Hello / 你好，Codeforces!
We are really excited to invite you to participate in Codeforces Round 1112 (Div. 1) and Codeforces Round 1112 (Div. 2), which will be held on Jul/26/2026 17:35 (Moscow time).
For both division 1 and division 2, you will be given 2.5 hours to solve 6 problems in each division.
The problems were authored and prepared by aaa_Pigeon2, _MCYYDS_, 131241, Oken, and jhvjh.
We would really like to thank the following people for making this round possible:
- Error_Yuan for the great coordination.
- _istil and ukbwyx for optimizing some details of problems.
- tiger2005, StarSilk for black red testing.
- RockyYue, WangYuanyi, _istil, Portulaca, jason_sun, wangmarui, N_z__ for red testing.
- Watersphere, zac2010, _luqyou_, ukbwyx, cdx123456, Arpa, a_little_cute for orange testing.
- yllls, Fa_Nanf1204 for purple testing.
- 1234567890regis, qym110809, wusixuan for blue testing.
- ini_____ for green testing.
- MikeMirzayanov and KAN for the great Codeforces and Polygon platforms.
- You for participating in this round.
The score distribution is as follows:
- Div. 1: $$$750 - 1250 - 1750 - 2250 - (2250 + 1750) - 3500$$$
- Div. 2: $$$500 - 750 - 1500 - 2000 - 2500 - 3000$$$
UPD: Editorial
UPD2: Congratulations to the winners!
Div .1:
Div .2:
Auto comment: topic has been updated by _MCYYDS_ (previous revision, new revision, compare).
After commenting
., aaa_Pigeon2 is now setter! Good improvement!Actually, aaa_Pigeon2 is trying to farm downvotes.
I think aaa_Pigeon2 is cheater...
Show proof
Atcoder_official → Atcoder Beginner Contest 468 Announcements In that post, he said that his own Atcoder account was banned.
And so what? It could be a false ban.
I'm sorry, but all of the management will be much better than us and more careful. (For these issues), would it be easy to make a mistake in this situation?
Codeforces falsebans certain accounts if they perform too good at the start. I'm sure other platforms might have problems like these. Also, by your logic, you're a cheater.
Spectral::Cup 2026 Round 3 (Codeforces Round 1110, Div. 1 + Div. 2). All submissions for the div 2 part are skipped. Would you care to explain that?
I have never cheated. However, he already has a borrowed account, unlike me. Also, I have adequately explained and accepted the above, which is why this account remains.
Hey, it seems to me that tkdgkb is a master with master ratings and you're just Grey Newbie lol in common sense, is tkdgkb right?
His first account was falsebanned. Changing style to avoid misban and/or sandbagging is not against the rules in anyway. Also, if the codeforces staff truly believed that he broke the rules, his account would be deactivated.
" I have never cheated other than this account " Is that something to brag about? Because we all know damn well you're not supposed to make a new account after being banned unless you were falsely banned. You cheated (and just now openly admitted to it), and thus you wouldn't need an alternate account.
Also, where is the explanation for your cheating?
voltinary You're unrated. By your logic, why are you even having an opinion?****
I'm sorry but the translation seems to be quite wrong. I've never cheated.
First of all, tkdgkb is our club algorithm instructor. Also, I've already graduated from a lot of gifted schools. On the other hand, you're ignoring tkdgkb without knowing any context.
I'm sorry but the translation seems to be quite wrong. I've never cheated.
I'm sorry, what kind of AI did you use for translation if EVERY SINGLE SENTENCE got translated incorrectly?
