Hello, Codeforces!
We are excited and pleased to announce that Codeforces Round 1075 (Div. 2) will be held on Jan/23/2026 17:35 (Moscow time). This round will be rated for all participants with rating below $$$2100$$$. You will be given $$$2$$$ hours to solve $$$6$$$ problems and some problems will be divided into subtasks.
The round is based on the Sharygin International Geometry Olympiad All problems were authored and prepared by yanb0, furt1ve and me.
We would like to express our special thanks to:
- Akulyat for coordinating the round and assistance in preparing problems;
- the testers: Wansur, __baozii__, k1r1t0, Mark_Pr, _istil, OG_Matveychick1, TimDee, zhenja, abs0lute, princeee, NotDWT, Sokol080808, machine_solution, Pobe, madlogic, wuhudsm, pattern-seeker, dvb1r, VitaliiV, penwick, sanya37y, itz_pabloo, Morselllprimo, AK_15, Golden_Square, Norman165, arsen1y, graphs_enjoyer, tih-a, emirhanbanan, ak1ko, s97b, thereverberation, bibiq for their time and effort in testing the problems;
- MikeMirzayanov and KAN for the great platforms.
The score distribution is below.
$$$500-1000-(1250+750)-(2000+750)-2500-3250$$$
GLHF!
UPD1 The round is over, thank you for participation.
UPD2 Editorial
UPD3 Winners and First to solve
Div2
| Place | Participant |
|---|---|
| 1 | Timmyliuyunxi |
| 2 | mainkkk |
| 3 | Suzt_ilymtics |
| 4 | RaresPoinaru |
| 5 | bookpig |
Div1 + Div2
| Place | Participant |
|---|---|
| 1 | StarSilk |
| 2 | Rubikun |
| 3 | ksun48 |
| 4 | potato167 |
| 5 | kotatsugame |
First to solve
| Task | Participant |
|---|---|
| A | i_hate_pahadans |
| B | 300iq |
| C1 | thaibao08 |
| C2 | Codfish |
| D1 | porzlck |
| D2 | YuukiS |
| E | Baskot |
| F | GoatMessi30 |
As a tester, give me contribution
Fun fact: the round was prepared by school students
strong 💪
Nice!
Damn!
School students of today's time are much worth and intelligent.
салют всем своим) раунд будет получше, чем рег, уверяю вас. gl to everyone!
Is the person in the picture in the announcement?
As a tester, https://youtu.be/dQw4w9WgXcQ?si=9l7Xy-tIMOu0pzc1
knew it was coming
YouTube ads saved me
as a tester, i can confirm this round is based
As no one more than a simple participant, gl to everyone
Hope to become expert again:)
aha, I used to see you on LeetCode often. You can definitely make it back to blue.
Thanks.
Maybe you're also in the group 0x3F club?
is there any group add me
Capybaraaaa
I hope this competition suits me better and helps me become a candidate master.
What does "The round is based on the Sharygin International Geometry Olympiad" mean? Oh no, I'm really bad at computational geometry.
Is the contest heavily focused on geometry problems? T.T
As authors, we avoid spoiling the problemset in any way. The strikethrough text is a joke, you can safely assume that the expected value of the quantity of geometry problems is the same as for any other Codeforces round.
that's what a geometry problem contest author would say
No leakage in this blog… https://mirror.codeforces.com/blog/entry/139173
lol nobody understands the joke / what happened in that link (it ended up being all geometry problems, and the blog picture shapes lined up with the questions in order).
capybara
hello
capybara.
yay
I hope it goes well.
Thanks to the authors and testers for the effort! Looking forward to the round, GLHF everyone
I hope I become specialist after this contest
Good luck to everyone!
Thats not how ratings work
what do you mean?
He says, that thats impossible that everyone will get +delta. Only +0, but we should sync and say who will solve AB, who A, who ABC. If you get +30, that means someone will get -30(not 100%). He wants to say, that when someone wins, someone other loses. That impossible that we all will be winner. (Sorry for bad English, i tried my best).
Sorry for any confusion but I just want to wish everyone good luck! Anyways, hope it will be an amazing contest.
Ooh i understand now, thanks for the explanation
Capybara Capybara Capybara :)
I hope the round will not
be based on the Sharygin International Geometry Olympiad.We hope that it will be based
on the Sharygin International Geometry OlympiadCapyborus
as junior, it will be agood practice
Stuck between 1000 — 1010 for a month. Hoping to get a goode positive delta so that I can reach pupil fast.
Your pfp somehow reminds me of Shadow Fight 2. Man what a game it was!
Another hope.
As a tester, this was an unexpected penguin pfp meetup
As a tester, these guys have cooked. GLHF to everyone!
Last Div-2 promised world peace. This one will make sure it prevails☮️
GLHF
we are in Iran. please help us
Good luck everyone!
