 2 →   +20 E is cute, I like how natural both the idea and the resulting solution are.A, C and D are pretty cool problems as well.B on the other hand is not a problem I like. It feels really really forced with the "It is guaranteed that on the jury tests, exactly one of your friends could have actually gotten that number". Also what even is the point of $x + 3$ instead of $x + 1$???
•  » » 6 months ago, # ^ |   +5 I thought the same about $x+3$, though I guess using $x+1$ would make the observation more obvious.
•  » » 6 months ago, # ^ |   +33 Trying to mislead AIs
•  » » 6 months ago, # ^ |   0 100% I needed more time because of 3 instead of 1 :D
•  » » 6 months ago, # ^ |   +30 Also what even is the point of x+3 instead of x+1Just to make idea about parity less obvious. We wanted to make $x^2-1$, but it made the problem ridiculously hard
•  » » » 6 months ago, # ^ |   0 Man if the authors really want to fu** with us they really can Lol
•  » » 6 months ago, # ^ |   0 Actually I compared first the ((x + a1 + ... + an) & 3) and ((x + 3 + a1 + ... + an) & 3) with (y & 3), which was wrong, but passed the first test. Than I checked ^ instead of +, and it didn't pass the first test. So I noticed the error and took 1 instead of 3.
 » 6 months ago, # |   +3 The only real programming problems (E and F) turned out to be too hard for me :/In E I guess that if one array has more than one occurence of certain number we can put half of them in L and other half of them in R, right?Problem A was great imo :)
•  » » 6 months ago, # ^ |   +3 It is correct, but it isn't necessary to solve it.See this comment for a rough description of one way to solve it.
 » 6 months ago, # |   +30 Spoiler
•  » » 6 months ago, # ^ |   0 lmaooo. idk why i laughed so hard at this lol
•  » » 6 months ago, # ^ |   0 We managed to scare it off this time =)))
 » 6 months ago, # |   0 I was just several seconds late for hacking a submission of Problem A. Basically when I finished typing the input, I got a message saying the solution had been hacked or resubmitted. Speed matters.
 » 6 months ago, # |   0 Codeforces is gradually becoming bitforces. I mean too many bit manipulation questions these days.
 » 6 months ago, # |   0 It would be funny if AI gets plag, AI not able to solve any question and then buying from telegram
 » 6 months ago, # |   +6 I hate pB.
 » 6 months ago, # |   0 I hope an open-source project is born and we get at least virtual participation of a bot in the future.
 » 6 months ago, # |   +4 Hence proved, humanity's greatest threat isn't AI but humans Itself :(
 » 6 months ago, # |   +18 I want to ask one thing, why would you create something shit like problem B, Instead just give an implementation problem or something else. What is so educative about this problem?.I don't like these kinds of problems where some people see some observation and get AC while others struggle. What skill do I lack to deal with these shitty problems?
 » 6 months ago, # |   +8 Problems A, C, D were interesting. B was very bad. E was easier(too obvious solution) for its position imo.
 » 6 months ago, # |   0 Any hint on E? (I came up with some greedy solutions but got WA)
•  » » 6 months ago, # ^ | ← Rev. 5 →   0 I believe it is max-flow. ( Didn't have time to implement and test it)Idea, find out which number of which array belongs to the Right segment.Therefore build a maxFlow graph: You have 1 source node, n nodes (for each array one), number-of-distinct-numbers-in-all-arrays nodes and the sink.You connect: each of the n-array nodes with the source with weight length of this array divided by 2 each of the n-array nodes with all the distinct number which ocurr in it with weight 1 (or if it occurs more than once, then a higher number) from each number node to the sink with weight "the total number of occurences in all arrays divided by 2" if the max flow is the half of all numbers in all arrays, the answer is true. and you need to read the flows to get the answer.