QED.
i totally agree with u
Schrodinger's reply: You don't know who it's agreeing with until you ask
welp, looks like ur acc ain't gonna be kept after all.
ngl, i've been there fr. had another acc b4, but it got clapped right after i solved A–D in my first-ever div2. rip. but tbh i get cf's policy—it do be weeding out a ton of smurfs & dummy accs, innit?
ngl, i don't think u need a high rating to raise questions or debate on CF. but u keep using rating as ur main argument, which doesn't rly hold up. now, if we follow that same logic—since he's ur coach, then how come u've never participated in a single contest? and by that same reasoning, u'd have even less ground to speak, coz at least his rating is higher than urs. so that argument kinda contradicts itself tbh
Come to think of it, I apologize if there was anything rude. I've never cheated and I apologize to aaa_Pigeon2 for the misunderstanding. Don't do anything that lowers each other's ratings and enjoy codeforces.
Apparently, you are at top 3 of the Div1. You somehow beat Kevin114514 (till this point). I'm not accusing you, just saying facts.
And... This user is disabled.
bro I didn't participate in ABC468, but Atcoder banned me.
I'm so confused.
Fun fact: tkdgkb is a cheater.
If you search his name on Google, his yukicoder page comes up: https://yukicoder.me/users/24556/submissions
He used 4 or more different templates in the same contest, and his code shows clear signs of AI. And he somehow beat LGMs.
Right message wrong reasoning and sender
Good problems. As a tester.
I'd like to participate as a tester someday! I'll enjoy today's competition. Thank you to everyone for the questions!
Just curious, why did you remove your most recent blog post about Dominator Trees?
I read the statement of problem A and then left.
i 100% agree with you the best contest i've ever seen :3
As a Participant, hope this round gonna be fun!
As a participant, I will try to stay awake during the contest.
As a participant, I would like to solve more than AB
You will, good luck.
As a newbie who did solve abc I'm happy someone encouraging anonther fellow survivor and it made me feel happy so thank you
Me too. QwQ
I hope so too
Wish granted, you'll only solve BC
My bad, before the contest I overworked myself
That's really a good contest, as a tester, wish every participant can have fun! Good Luck!
Fast score distribution...
As a participant, orz aaa_Pigeon2
That's gonna be my first contest. Hope to do good.
As a writer, all my problems got declined by the coordinator.
So you can call me Li Shangyin because he's the author of the poem 'Untitled'. In China we call it 'Wu Ti', which can be translated into 'No Problems'. Isn't it interesting?
Wow. Insane problemsetter roster. Don't google "_MCYYDS_ AtCoder ban". Also under no circumstances read Nyaan's blog on how majority of "falsely" banned AtCoder users who appeal in CF blog comments are actually not falsely banned.
UPD. aaa_Pigeon2 is now also banned on AtCoder.
also aaa_pigeon2, definitely don't look at the Banned Account he has, or the Blatant disrespect towards the rules of Codeforces.
Now I understand why everyone is turning into ratist, because:
By the way, you’ll get to solve at least five problems written by me in each division.
One. cheating accounts get banned too XVIII, I never said you are not allowed to use the internet and would appreciate if you didn't twist my words out of my mouth, you were discussing during the contest which is against the rules of codeforces with other participants. Simple as that. But apparently you are too good for the rules, because "The rules don't apply to me when I get falsely banned!"
Quoted directly from your comment in which you directly disregard the rules and integrity of codeforces :>
"Since Codeforces banned my account without asking me anything first—which I do not believe was in accordance with proper procedure—I do not think I have any obligation to follow the first rule either.
...
Since the Codeforces staff themselves have concluded that I did not cheat, and I can also provide video evidence, why are you still wasting your time on this?"
Two. I also stated that blog about the "evidence" of TLE30 was bullshit. I don't see how anyone could've seen that post as actual evidence, considering Test Case 30 was likely a testcase intended to break slower submissions that were considered by participants.
Three. While you did provide a screen-recording, it's not 100% evidence of anything, due to the fact of other devices being possible to be present in the room.
First of all, you are mistaken about one point: XVIII was manually banned by the administrators after the contest, following protests from a large number of people. In contrast, I was banned during the contest without any notification, while participating in only my second contest. At the time, I was merely a newbie, and my ranking was not even particularly high—I believe I was only somewhere in the top 40. The only plausible explanation is that they thought I was using an alternate account.
