你好,Codeforces!
We are excited to invite you to participate in Codeforces Round 1129 (Div. 2), which will be held on Oct/24/2026 14:05 (Moscow time). Note the unusual start time of the round.
You will be given 2 hours and 15 minutes to solve 6 problems. One of the problems will be divided into 2 subtasks. At least one problem will be interactive so we recommend reading the guide to interactive problems if you have not encountered them before. All the problems were authored and prepared by Getaway_Car and me, _O_v_O_.
We'd like to express our sincere gratitude to:
- Um_nik for preliminary reviewing the round.
- satyam343 for perfectly coordinating the round.
- RockyYue, JDScript0117, AksLolCoding, lkrqwq, nifeshe, szh131421, harmis_yz, Proof_by_QED, employed, ZQZBD, wangzeyu2013, Eterminal, lrb828281, tkdqmx, RainRecall, esc_qwq, MornStar, Libingyue20111, Dim_Star, liang0504, samsoom, a_foolish_OIer for testing the round and giving helpful feedback.
- zhuchenyao, Danielcdo, __WBJ0429__, ztyroy who didn't test, for being willing to test the round.
- Alexdat2000 for translating this round to Russian.
- MikeMirzayanov and KAN for creating the amazing Codeforces and Polygon platforms.
- You for participating in the round.
Good Luck & Have Fun! We hope you enjoy this round!
UPD1: Scoring distribution:
UPD2: Congratulations to the winners (subject to change):
Official:
Unofficial:
First solves:
A: 00:01:49 by ZeeroBug
B: 00:05:03 by Dipanjali_4184
C: 00:10:14 by wangyizhi
D1: 00:21:41 by TasselFlower
D2: 00:27:57 by TasselFlower
E: 00:41:25 by evenvalue
F: 00:27:55 by jiazhichen844








as a writer, i authored
As a writer, Getaway_Car orzzzzz!
As a tester, Getaway_Car orzzzzz!
As a cwOIer, Getaway_Car orzzzzz!
As a contestant, Getaway_Car orzzzzz!
As a newbie, Getaway_Car orzzzzz!
As a (tester),Getaway_Car orzzzzz!
As a AHOIer, Getaway_Car orzzzzz!
As a !tester && !writer && participation, Getaway_Car orzzzzz!
edit: bro????? i did nothing to deserve that downvotes????? if you dont like my comment why dont you move on and leave mine????????
As a tester, Getaway_Car orzzzzz!
As a newbie, Getaway_car orzzzzz!
As a newbie, Getaway_Car orzzzzz!
As a newbie, Getaway_Car orzzzzz!
As a former cwOIer, Getaway_Car orzzzzz!
As a tester, I was red when I test :(
As a tester, I was purple when I test :(
As a tester, god I love interactive
hope everything goes smoothly
Wow cnoi round again
Love the 19:05 start time, hope to see more rounds scheduled at this time :)
Oh but I have to attend ABC on 20:00 $$$Q\omega Q$$$
Good start time for CN participants
其实我也是中国的 但是我"TLE"了"TLE" means time limit enough
yeah
As a tester, I miss interactive xD
Nice round and enjoy
Nice Time!!!
Great time for Vietnamese participants :D although it overlaps with atcoder but I will participate
beautiful handle, beautiful time, beautiful round!
Holy, employed and samsoom in one round, negative 100 points is calling lol
67
as a tester, i dont remember testing
you successfully resisted the temptation to open a single problem
As a Tester, I think this is a great CNOI round!
As a contestant, I hope it'll be a great CSP implementation contest :D
The time is perfect, I like it
As a cucu, caca
Note the unusual start time of the round.
finally, a contest that starts early instead of starting late!
As a participant, my goal is to solve three problems. Good luck to everyone!
Good luck
Good luck!
Hope to reach lgm
Great wish
YESSSSSSS
OvO
спасибо вам за раунд)
As a tester, orz _O_v_O_
How to register?
bro go to contests on top of the main page and register the first red register icon
Go to the nearest registration office in your area
tourist Whoever sees this comment is gay. (except cry , Camal and evanchen )
Ok
Auto comment: topic has been updated by chillingjellyfish (previous revision, new revision, compare).