•  » » » 6 months ago, # ^ |   +9 You're on the right track with the graph modeling but it isn't max flow.Consider two types of nodes: Array nodes which represent a position in one of the arrays. Value nodes which represent some value. (There are at most $2 \cdot 10^5$ distinct values) For some position $j$ in the $i$-th array, we create an edge between the array node for this position and the value node for $a_{i, j}$.Let us consider marking a positon as $L$ to be equivalent to directing its corresponding edge towards the value node, and $R$ to be equivalent to directing it towards the array node.So now for $|L| = |R|$, we need in-degree $=$ out-degree for all array nodes. Additionally for the set to be balanced, we would also clearly need in-degree $=$ out-degree for all value nodes.This is clearly impossible if any value occurs an odd number of times since the corresponding value node will have odd degree, otherwise it is always possible.So we have a graph where every node has even degree and we want to find a way of directing the edges for in-degree $=$ out-degree. Remind you of something? SpoilerIts equivalent to finding the Euler tour of this graph.Be careful about the multiple edges.
•  » » » 6 months ago, # ^ |   +13 Unfortunately I think max flow is too slow :( . I tried several different implementations of max flow during the contest and they all TLE'd on test 3, and if you filter by TLE on test >= 3 on https://codeforces.com/contest/1634/status/E it seems I'm not alone.
•  » » » » 6 months ago, # ^ |   +3 I also had some thoughts on maxflow but based on the constraints I didn't implement it
•  » » » » » 6 months ago, # ^ |   0 Correct me if I am wrong, I think the complexity of Dinic on a bipartite graph is O(sqrt(V) * E), you have |V| = |E| = O(10^5)?
•  » » » » » » 6 months ago, # ^ | ← Rev. 2 →   +5 To my understanding, $\mathcal O(E \sqrt V)$ complexity is only achieved when the graph is a unit network. Despite this, I still figured flow was worth a try because it's well-known that max flow algorithms run much faster than their proven time complexities, and I've gotten AC on problems with bounds where it looks like flow shouldn't pass before.
•  » » » » » » » 6 months ago, # ^ |   +18 May I ask the reason why Qwerty1232 got accepted by this submission which using dinic (145470307). I think maybe he construct graph using Chunking. Amazing!
•  » » » » » » » » 6 months ago, # ^ | ← Rev. 3 →   +18 After reading that submission, I realized I had an unnecessary layer in my flow construction during contest! I've rewritten my code to fix that and now I get AC when using KACTL's push relabel implementation. Note that you still need a pretty good flow implementation, for example the Atcoder library implementation doesn't pass.Oh and I guess to answer your question about Qwerty1232's submission, I don't fully understand their flow implementation, but it looks like these lines: static constexpr double TL = 0.5; if (clock() * 1.0 / CLOCKS_PER_SEC > TL) { break; } play a huge role in letting the code pass. When I commented those lines out, the code TLEs. It appears they run standard Dinic's algorithm for 0.5 seconds, and then they switch over to an alternative dfs2 procedure that appears to just be naive repeated DFS with a visited array. My guess is because of how shallow the graph is, preprocessing good augmenting paths with a BFS isn't helpful and just takes unnecessary time.
 » 6 months ago, # |   -7 $B$ is more like a puzzle description than a CP problem. $y$ in the problem description is replaceable by an arbitrary even or odd integer without referencing the exact value. I think stating $y$ exactly as a way of distraction is not a good idea in a CP contest.
•  » » 6 months ago, # ^ |   0 yeah, but if they specified the parity, it would instantly give off a hint?
•  » » » 6 months ago, # ^ |   0 True, so this means that the problem quality itself is debatable, as it turned out to be just a distracting description masking a very simple problem.
 » 6 months ago, # |   +14 how can I see AI's performance in this contest ?
•  » » 6 months ago, # ^ |   +3 they seem not to have taken part in this contest.
 » 6 months ago, # |   +14 Once again, Alice and Bob screwed me over with their weird games. F*ck my life.
•  » » 6 months ago, # ^ |   0 I realy hate Alice and Bob!!!!!