Also, the prohibition on communicating with others should apply only to discussing contest problems and solution-related content, as the original wording says: “share ideas, solutions or hacks.” I believe Codeforces would agree with this interpretation as well.
What kind of evidence do you expect me to provide, and what evidence do you have yourselves? From my perspective, the coding styles of many other contestants do not look particularly human either. I do not believe there is any way to completely eliminate cheating in online contests, because even someone with strong offline results will still be accused and questioned.
So then what about your point here?
People misunderstand the rules. They do not even know that, in 99.9% of cases, only alternate accounts get banned. According to his demands, I am not allowed to use the internet—so how am I supposed to participate in contests?
Then why were you banned if you didn't have an alternate account? Really makes one wonder.
Because I performed very well in that Div. 3 contest—or rather, because that was simply my normal level, since I was yellow-rated on AtCoder at the time. Codeforces has become quite strict about alternate accounts, and accounts that are still at the newbie level but perform unusually well in their first contest are often treated as alt and banned.
If you still don’t understand, why don’t you ask Codeforces yourself?
So why was this account not banned? My guess is that my username is aaa_Pigeon2, which is obviously just aaa_Pigeon with a “2” added, and that I did a better job of deliberately underperforming in the earlier contests. Codeforces is generally less likely to suspect an account of being an alt when it already has a higher rating before achieving a particularly strong result.
sooo you admit to sidestepping the detection method designed to detect cheaters and admitting to sandbagging, but hey, rules don't apply to you when the website doesn't treat you fair, because everything revolves around you! (totally not a "life isn't always fair" thing you could've reached out to admins on and not broken tons of rules)
I never admitted to evading cheating detection. I only admitted to trying to avoid being mistaken for an alt account. Please stop misrepresenting what I said! I have been presenting evidence this entire time, while you have been trying to mislead others into believing your claims.
cheating detection also detects people who are sandbagging/smurfing by say, purposefully misrepresenting their solving ability, or general rule violations during contest, which obviously didn't work in this case. i never said you were directly cheating in this thread, I said you were sidestepping the detection but hey, because all you ever do is misrepresent my claims and provide inadequate evidence and incriminating yourself with more quotes that directly show you violating the rules of codeforces :/
“Cheating detection also detects people who are sandbagging or smurfing by, for example, deliberately misrepresenting their solving ability.”
What evidence do you have for this claim?The information I found says that “Cheating Detection mainly refers to code-matching or plagiarism detection, as well as AI-generated code detection.”
As for XVIII being banned, the fact is that Codeforces manually reviews some highly rated players near the top of the leaderboard, as stated here: https://codeforces.me/blog/entry/124418. The difference is that XVIII was actually cheating.
You are being disingenuous. Had he not "sandbagged", he would've been automatically banned (as you have seen with his previous account. And he would appeal it by... making a blog with a new account? (oh but multiaccounting is against the rules!)
Sandbagging is not against the rules and neither is changing style to avoid a misban. If what aaa_Pigeon2 has said is true, then what he has done is entirely reasonable. I think the only rule he has violated is creating multiple accounts, but that was after the first was banned (wrongly I might add). If you want to condemn him, your only complaint should be not contacting Mike after he was banned. After all, if you are wrongly banned, what should you do, quit CF?
Also, aaa_Pigeon2, you using the internet is allowed and you can even use a search engine, but your code isn't allowed to, so you have not violated this rule at all!
Plz stop this cinema, and wait to enjoy this round.
And about the original wording in the rules regarding “not being allowed to use the Internet”:
"It is prohibited to access the network, attack system security, work with filesystem, try to hack the judge and etc."
Honestly, I don't think this rule make sense.
I think the intention of this rule is that you can't submit code that accesses the internet, e.g. connecting to a local server and dumping the test cases.
This rule is also from a very outdated version of the codeforces rules, and shouldn't be treated as authoritative.
The original accusation was disorganized and not very reliable overall.