Bing chilling
zcCN!!! Wish I can solve 4~5 problems and get high rating.
hopefully i'll not begin the contest with chopsticks in my hand
Will Codeforces Round 1129 (Div. 2) be rated for newcomers
yes
hopefully i'll be pupil by this :))
It happened! 1129 div2 will always be special for me :)
As a monkey on a typewriter, pokloopp;p00 scdajtc3w023c23[0c23-c also good luck guys girls others prefer not to says and monkeys ok I'm gonna go write hamlet io3439v3ojkltoer
_O_v_O_ pls make it on usual time bcs your contest overlaps with Atcoder
If we go ahead at the usual time, it will conflict with COCI
that's sad
As a competitor,I am (unrated) when I compete
I love you.
Good luck guys, dont cheat
hi
Perfect start time. My sleep time comes back.
as a tester, i am excited about it sto orz
As a Chinese contestant, it's the most wonderful start time I've seen. Perhaps it's the first rated contest I will participate on Codeforces. Good luck!
may be a up vote
great round
19:05?! not 22:35?! I like the start time! don't have to stay up late
As a Contestant , Getaway_Car & _O_v_O_ orzzz !
As a contestant , i hope that this starting time will help me get green profile name
As a tester,the problems are interesting.
As a participant, lrb828281 dsa dsasa dsasasa
As a participant, Grammar_hbw and lrb828281 dsa dsasa dsasasa
As a participant, lrb828281 dsa dsasa dsasasa
The time is perfect, I like it!
sto zhuchenyao orz
thanks for the song in question A
pro ovo. SUPPORT
So little participants, everyone went to do ABC
The gap between Problem D1 and D2 is too huge :sob
I’ve read them and I agree.
how to solve D2, do we need to find some Pattern in the values of f(n) ??
Here is my code:
The main idea is that a num can be computes as either doing op1 until the highest bit is set and then deleting until you get the correct bits or just adding the bits one by one (you can add bit k, by doing op 1 k times and then doing op 1 again, this will put k and only k as 1) the main idea here is that:
doing it the first way takes m + d (m times op 1, d times op 2) second way is m + f(n — 2^(m-1)), (you can think of this as just putting that bit there and then doing the rest of the bits, which I defined recursively)
if you put these together than deleting is cheaper when d <= f(r),
then effectively we can precompute the amount of numbers for each range of [2^k, 2^(k+1)) that will be cheaper to do in the first way, and that will be cheaper to do in the second way.
then you compute for each for each bit block the total cost.
tbh reading my explanation it makes it way more complex than it really is, I suggest you play around with the bit values of the numbers on paper, the core idea is kinda obvious once you get the hang of it, and the rest is just algebraic bullshitery.
oh and the numbers that are cheaper to delete are all part of a suffix, so you essentially use prefix sums for that, same for low and high, its all prefix sums.
time was cool so were the problems
1/ I lost my brain when solving A
2/ How tf to solve D and E???? TT
3/ So many cheaters....
Hints for E:
B and A shoulve been switched tbh.
D2 is pretty simple at its core (at least for the amount of points you woulve gotten from it), i did a small explenation for aditya. But holy shit the amount of off my one errors drove me nuts lol.
..
The process of checking whether a subsequence is good does not affect the original array
Choose $$$b = [2, 1, 1, 0, 3]$$$
There is already an element 0, therefore, after any operations, there is at least one zero left in $$$b$$$, therefore, the original subsequence is already good.
Deleted
Did you not feel anything like shame while writing this comment? Or does the very 80 IQ that compels you to cheat (I doubt you could even solve 2C on your own) also make it impossible for you to harbour complex human emotions like guilt and shame?
Deleted
why does the reply feels ai generated
If u don't understand basic english what can I do, english is taught as a compulsory subject from school in my country.
Anyways, after getting this much hate i cant think of commenting again. Hoping future days will be better without my comments as i am most hated guy in comments (whenevr i post something got too downvotes :sob)
Still, wish you all the best and hope you crush your next contests!
you are such a misunderstood genius poor you I wonder why you get so many hate comments
you are everything that is wrong with todays codeforces, you want everyone to think you are so smart for solving these when in reality you are just using ai even you comments seem ai writen go kys you ai trash
How to solve D1?I tried either deleting (2^msb) — 1 then recurse on the remaining or get to (2^msb+1) -1 then deleted to the goal and choose the best value, it worked but for larger values it caused overflow any help?