 » 6 months ago, # |   0 My approach for D gets wrong answer on pretest 5. The idea is find the max difference for first 4 numbers (4 operations), use 2 more to find which of those 3 is not used, so I get min and max (call them p1, p2) numbers among first 4. After that, just iterate i from 5 to n, and do at most 2 operations for each one, first ask for (p1, p2, i), and if difference is higher, ask now (other, p2, i) where other is some position I know it's bad, and if I get the same answer, then p1 is not needed, so I update p1 = i, otherwise p2 is not needed, so p2 = i. Operations: 6 + 2*(n-4) = 2n-2. What did I do wrong?
•  » » 6 months ago, # ^ |   0 I did exactly that to get the same result :( https://codeforces.com/contest/1634/submission/145465061 Somebody explain
•  » » » 6 months ago, # ^ |   0 So my code fails for the array 2 1 1 2 0. The problem is it fails to give the min max pair for the first 4 numbers. I can't come up with a way to find the min max of first 4 numbers using only those. If you find a way, that should solve my problem (hopefully this was your problem too)
•  » » » » 6 months ago, # ^ |   0 Yeah I have the same issue, kept seeing 'allsame' variable in passed submissions, I get what that means now. Thanks!
 » 6 months ago, # |   0 Does anyone know what pretest 4 and 5 of problem D is?
•  » » 6 months ago, # ^ |   0 They are both max-tests. Test 4 has $n = 4$ and all combinations of $a_i \le 3$, and test 5 has $n = 5$ and all combinations of $a_i \le 2$.
 » 6 months ago, # |   -6 Meme
 » 6 months ago, # |   0 hello ai ，what about you？
 » 6 months ago, # |   0 I think AI-squad won, because they succesfully used misleading for them in problem B against human beings
 » 6 months ago, # | ← Rev. 3 →   +14 Damn! Too much bad pretests for Task A. This will cost me my Expert rank :))
 » 6 months ago, # |   +5 Me face when couldn't solve B because -3 % 2 = -1
 » 6 months ago, # |   0 I liked C, D and E but absolutely hate problem B and the pretests for problem A.Hit and Trial problems like B are just bad in my opinion and it becomes more luck based than skill based. No wonder why it has such less number of solves.A should have had more pretests. It was full of hacks and provided an unfair advantage (even huge advantages) to some participants who were able to hack solutions. Some participants even managed to get more points from hacks than by solving the problem itself.
•  » » 6 months ago, # ^ | ← Rev. 2 →   0 Why would you hate B? Hit and Trial you call it ? It's a simple problem on parity check. And C ? I find it funny that I guessed the solution for C that got Accepted. Absolutely loved problems D and E.
•  » » » 6 months ago, # ^ |   +3 The thing is, Problem is simple but people think differently. You thought about parity first that's why you got it in a short time, some people (like me) didn't think about this and played with various patterns and cursed the setter so hate is completely justified.
•  » » » » 6 months ago, # ^ |   +10 The only thing I want to say is, setter needs to be appreciated for such a wonderful problem or at least should not be hated. Just general suggestion, when it's div2 A/B and it seems pretty hard, maybe you need to "change your approach" is the hint :).
•  » » » » » 6 months ago, # ^ |   +10 I don't hate the contest. As already mentioned, I liked more than half of the problems that I tried and one problem doesn't make the contest bad. I have upvoted the contest blog. I only hate problem B simply because I didn't find it interesting and a little bit trolling (and looks like I am not the only one who feels so). Even A was not a bad problem but had some poor preparation.I always appreciate the efforts of the contest panel and I just wanted to express my opinion so that the setters may improve on such things in the future.
•  » » » 6 months ago, # ^ |   0 How would parity check cross your mind if not by hit and trial? Obviously, the most general way of approaching problems involving XOR is to go with individual bits and derive some interesting observation that way. But here, it was just about questioning why $x+3$ and why the additional constraint on the tests guaranteed to be having exactly one answer.And I liked the proof for C's solution. In my opinion, it was some very decent use of arithmetic progressions to make a very natural problem. (And as you can see from my username, I Love Constructives)
•  » » » » 6 months ago, # ^ |   +6 another way of looking at xor problems is even-odd.