Even so, I strongly believe that some of the people named in it were cheating. (This does not include "aaa_Pigeon2".)
Let's look at a few of the submissions.
The first example is from a gray Codeforces user from India. They did not even remove comments that appear to have been generated by AI.
Nischaya008 (reportedly banned from Codeforces)
The second example is from a red coder who was reportedly banned from AtCoder.
RockyYue (reportedly banned from AtCoder)
The next example is from a Legendary Grandmaster.
NanYan
XorGhost
FLY_lai
There are only so many reasonable ways to write this kind of routine.
Even so, it is unusual to see so many submissions with almost the same structure.
It is even harder to dismiss this as a coincidence when several of these users have already been banned or widely accused of cheating.
For these reasons, I no longer believe Codeforces can become a fair and trustworthy place for competitive programming again.
Nice comment!
You put the main point of my previous blog in a clear way.
A year ago, I already predicted that cheating in cp would skyrocket because llms would get cheaper and more advanced. Most cheaters do not have access to $20 models and use free versions. In 2026, those free versions are already enough to solve some 2400-rated problems. In the future, there will be no problem that cannot be oneshotted by a $20 subscribed llm. So it will be practically impossible to detect smart cheating by only looking at a user's output code.
Btw, I did not delete my blog — it got deleted by admins, and I received a 2-day ban. With that said, I will stop practicing on codeforces and continue doing contests only on atcoder before it gets overflown by cheaters too.
Exactly, every competitor you mentioned is a cheater. If their performance is better than yours, it must be because they're secretly using AI.
Even if they have competition results to prove themselves, they can't escape suspicion of cheating. Once they support each other, it's definitely them colluding and making excuses.
You must be the embodiment of justice!
I’m not arguing with a guy who defended a confirmed cheater and who is top 4 in a round where C2 & F can be solved by free chatgpt.
You guys think downvoting comments about cheaters is going to help you. But atcoder already proved my point by banning the pigeon guy.
Get lost, cheater.
Yes, you are right.
It's true that before the contest, the problemsetters leaked the difficulty of the problems in a group of 2,000 people and didn't carefully check whether the problems already existed. I hope they won't harm contestants again in the future.
Regarding your accusations that these two problemsetters, thomaswmy, and I cheated, I want to clarify: thomaswmy is a gold medalist in NOI2026 and has already secured admission to Tsinghua and Peking University. aaa_Pigeon2 and _MCYYDS_ are silver medalists in the China region of APIO2026. Their performance in the online contest matched their performance in the offline contest.
If you really think they cheated, please provide detailed evidence showing why their coding style and coding speed are unusual.
I didn't defend yangchang(also known as atgc in Atcoder) in that announcement post. At that time, the entire OI academic group didn't believe yangchang had any motive to cheat. Because Atcoder has a precedent of wrongly banning users, I asked Atcoder officials about yangchang's situation and later received a response.
I didn't win any good awards in the offline competition, so I don't have the right to justify myself for that.
About why I performed poorly in these two contests: First of all, I want to clarify that this account has always been my main account. In the first contest, I solved problems D, B, and A in that order, but then I was mistakenly banned by Codeforces, which prevented me from finishing the contest. Later, I appealed and got it unbanned through my alternate account LGMS_sfls2029. In the second contest (which started at 10:35 PM UTC+8), I left early because I was too tired from not sleeping well in the afternoon. The two contests I participated in afterward were at times that were relatively friendly for Chinese.
My English is poor, so I used a translation app. Hope you don't mind.
I agree with you that thomaswmy is most likely not a cheater. He wasn’t in my initial list; I added him before posting the blog, which is why he was last on my list. You can see that his TL 30 submission is different from the usual ai-style submission. My main suspicious point against him was that he solved F in 6 minutes, but that can be explained by parallel thinking while attempting E.
The two other guys you mentioned won silver medals at APIO. IGM lvl is enough to win ioi gold. You can’t tell me that ioi gold < apio silver
mem0ry: IGM lvl is enough to win ioi gold.