Good luck guys
Hope my rating can reach 2000 by this contest!
how can i be a tester??
when will the score distribution with number of subtask be shared
I hope I hit pupil after this round.
Thanks for the announcement! Geometry-based rounds are always interesting and challenging. Looking forward to the contest. GLHF to everyone participating!
Hope for another 1750 D :)
Is using yuantiji allowed by codeforces rules?
how does people get selected to write contest or become testers?
The score distribution will be announced later.
when will "later" come?
I want to be a specialist... I am currently suffering a great pressure on this division 2 contest.
As a tester, https://youtu.be/dQw4w9WgXcQ?si=9l7Xy-tIMOu0pzc1
score distribution?
Has the score distribution been announced?
"The round is based on the Sharygin International Geometry Olympiad"
Don't say you weren't warned
could someone give me a sheet of tissue? Because I feel that I want to cry
Will the score distribution be released within the next hour?
When score distribution?
GLHF everyone!, also just a quick question, how do people get to be testers? I'd love to contribute to the platform more.
Testers are basically friends of the main guys
woah, suddenly makes so much more sense lol, better make more friends on here. wanna be my friend?
The score distribution is released
OH NO Geometry, here we go again!
king kong ain't got shit on me
D1 will be tough nut to creck
Good luck guys! Hope to make it to expert.
Amazing performance!
Thanks!
The problem statement of B2 is really BAD,the problem itself is fine,also so many solves on D1 lol.
you mean C2 :\
Best round imo
AM I NOOB OR WAS THIS HARD AF? :(
I hate constructives.
Such a badly written contest (not problem wise).
Doesn't greedy work for E or is it my bad?
Yeah i also thought of a greedy solution but didn't have time to validate or code it
I checked some of the accepted submissions and greedy works but I couldn't pass it because of my poor imp skills T_T
wtf problem B is ...very bad problem statement for B
100/100 to the problem framing of B, spent nearly half an hour to get what was written exactly.
same:(
I didn't understand till now what problem is.
somehow misread every single problem
Should have tried to solve D1 first . Was able to solve till C2 but due to scoring distribution did not end with good rank
Auto comment: topic has been updated by Akulyat (previous revision, new revision, compare).
I saw this one user omdutt2004,
looks very sus, cheating since many contests, reported many times but still not banned, cheated today too !!
for B, why the first one passed but the second one didn't?
passed
WA on testcase 9
Maybe because of precision issue while using ceil,
Personally i found C1 much easier than B
Fun contest, especially C1/C2. I just guessed random strategies until I found one that works locally for both even and odd numbers in a reasonable amount of time.
Can you list some of the strategies.
By strategies I really just mean varying the value of $$$p_n$$$ and deciding how to try for possible values of $$$j$$$ (do we go up from $$$i+1$$$ to $$$n$$$ or down from $$$n$$$ to $$$i+1$$$, assuming we choose the first valid value for $$$j$$$?) Some strategies were either too slow or didn't generate a permutation when one existed.
I ultimately found that for C1, choosing $$$p_n = 1$$$ and going down from $$$n$$$ to $$$i+1$$$ works. For C2 it was slightly more complicated, I ultimately found that choosing $$$p_n = 1$$$ for odd $$$n$$$ and $$$p_n = n - 2$$$ for even $$$n$$$ works, going down from $$$n$$$ to $$$i+1$$$ in both cases.
I don't know why my solutions work, but I intuitively felt that a possible strategy like this could work and it would be much faster to brute force a strategy by trial and error than to actually "solve" the problem.
If you're really interested my screencast is here, I work on C1/C2 from 34:00 to 1:00:00.
I think E is much more easier than D2.
In fact, E is much easier for being E
Anyways, good problem
I think, I missed E due to just one 'if' statement :( .
E was quite quite easy. it should have been C problem.
darn it :( . Got AC after adding one if statement.
https://mirror.codeforces.com/contest/2189/submission/359456933
I am curious about the note of the problem B.
Before the update of the statement, the note of B is:
"In the sixth test case, the frog can reach point $$$10$$$, for example, as follows: jump $$$6$$$ times using type $$$2$$$ and $$$1$$$ time using type $$$1$$$."
I used 20 minutes to seek where is the 2nd type of jump, and the 6th case of the sample is
and the meaning of $$$n$$$ is "the number of types of jumps".
The announcement of the statement of B was updated didn't refer this change, and when I asked about it I just got "no comment" after I have sent it 10 minutes.
I can only say that this statement is a complete disaster.
I spent about 15 minutes just finding out what “type of jumps” actually meant, and another 15 minutes debugging my code (which was only 4–5 lines). Still, I finally reached CM.