•  » » » » 6 months ago, # ^ |   0 Let me show you another thought progress without guessing parity right away. It's also the thought process I had in the contest. First of all, XOR and ADDITION are nearly the same. XOR is ADDITION without carry. It is often hard to find easy invariants or algorithms for the carry, so I assumed, the solution has to be done without carry, since it is a B.The least significant bit is the only one not affected by the carry. So it seemed natural too look at it. Especially since x and x+3 have a different value on the least significant bit. Also the second bit, but analyzing the least significant one was enough to find a solution. Maybe for me it also helped, that I played https://nandgame.com/ not long ago and built a full adder.
•  » » 6 months ago, # ^ |   0 B looks like constructive from CodeChef div. 3 and that's why it's very pretty task. It doesn't necessary hard algorithms. Just a bit puzzling and that's all.
 » 6 months ago, # |   0 Can anyone explain how to even approach for B??
•  » » 6 months ago, # ^ |   +3 parity check
•  » » 6 months ago, # ^ | ← Rev. 2 →   +1 Look how $x$ and $x + 3$ differs and what $a+b$ and $a \oplus b$ have in common
•  » » » 6 months ago, # ^ |   0 okay gotcha thanks:)
•  » » 6 months ago, # ^ |   0
 » 6 months ago, # | ← Rev. 2 →   0 :v
 » 6 months ago, # | ← Rev. 3 →   -15 I think there were a few flaws about this roundProblem A: weak pretestsProblem B : cool problem but i think it requires more thinking than regular div2 B .Problem C: I dont know why this problem is even there .Just implementation based and a lot of cases(for me). Because of which was not able to read D+ problems.Didn't quite liked the round but it was a great effort by you guys. i genuinely hope we will get good contests from you next time. P.S. : i lost expert to this round phewwwwww
•  » » 6 months ago, # ^ |   +11 I strongly disagree about Problem C being "implementation based". There is a general solution that works for even $n$, and a small edge case to handle for $k = 1$. The overall solution isn't tough to implement at all — 145416321
•  » » » 6 months ago, # ^ |   +12 But do you really think it is of Div2 C standard ? i literally got the logic for it instantly ,on the other hand problem B was really cool. I guess swapping the positions of Problems B and C was not a bad idea .
•  » » » » 6 months ago, # ^ |   0 he was talking about the part, where you said it had a lot of cases, not about it's position.
•  » » » » » 6 months ago, # ^ |   0 I edited the comment ,happy now ?
•  » » » » 6 months ago, # ^ |   0 Hmm fair enough, I am a bit biased there since I solved B in around 5 mins whereas I took around 25 mins for C, but the solve counts seem to support your point.
•  » » 6 months ago, # ^ |   +12 lot of cases? n % 2 == 0: YES, print even and odd rows else: k == 1: YES, print one number on each row else: NO
•  » » 6 months ago, # ^ |   0 For C it was thinking up the proof that took some time, nothing to implement here void solve() { int n, k; cin >> n >> k; if (k == 1) { cout << "YES\n"; for (int i = 1; i <= n * k; i++) cout << i << '\n'; return; } if (n & 1) { cout << "NO\n"; return; } cout << "YES\n"; for (int i = 1, cnt = 1; i <= n * k; i++) { if (i & 1){ cout << i << " \n"[(cnt++)%k==0]; } } for (int i = 1, cnt = 1; i <= n * k; i++) { if (!(i & 1)){ cout << i << " \n"[(cnt++)%k==0]; } } } 
 » 6 months ago, # |   0 Problem F was somewhat straightforward if you have already solved 446C - DZY Loves Fibonacci Numbers. Why such a tight TL tho?
•  » » 6 months ago, # ^ |   0 IMO the TL wasn't tight. The linear model solution passes under half the TL even on Python, and a higher TL would allow for sqrt decomposition or segment tree-based solutions to pass, and increase the probability of some weird hashing-based solutions to pass (which has actually happened during the testing phase), which was not intended.