Maybe he's right, because in countries strong in OI, the bottleneck to getting an IOI gold medal is getting into the national team.
hello, mem0ry, can you help me check if ricefruit has ever cheated in a competition?
Okay, let me reveal my methods of exposing cheaters and try them on the person you mentioned. Sometimes my comments may seem unhinged and unreasonable. I just dont want to write an essay about every cheater.
His performance shows no anomalies. From the start, he has been showing great skills. The only questionable round is Goodbye 2025, which can be explained by rage-quitting after failing to solve D. But, on the contrary, the person who was arguing with me has two blue performances and one lgm performance in a span of two months. (Newborn Newton???)
He got AC for 2067E on the first attempt. He solved it using lazy dp (which differs from the common AI solution). Furthermore, he spent more time solving F than E!
He solved https://codeforces.me/contest/2116/problem/E in one attempt. As far as I remember, this div1 C was an implementation heavy problem and was hard even for gpt pro back then.
Overall i don't see signs of ai use. He is most likely legit.
Fun fact:LGMS_sfls2029 is the alt of 16777mt16,which he used to appeal after getting misbanned from CF,that why he said "Yes, you are right."
joker
thief
There's a Chinese saying that goes, '贼咬一口，入骨三分。(It's really hard to defend yourself when you're falsely accused by wicked people, and the harm can be huge)'. You know what I mean.
Exactly—everyone is cheating!
Their code uses different variable names, different sorting methods (
rbegin()/rend(),reverse,greater<ll>(), reverse indexing), and even opposite boolean conventions—but their ratings are higher than yours, so they must be cheating. Airtight logic.What a great logic! they used different variable names, wrapped the sort and unique in different
ifs, have different styles (space v.s. no space, etc.) but they are ALL cheaters because you believe so.Following your logic, I would like to inspect your code(379920310) for 4A - Watermelon.
Isn't this IDENTICAL to the following code by Haneen_Mohamed11 (Not mentioning this user because I don't want to disturb someone unrelated):
Following your logic, I believe it's resonable to say that this is your alt.
Oh wow, did you ever actually learn what prime factorization is? Because that's literally the most standard way to break down a large number. There's no "creative" way to do it — it's math, not abstract art. And your whole "there are only so many reasonable ways to write this routine" argument? Cool. Then name one. Just one. I'll wait. Oh, and accusing people of cheating just because they slapped #include <bits/stdc++.h> at the top? That's not evidence, that's just you not knowing how competitive programming works. It's a boilerplate include. It's like getting mad at people for writing int main(). Grow up. This isn't even the hard part of the problem — it's literally five lines. Maybe take a step back, learn something new for once, and then come back when you realize the whole world isn't conspiring to cheat against you. Spoiler: they're not. You're just not as special as you think.
Did you make this up
I think this can be reasonably inferred. After all, cheating rarely results in an account ban—otherwise, there would be no point in having the “skip” penalty—whereas if the administrators believe that you are using an alternate account, they ban it outright.
did the war end?
No
I'm also a victim in alt banning.
We don't have any other fault except using alt accounts.
Using alt accounts is against the rules, how dare you call youself victim?
First. I believe that their bans are false bans because they do not have the initiative to do so. After all, they all have GM or IGM skills(demonstrated by native offline contests which are guarenteed to be fair), using AI probrably even degrades their performance, why would they do so?
Second. Being banned(outrightedly or falsely, nevermind) doesn't stop them from comming up with good problems. After all, the codeforces staff did review their problems.
Third. Whether somebody is banned or not is none of your busuiness. If you don't want to participate, then leave. But why did up their pasts?
(probrably some typos in the text, but I think you can get what I mean).
If you want actual, convincing proof, feel free to talks me and pick any upcoming Codeforces round (Div. 1 or Div. 2, doesn't matter). I'll screen-record my entire contest and send it to you. But if you just want to accuse me without evidence, go ahead and do whatever makes you happy.
Translated from Gemini.