I hate the writer of problem B. Misread B for like 1 hour :(
Before contest, I expected to come back to pupil, but I turned out I'm coming back to newbie
us
We probably find that the difficulties of the problems don't in order such as D1 < C2 and E < D2, it's bad.
will the rating change solely depended on ranking or does it also consider the difficulty of the problem solved?
for example, if someone only solved the last problem and get ridiculous amount of WAs such that the score get reduced to near 0. Their rank fall to the very end, will the fact that they solved a very high rated problem contribute to a rating increase?
I enjoyed the first Div.2 of 2026 (especially E), thank you!
Can we stop getting these brain-wavelength problems like Problem C…
Why do problems like this even exist?
can you guys suggest me some good books to improve english??
My first contest and only solved problem A, and my head already feels like it’s going to burst...
My first contest and i couldn't even solve problem A lmao (disappointment)
Are you going to participate in Round 1076 (Div. 3) ??
I think 2 hours are too less for 8 problems.
Given the writer's frog-like statement, The Curse of the Participant is hands down the better name for Problem B.
The testers forgot to read Problem B. They were busy collecting contributions!
Problem B was more of english comprehension than solving. Also, Problem E should have been placed earlier :(
@Fakewave @yanb0 @furt1ve My submission #359380484 (problem B) got Judging Failed during the contest. It's a system error, not my code issue. I've submitted the same code in practice mode and got AC. Please rejudge it. Thanks!
Can anyone who proved the solution for C explain how they did it?
For C1, you can observe a special case. Since we have freedom to put any number at nth and 1st position. We place 1 at the nth position, since even^1 = even+1 and odd^1 = odd-1. I.e take exor with the nth position number which is 1.
if n is even then by using this technique you will never be able to generate the number n since the second last place will be n-1 which is odd and gives you (n-1)^1=n-2. Hence place n in the 1st position(no constrain).
Similar case for n = odd, you will never be able to generate number n-1. So place it in the 1st position.
359487169
My friend Baskot just got first solve in problem E. I request (on behalf of my friend because he is too shy) from the authors to write the first solvers for the problems. Thank you in advance.
Good round!
forgot to uncomment the xor i was printing to check in c2.............................. imma kms
Is there a way to sort comments in descending order, so I can look at the discussion of the problems.
I swear these permutations and bracket sequence problem will gonna be it for me one day DAMN
D1D2 are definitely one of my favorite problems of all time, and not just because they got me a top 50 rank (and maybe CM if carrot is accurate)
Decent contest. I didn't do well. Only complaint is that it was painful to read A, B, and D.
It was an awful competition, solved the first one in 5 minutes (solved faster, until testing and sending took 5 min), expected to be easy upto the fourth problem, given that first one was so easy. I've read the second question multiple times, couldn't match the second test case, there was also no explanation about how the second test case had that answer, then I moved on and tried to solve the third one, in meanwhile thinking about the third one, I've noticed the update on the second problem, but I was too busy thinking about the third, then noticed I've spent more than an hour for the third and everyone else solved the second problem, I was already at position 8k+ since 8k solved the second, so, I thought it is not worth it, and left the rest of it. I don't know how those guys solved the second problem when the definition was wrong? Did they already know the correct statement?
the statement of B was clear. They just improved it with the update. If it was ambiguous for you, you could check the last sample test.
I got through the problem before the update (but should have solved it much faster).
Ideally one does not need to go fishing through the samples to understand the problem.
And look at D, this was a full sentence? Usually you have some transition to the idea. Instead we then get a sentence after qualifying no ?. Then we get another sentence saying replace ? with 0 or 1. Then we get the actual problem.
"Consider a string s1...sn consisting of characters 0 and 1, and a positive integer c."
when the problem statement is ambigous, one checks the examples. You could probably claim back your time and money from any school you studied math, as they failed to teach how to provide proper definition, here is my answer to previous one:
The problem statement said after each bi, what that means? Does it mean when we reach bi and anything after that? It was definitely unclear, they meant every multiple of bi not after each bi?! (actually how many bi's did we have?) So they tried to make it clear, still they didn't manage formalize it properly but it was understandable.
I was able to solve the problem before the statements were updated, but the original statements did look ambiguous to me, namely the specific meaning of text around "each $$$b_i$$$-th attempt". I first thought it was "for each $$$i$$$, only the $$$b_i$$$-th attempt of jump of type $$$i$$$ requires rollback; all jumps before and after the $$$b_i$$$-th one don't roll back", but rejected that reading after looking at the samples; if my interpretation were true, you would only need at most one rollback, because all jumps after a rollback would be free.
Ideally, the meaning of the problem should be uniquely determined by only reading the statements, without help of samples. In retrospect, the use of word "each" was poor in this problem (it could provoke the reading of "for each $$$i$$$"). It could have been written like "Before making every $$$b_i$$$-th jump of type $$$i$$$, ...", accompanied with a clear definition of "a jump of type $$$i$$$". Also, the original statements use the term "jump" as an uncountable noun, but I think it's normally countable.