•  » » » 6 months ago, # ^ |   0 This O(n) solution got TLE because of its slow input method. Meanwhile, this O(nlogn) solution got AC. So I think the time limit and the data constraints are not so satisfactory.
•  » » » 6 months ago, # ^ | ← Rev. 2 →   0 Aha my bad, I assumed segment tree was supposed to pass. I just realized that it can be done in linear time.
 » 6 months ago, # |   +22 Lots of hate towards B, but even though I had the same issues as everyone (only solved it close to the end and after C), I don't think it's a bad problem.I don't think it's necessarily about some people seeing an observation about parity and other don't (although arguably it means some people do solve it much quicker).You could try computing the set numbers you can get with this process with brute force. In reality it's a huge set of numbers that grows exponentially with the input array size. Or is it? I didn't think too much about it, but I couldn't come up with a quick abstract argument why wouldn't it collapse just to a few numbers in practice, so I though it was quicker to write some code to check.Arguably it's a skill any competitive programmer is capable of (doesn't require you to have a specific bright idea about the problem), and a reasonable thing to do when you can't come up with a quick solution. Also it's useful for testing the correctness of more clever solution anyway.So the sim looks somewhat like: def sim(a: List[int], x: int): cur: Set[int] = {x} for c in a: nxt = set() for q in cur: nxt.add(q + c) nxt.add(q ^ c) cur = nxt return cur Then I tried generating random arrays a and initial number x, and seeing what I could get. If you inspect the set of numbers you can get, you'll notice that either all numbers in the sim results are even, or all odd, this is clearly a pattern.After trying it with x + 3 and comparing whether you get even or odd results, you essentially come to the actual solution.
 » 6 months ago, # | ← Rev. 2 →   +11 my submission Time limit exceed on testcase 178codeforces is too slow, AI lost to human
 » 6 months ago, # |   +3 What Happened did we win or loose??
 » 6 months ago, # |   0 My solution of D failed 10 times on 1000 random tests of n<=20 and it still passed system test. Wow. submission
 » 6 months ago, # |   -22 I didn't like the contest (I know authors have done hard work for this contest and I respect them for that.), at least the first problems were not good. D was interesting but wasn't able to solve it on time. Problems with the first three: 1. Problem A: It was a great problem A but the weak Pretests for the Case where the string is not a palindrome and k=1. I was able to hack 3 solutions but I think If I had time I could have hacked 3 more. It tells a lot about weak pretests ( I think this is a good measure). 2. Problem B: I don't think this needs an explanation. It took me an unspeakable amount of time to find the pattern. This could have been an ok problem C but it was not at all a good problem B. and not my favorite type of problem. 3. Problem C: First of all I loved this problem, whoever came up with this should get a raise. But the problem was a bit too easy for a C but apart from that, it was a good problem.
 » 6 months ago, # | ← Rev. 2 →   +6 I got sick and my brain overheated trying to solve problem B. I think it is another variant of covid
 » 6 months ago, # | ← Rev. 2 →   -8 Thought problem B was a bad problem when I solved it(Because I couldn't prove my solution and thought it was some random stuff) but when I saw the editorial and saw the observation that an odd XORing operation always inverts the parity of a number then it was very clear.So average problem I would say
 » 6 months ago, # |   0 The writers must have forgotten that B,C are for humans to solve.
 » 6 months ago, # |   +8 Why didn't AI take part in today's contest ? Are they scared ?