First time I've seen announcement blog get downvotes, what's happening?
Some of the problem authors ALLEGEDLY cheated
I have quite a lot of trust in AtCoder that I don’t have in random cheater expose blogs, so yeah idk. I won’t be able to participate anyway since I will be hundreds of miles away from my pc lol
with that being said, I would not blindly say AtCoder is perfect — it is possible that the two cases that maroon and Nyaan posted were special and that AC does indeed false ban sometimes. Still, for a platform as respected as theirs I bet there will be good evidence and chance to appeal.
I think one thing has nothing to do with the other.
Now I'm not sure whether the authors have cheated, but what's the matter with the problems they wrote? Can the problems let the cheaters pass but reject others? That's crazy bro
So just participate is enough:)
Ya good point. I just can’t cuz I’ll be at conference lol
As a tester, give me upvote.
By the way, _MCYYDS_ is very strong!
orz wusixuan
orz wusixuan and _MCYYDS_!!!
As a tester,I'm too weak to offer any useful suggestions.
And sto aaa_Pigeon2 orz
And I can't speak English well.
And good luck and have fun.
ukbwyx orz
orz
are we only allowed to take this in the time window 10:35 — 1:00 pm to earn rating?
In fact, I actually had a chance to change this (like moving the start time to 8:35 p.m. or 7:35 p.m. in UTC+8), but I completely missed it when the coordinator reached out to confirm :(
Hey, that's a big thing to miss! But it's okay, as we're all used to the late timing.
Is it really that easy to change the time? I don't think so, if some problems of this round or the whole problem set is used somewhere else then I think you can change time.
Yay, like rain after a drought
Maybe this contest help me to reach Specialist.
No interactives :(
No interactives :)
Auto comment: topic has been updated by _MCYYDS_ (previous revision, new revision, compare).
orz ckx
My first time for CF rounds QAQ. GL!
As a tester, give me upvote.
By the way, aaa_Pigeon2 is my friend, he will AK IOI!
The act of setting problems has virtually nothing to do with cheating. Besides, the coordinator is responsible for ensuring the quality of the contest. Some people are simply trying to use questionable—and most likely invalid—allegations of cheating as a pretext to attack the entire contest.
Upvote me
downvote me
As a tester, I like the problem of this contest
That's gonna be my 11th contest. Hope to do good.
Dammmm!!
The Affiliated High School of SCNU???
dsadsadsa
there is no Russian translation...
Russian translation is buggy ig.. Sometimes it appears after reloading the page.
Somehow the problem statement of C in CF is different to the one in m1 of CF? It stil means the same tho.
it is not working unable to open question?
use m1 CF
Task D has the different descriptions on the main site and the mirrors.
Main
0 1 1 0 2 -1 -1 0 2 1 3 2 1 3 0 1 3 0 2 3 0 2 1 16 0 1 2 3 1 0 3 2 2 3 0 1 3 2 1 0 144
Mirror
0 1 1 0 -1 -1 0 2 1 3 2 1 3 0 1 3 0 2 3 0 2 1 0 1 2 3 1 0 3 2 2 3 0 1 3 2 1 0
The pretest 1 for A is also different to the sample test of CF main site. It is similar to CF mirror site tho.
i give up
Loved the Problem Div2 D / Div1 B, especially the logical deduction for definition of v(i).
Counting Permutations <<< Observing Cases For No Permutation.
I hate construction problems so much. Drained me this contest.
Anyone has tips to get better?
My issue is i do not know how to begin construction and interval/range problems. and i am a loyal fella so i do not skip my questions for the next one.
Div. 1 Problem F solution: https://codeforces.me/blog/entry/63630?#comment-475048
Any thoughts on solution for div2.E?
$$$E2$$$ was quite hard. My code for $$$E1$$$ passed $$$55$$$ test for $$$E2$$$.
Me when $$$E2$$$ had $$$54$$$ more test:
Solved D at 02:26:42, 4 minutes left to go, phew! got idea last 15 minutes.