Just a intuitive idea, I think it might be using digit dp, or there might be some observations.
Btw, the problem ask you to modulo 998244353, overflowing shouldn't be a problem
My solution was ok, I just did 1<<n instead of 1LL<<n -_-! I want to jump off the window rn
Bruh back in the day solving a,b quickly would get you to 1500. now im losing 45 rating
"Back in the day" unc :sob:
Good problems
Good contest but tf am I doing, if I could've actually implemented I would've easily gotten AC, please help how not to spend 20 minutes making a simple helper function
My sol is a bit impl heavy but it would be fine if i didn't spend TWENTY MINUTES MAKING A 13 LINE HELPER FUNCTION
I believe I will reach 1200 rating after this round, though I didn't do A and B fast enough...
any idea ? how to improve in contests ?
What to do in D2?
Why did this submission 395859622 get skipped after the contest? I submitted the same code again 3 minutes later 395860335, and both got AC during the contest. The only difference is that I commented out
#define int long longin the second one, since I know it can cause issues with LCA. But only the second one stayed accepted.To my knowledge, if you have two codes with slight change that both results an Accepted verdict, the previous code would be skipped because it is unneccessary to rejudge it in the system testing
Thank you!
Good contest.
What is wrong in this code for Problem B
please read the editorial
Maybe this could help you. input:
1 5 4 5 6 7 8output:
5Why the timings were so odd, i was thinking it is at 20:05 :( ?
150+ solve on D2 but it's hard to find a single legit participant among those...
My solution discussion stream for ABCD1E
So the Dipanjali_4184 is the fastest to solve problem B, after solving problem A all in the span of 5 minutes and proceeds to solve nothing more, while his entire last round got skipped. Yeah looks like a fair participant and deserves to be mentioned in the announcement.
As a first time contestant, and although it is late to say this, orzzz to everyone who helped in this and everyone who participated.
1129 div2 will always be special for me. Finally reached pupil.
This was such a good contest man, really enjoyed it!!
IN Problem B
5
2 1 1 0 3
why answer is 5?
Thanks
the answer always is either zero or n because if you can make one element equal to zero after that you just need to remove every other element so you end up with one zero , and in this case you already have a zero so you can just remove other elements
As a tester, I miss interactive
as a writer, i authored
Hello Codeforces Team,
I am writing to respectfully request a review of the similarity warning regarding my submission 395869936(https://codeforces.me/contest/2277/submission/395869936) for problem 2277F, which was flagged as significantly similar to submission 395853784(https://codeforces.me/contest/2277/submission/395853784).
My Codeforces account, rating, and reputation are important to me. I have been actively participating on Codeforces for approximately 50 days, and my submission history is available for review. As a Pupil-rated contestant, I am working consistently to improve my programming skills.
I respectfully request a manual review of both submissions, particularly the specific matching portions and their implementation details, before any decision affecting my account or rating is made.
I am willing to cooperate fully and provide any genuine information that may help clarify the situation. I would appreciate a fair assessment based on the relevant evidence and circumstances.
Thank you for your time and consideration.
Hello Codeforces Team, I am writing this again,
with sincere respect to request a careful manual review of the similarity warning issued for my submission 395869936(https://codeforces.me/contest/2277/submission/395869936) for problem 2277F, which was flagged as significantly similar to submission 395853784(https://codeforces.me/contest/2277/submission/395853784).
I want to clarify my position and respectfully ask that my submission not be judged solely on the similarity warning without examining the full circumstances. My Codeforces account, rating, and reputation mean a great deal to me, and I take competitive programming and fair participation seriously.
I have been actively participating on Codeforces for approximately 50 days, and my submission history is available for review. I am a Pupil-rated contestant working consistently to improve my programming skills. I understand that account history alone cannot establish what happened in this particular submission, but I hope it can provide useful context.
I respectfully request that the two submissions be examined side by side, including the exact matching code sections, implementation details, and submission timelines. If there is a specific concern beyond the similarity itself, I would appreciate the opportunity to understand it and provide a factual explanation.
I am ready to cooperate fully and provide any genuine records or information that may help clarify the situation. I sincerely request a fair and evidence-based assessment before any decision affecting my account or rating is made.
Thank you for taking the time to review my request.