 » 6 months ago, # | ← Rev. 2 →   +16 Alternative approach for problem D, which guarantees solving in one fewer query (worst case 2*N - 3). (Submission here)Perform N - 2 queries of the type (1,2,j) for 3 <= j <= N, and note an index (not necessarily unique, but this is unimportant since ties can only occur at the maximum value, not at the zero) which gives the maximum query value. Call this best_idx1, and the maximum query value best1.Then perform N - 3 queries of the type (1,best_idx1,j) for 3 <= j <= N and j != best_idx1. This time call the maximum query value best2 and its corresponding index best_idx2.Then we are reduced to casework.Case 1: If best2 > best1, then we know that the maximum and minimum value pair is contained in the tuple (1,best_idx1,best_idx2), and we also know that it is not contained in the tuples (1,2,best_idx1) or (1,2,best_idx2). By elimination we see that the pair (best_idx1,best_idx2) will definitely give us the correct answer. Total 2*N - 5 queries.Case 2: If best2 == best1, then the max/min pair is contained in both (1,2,best_idx1) and (1,best_idx1,best_idx2). Since there is only one zero, we know that it is in both tuples, so we can safely return the two common elements (1,best_idx1). Total 2*N - 5 queries.Case 3: If best2 < best1, then we know that the tuple (1,2,best_idx1) contains the max/min pair, but that the tuple (1,best_idx1,best_idx2) does not. Therefore the answer cannot be (1,best_idx1), and therefore element 2 is definitely in the max/min pair. We need to determine whether (1,2) or (2,best_idx1) is the max/min pair, and we can do this by querying (1,2,best_idx2) and (2,best_idx1,best_idx2). The max/min pair is the first two elements of whichever query gives the greater result, and thus we have solved this case in 2*N - 3 queries.
•  » » 6 months ago, # ^ |   0 Same as your thought.
•  » » 6 months ago, # ^ |   +1 had the same solution. +1
•  » » 6 months ago, # ^ |   +9 Actually, in Case 3, you don't need to query (1,2,best_idx2), because you've queried that in the first pass. So, in total, there's only $2n-4$ queries.
•  » » » 6 months ago, # ^ |   +6 Very good point. A further improvement.I was lazy and didn't store the results of my queries but that does indeed save another query.
 » 6 months ago, # |   0 For Problem B, I just simulate two FST(Finite State Machine, like DFA in principles of compilers) consisting four status(00, 01, 10, 11) to search for some patterns when I can't figure out what problem writer's thinking. One of the FST is for plus operation, while another for xor operation.Maybe you can try this way to think about this problem, though I didn't notice the parity trick when I was in the contest.
 » 6 months ago, # | ← Rev. 2 →   0 Hello , I am new to codeforces and I appeared in this contest. I had a doubt with my code for the first problem . I dont know where do I post it. I have pasted my submission link. Can someone please help me figure out why did this not work?https://codeforces.com/contest/1634/submission/145446176
•  » » 6 months ago, # ^ |   +1 Hi, in the second for where you find a j that s[j]!=s[n-j-1], you need a break because you found that the string is not a palindrome, but in the next iterations you will set incorretly count = 1 if you find a j that s[j]==s[n-j-1].
•  » » » 6 months ago, # ^ |   0 Ohh Thank you so much
 » 6 months ago, # |   -23 Really poor pretest 2 in Problem A, so from the next time please try to make some strong pretest.
•  » » 6 months ago, # ^ |   0 Ok boss
 » 6 months ago, # |   0 How many problems AI solved?
•  » » 6 months ago, # ^ |   -8 It didn't participate.
 » 6 months ago, # |   +37 It seems that AlphaCode turned into AlphaPigeon
 » 6 months ago, # |   +8 Good contest(except pretest in problem A)
 » 6 months ago, # |   -40 downvoted for having B as bitwise problem + AI didn't participate
•  » » 6 months ago, # ^ |   +3 So just learn bitwise
 » 6 months ago, # | ← Rev. 2 →   -8 nice
 » 6 months ago, # |   0 Problem B was really tricky
 » 6 months ago, # |   +18 Congrats sus!!!
 » 6 months ago, # |   +3 when will the problems be given ratings? isn't it taking more time than usual?
 » 7 weeks ago, # | ← Rev. 2 →   0 Me : problem B from this contest is trash https://codeforces.com/contest/1688/problem/C : hold my beer