Problem D1A~D were good, but D1F was a well-known problem.
bruh how 1.5k solves on $$$D$$$?
Even this fact can be digested, I am just surprised that how come we have Div2 participants solving Div2F in 8-15 minutes!
Also, why are you smurfing? This is your main The_Mad_Max
Seem because he was highlighted by "CF Cheater Highlighter" extension
im so pissed TLE35 on E1
Solved Div2 D in the last second ;)
I did so bad on A and C tho :(
Chinese can fly!!!!!!!!!!
Is it just me or problems are exceptionally terrible? I cant see any of ABCDF (dont know about E) being accepted by coordinators in recent times. Sorry if it is rude
I thought C was nice even though I bricked it for an hour
F is bad, but what's wrong with ABCD in your opinion? I have not pre-reviewed or otherwise participated in the preparation of the round or tried to solve the problems. I just looked at the statements and solutions now, and they seem... reasonable. Value your opinion, so would love to hear a more detailed review.
Sure! I will admit that "exceptionally terrible" was an over-reaction right after contest, but still I have something to say.
A: Solution in 2 steps: 1) iterate on m 2) greedy of type "find subsequence t in s". I think both of those steps are very not novel, and their combination is not interesting too. Feels like a problem that is being recycled for like 100th time. Much lower quality than the bar set by CF Div1 rounds.
B: Tbh, I was biased towards this problem right after contest (because of getting 3 WAs of a_i=n case). Thinking about it now it is actually not that bad. Again 2-step solution: 1) figure out there are O(1) options for positions of N, and iterate on them; 2) combinatorical thing of counting ways to put objects in spots, where valid spots for every object is a prefix of spots + figuring little details. Step2 is not fresh, but Step1 is actually alright and somewhat interesting. Still overall problem is just not my cup of tea, but trying to be more objective: it is alright.
C: My main issue with this problem is asking for 2 blocks, and not arbitrary k blocks. I am biased because of the way I was solving it in contest, but what happened is: I spent a lot of time trying to think how to use a structure of 2 blocks, like thinking backwards and trying to find some nice properties. When I dropped this path and tried to solve for general k, it did not took a long time. Seeing solutions, everything seemingly can be generalized for k by just changing 2 to k in code. Therefore it feels like author decided to use 2 not k only to trick contestants into trying to think about something nice, while the solution is more or less standard DS story, and it is pretty annoying. Of course in general, problemsetting technique of specifically choising some substle case of problem, while solution is more powerful is fine, and I remember examples where it was reasonable. Here it just feels cheap and annoying to me. About solution: again 2-step 1) think of counting blocks as counting "x is in, x+1 is not" 2) apply DS. Of course step2 have more in itself, and it is totally normal for DS problem, but Step1 again is very not fresh, and I'd like for DS problems to have something more interesting in it before, well, applying DS part. Still feels much lower quality than usual bar.
D: Ok, here I was definitely wrong, because of my overcommiting to solving problem in a stupid way of "write bruteforce and look for patterns on paper" (thanks icpc practise) instead of trying to go intended way. Editorial solution is definitely alright and motivated enough, so that it is very possible to solve without brute. It is not ideal that problem can be solved pretty easily by monkey way, but it is acceptable.
Overall: AC I don't like, BD are actually more or less alright
I had the same 2-block thought during the contest, would've also prefered 0-block tbh. but anyway, isn't it maybe to trick on purpose?