The problem statement said after each bi, what that means? Does it mean when we reach bi and anything after that? It was definitely unclear, they meant every multiple of bi not after each bi?! So they made it clear, still they didn't formalize it correctly.
"In the sixth test case, the frog can reach point 10 , for example, as follows: jump 6 times using type 2 and 1 time using type 1 ." 6th case before update:
1 10
2 2 1
even sample tests were WRONG, not ambiguous
worst B problem ever !
Auto comment: topic has been updated by Akulyat (previous revision, new revision, compare).
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http://mirror.codeforces.com/group
http://mirror.codeforces.com/group
I solved the problem 2189C1 independently using a constructive approach based on simple mathematical observations and bitwise XOR properties. The idea is to pair values using i ^ 1, which deterministically satisfies the required condition for all valid indices. Because this construction is fixed and relies on standard XOR behavior, many correct solutions naturally have very similar logic and structure. I did not copy or share code, nor use any public code-sharing platforms. The similarity is unintentional.
I agree with your point of view. My C2 was flagged for matching 63 pieces of code. Apart from the fact that over half of it is identical character by character, I believe a significant portion of the remaining matches are innocent. I hope the authorities can look into this matter.
I'm in a similar situation. This construction is quite straightforward and natural, so I don't think this case was caused by code leakage.
I have just been notified that my solution for problem C2 has been flagged for coinciding with many others. You know, plagiarism checks on such a massive scale are bound to produce some strange results. I guarantee that I did not share my code with anyone. Looking at the people flagged here, about half of them have code that is character-by-character identical, basically copied from submission 359386340. However, while my code and some others share the same logic, we were flagged for plagiarism. My submission is 359402995. I even commented my name on the last line. Additionally, while I was writing it, I included a lot of redundant checks. I used assert statements to force a Runtime Error (RE) in case of issues. For example, submissions 359443883, 359417528, and mine all differ significantly from the code based on 359386340.
If any administrators are reading this, please look into this matter carefully.
Hey ,In this contest i got skipped for it says that i plagarised C1 even thou i did it entirely with my own logic,i looked at the ques and then tried various ways offline and then i got around and got the method that putting 1 and the end and doing xor would do it,it was entirely my own logic but it still plagarised it,so i would like the moderator to look at this condition and see what to do,it say that i plagarised from another guy but the thing is i later solved c2 aswell by tweaking some of the logic while they other guy was not able to do it,so moderator please look at this matter
@MikeMirzayanov
Dear MikeMirzayanov,
Regarding contest 2189 (Codeforces Round 1075 Div. 2), I received this system message for my submission on problem 2189C1:
"Your solution 359388864 for the problem 2189C1 significantly coincides with solutions skiio/359372428, PerkiCrab3104/359385712, SaiharshaASAP/359388864. Such a coincidence is a clear rules violation..."
This caused my entire contest to be marked out-of-competition.
I solved C1 completely independently during the contest. I wrote the code locally in my own editor (no online IDEs, no ideone, no sharing links). No watching streams, no Telegram channels, no groups, no copy-paste from anywhere.
My approach: p[n] = 1, used[1] = 1; for i=2 to n-1 p[i] = i ^ 1 and mark used; then assign the leftover unused value to p[1]. This is one of the most straightforward ways to build a valid permutation satisfying p_i = p_j ^ i — the logic came to me naturally right after reading the problem.
This construction has very few meaningful variations, so many participants end up with nearly identical code (same loops, same ^1 pairing, same used vector). Like several others in this blog are mentioning, high coincidences on C1 seem to be happening to independent solvers due to the problem's limited and natural solution space.
I also solved C2 independently and it got no coincidence flag, which shows my work was original.
I have no pre-contest published source (code written live), but as a regular participant with no previous violations, I kindly ask for manual review as a possible false positive on this constrained problem.
Please admins, look into this issue — many of us are facing the same on C1.
Handle: SaiharshaASAP
Thank you very much.
Best regards,
Sai Harsha
Hello, I’m writing to appeal the plagiarism flag for my solution to 2189C1 (ID: 359413840). My code was flagged with user Mayur778, but I want to highlight that I submitted my solution significantly earlier than they did.The logic for this constructive problem is very straightforward: by fixing the last element as 1, the XOR condition pi = ph xor i simplifies to a basic pi = i xor 1 construction for the other elements. Since this is the Easy Version, it is a very common and logical way to approach the problem, which explains the code similarity.I am a student at IIIT Hyderabad and I have always maintained the integrity of my account. I have never cheated, and the submission timestamps should confirm that I am the original author. I request the coordinators to please review the timing of the two submissions.Thank you for your time and for investigating this.
.