I assume it is on purpose, and I dont think it is particularly motivated and nice in this case. Maybe I am just mad because of being tricked though
Chinese can fly! Chinese can fly! Chinese can fly!
someone tell me how to do div2C, like what did i miss :+
You can check whether a subsequence of length $$$L$$$ is possible or not in O(n) time
The number of elements to the left of $$$a_j$$$ is $$$j-1$$$. By this logic, if the number of elems in the left is $$$nl$$$ and number of elems in right is $$$nr$$$ then for each element ($$$nl \lt l-1$$$ or $$$nl \gt r-1$$$) and ($$$nr \lt u-1$$$ or $$$nr \gt v-1$$$)
So if u wanna check if a subsequence of length exactly $$$L$$$ is possible or not, u can do it greedily (i.e iterate over every element in the array and choose the first element which satisfies ($$$nl \lt l-1$$$ or $$$nl \gt r-1$$$) and ($$$nr \lt u-1$$$ or $$$nr \gt v-1$$$) and adjust $$$nl$$$ and $$$nr$$$ accordingly)
Greedy works cuz if $$$a_q$$$ and $$$a_p$$$ both works and $$$q \gt p$$$ then if we choose $$$a_p$$$ initially then later we can either choose $$$a_q$$$ or not but if we do the opposite, we loose a chance
Now that we can check for length exactly $$$L$$$ in O(n) we can do a O(n^2) soln by checking for n,n-1,...,0
Great explanation...
Even I wasn't able to prove greedy during contest and kept bumping my head on DP + BS solution... Thanks for explaining..
Thanks sir:)
orz exchange arguments
Good contest, i will code more
ratings updated
Congratulations with GM
orz
Auto comment: topic has been updated by _MCYYDS_ (previous revision, new revision, compare).
Thanks for the round; the problems were very interesting and creative. It's a shame, though, that the second task didn't involve DP.
can yall round the ratings up rq ty
solved D but didn't solve C... (Div.2)
I thought of the enumeration length, but I didn't think of how to determine it within O (n).
I am currently writing a solution to the E1.String (Easy Version) Div 1 problem. I have written a solution here: https://codeforces.me/blog/entry/155533. I would greatly appreciate any feedback or better suggestions.
Did anyone notice that it is 'Editoral' instead of 'Editorial'?
Hello Codeforces Team, I would like to respectfully appeal the plagiarism flag on my submission for problem 2250F, in the Contest named Codeforces Round 1112(Div.2). I solved this problem entirely on my own during the contest. I did not copy code from anyone, share my solution with anyone, or use any external source or communication with other participants while solving it. I understand that your plagiarism detection system identified a significant similarity with other submissions. However, I genuinely believe this is a false positive, as my solution was independently developed. If required, I am happy to explain my approach, the reasoning behind my implementation, or provide any additional information that may help with a manual review. I kindly request that my submission be reviewed manually. Thank you for your time and consideration.
Sincerely, adicodeforces
I would like to respectfully appeal the plagiarism flag on my submission 384416396 for Problem 2250D in Codeforces Round 1112 (Div. 2). I received the email stating that my solution significantly coincides with another participant's submission. I fully understand the importance of maintaining fairness in Codeforces contests, and I appreciate the efforts of the moderation team. However, I sincerely believe that this similarity is a coincidence. I developed my solution independently during the contest and did not copy code, share my solution, or use any unauthorized assistance. To support my claim, I am willing to provide evidence of my independent work, including: My code editor history showing the solution. My handwritten rough work and notes that I made while solving the problem. A detailed explanation of my approach and implementation, if required. I respectfully request a manual review of my submission before any final decision is made. If there is any additional information or evidence that would help in evaluating my case, I would be happy to provide it. Thank you for your time and consideration. I appreciate the work you do to keep Codeforces fair, and I hope my submission can be reviewed in light of the evidence I can provide. Sincerely, dhruva.7
lol
It's a shit contest with shit authors.
AHH I still need practice... I'm still a newbie QAQ
Auto comment: topic has been updated by _MCYYDS_ (previous revision, new revision, compare).
Auto comment: topic has been updated by _MCYYDS_ (previous revision, new revision, compare).
Can someone explain the downvotes
Because this round have too many mistakes.
Why it is -402 now?
Why so many downvotes ?
So many dramas around this round!
-500
The contribution multiplied by -1 exceeded jiazhichen844's NOI score just now.
可能还是应该支持一下国人吧
Why are there so many downvotes for this blog?
Why so many down votes? Now it is -576.