Maybe this year, Magic is the friends we made along the way. :")

Me and my friend yahya04 submitted the same code twice since we are friends and we decided to do the very last div1+2 contest together , we really apologize since we had no idea about the rules and since it was our fault we apologize and we accept any decision ! sorry codeforces !

As a tester, I want to know why you're not playing Honkai: Star Rail.

As a tester I can confirm that: 1: There are no ‘f’s in c onqueror_of_tourist 2: twosquares is a subset of threesquares 3: I will steal YuukiS ’s profile picture for a week after me reaching red 4: One cannot heal with Auchenai01 Soulpriest on the board.

fhanks for commenting! ill remember you when i go big

I can confirm that for a nonnegative number of minutes during my testing, I was not playing Honkai: Star Rail.

As a tester, I can confirm that: All of the writers are from UIUC UIUC is the best university If you disagree, you will get negative delta from the round

I would like to change my handle to Auchenai , but failed?

Wow, it's Frieren! Now I have to join in! I hope to become a Candidate Master. Wish everyone can get positive delta from the round!

My goat twosquares

Where can i get one of those christmas ornaments?

it is easier to be exposed if i faked lgm or newbie. what about faking gm or pupil :) (whisper: no one will check if i am a real pupil)

Yes it's. https://codeforces.com/blog/entry/100941

orz YuukiS

ok, i'm now an 'international' master. upd: now candidate 'international' master.

Wishing you 12 months of peace and progress.

Thanks, Happy New Year to everyone :) May upcoming year be full of AC for everyone)

I would like to change my handle to Yukino ( https://codeforces.com/profile/Yukino ) but failed to do so for some reason. This person has only made two submission in 2014 on the same day (non-contest, one accepted, other CE) and has never participated in any blog or comments. I believe this satisfies the criteria. Their last visit was 11 years ago.

My first Christmas with Codeforces excited a lot Merry Christmas to everyone

My goal would be to get gold in the nationals this year, and go on to get a medal(any to be honest) in EJOI, and become Expert again on the way.

Bitwise or nah(I read both blogs)? Just realizing we had the same idea on handle color

In fact there is another 'r' upside down in 'b', so for a total of 4 'r's.

Of course, the same as the regular contests on Codeforces.

It would be wonderful) It would be great if rules about inactive users also change especially the one about Accepted submission in less than or equal to 2 contests

like we would always be getting an non decreasing array even after the first mad operation, so we can devise a formula from there and get the answer like i have done in the submission ( 355125607 ). but i still dont understand whats the need of second mad operation. moreover even after following the rules on the second mad array its quite possible that any number might appear only single time like for example the last element

Time passes so fast .... finally year came to an end

You're welcome. And would you mind me ask another question? Why the complexity of problem G is $$$O(q\log q)$$$, not $$$O(q)$$$ or $$$O(q\log V)$$$(you can regard $$$V$$$ as $$$10^9+7$$$, for the complexity of quick power)? Thanks.

You are only allowed to make at most 3·n² + 150 queries, whereas the current implementation makes 4·n² + n queries, which exceeds the allowed limit.

This magic is so interesting!haha Happy new year,every one!

If u fake a rank lower than ur true one,I will look at ur comments and expose u right under.

hyw.I have already start the game seriously.

Ever seen an IGM with a rating equal to mine? :)

It's not last :D , There's Educational Codeforces Round 186 (Rated for Div. 2)

Oh sry I am Chinese and I'm not good at English grammar, so I copy this sentence from others, but I forget to change the '-' to '+', now I change it, sorry for everyone see it!

CAUTION: 123hope is a legendary grandmaster under the disguise of newbie level.

[image]

your rating seems like the number shows on the problem, by submitting 9 failed submissions and a succeeded submission on it during a contest and get hacked after the contest. upd: how did i save 4 times in 10s??????

How can someone achieve that rating (shocking cat emoji).

Sadly, anti cheating will never be strong enough cause AI is advancing very fast.

Also, this persistent treap has many limitations in some problems. (For example, in Another Problem of Persistent Balanced Tree , you won’t have a good experience if you use the treap we discussed.) Therefore, I also suggest that you learn FHQ-Treap to solve problems involving segment updates.

DO NOT learn CP in China. You know, Codeforces #1 got rank 41 in China NOI. This is really terrible.

In fact, just like what zxx said, "Chinese OI is a competition which gives you a random score". Luck really counts in China, at least for many of seniors I know who got silver or gold in NOI, because they admitted that in person.

Insha'Allah, Would be my best open-source contribution yet!

Hope to get a positive delta in this round!!

Have you seen XOR Linked Tree ? I think your blog's idea is the same as from XOR ordering to DFS order in the Discussion (Advanced) section of the above blog The technique can be expanded to support lca, euler tour, hld, small to large, ... and yields the fastest runtime on all problems in the tree section of cses.fi

I Hope dark mode is introduced, it is the one of the most needed thing for this website..

Never seen this before. Thanks for the link

u can change ur handle once a year, I mean every year u can change....

you can change your handle only once per year . that means that you can change it again next year .

@Dominater069 is this a solo like IOI or a team event like ICPC?

Is there any way for working professional to also participate

The best part of this post is that you mentioned its anti-cheat! Jokes aside, great work!

According to my own experience, you can download offline ide for c++, that will be much more convenient to solve the contest

What the hell is going on in codeforces. Has it come to this that we cannot even understand a joke and get offended by it and connect it to our religion. give me a break!! This user should get banned.

I disagree !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Switch to the Russian version, it does not require to confirm Santa Claus is real

[image]

Div1C2 editorial mentions "the number of pairs of non-concentric substrings with a total length of $$$s$$$", but doesn't describe the way to find this number. Seems not obvious to me. Tried googling and stuff. No convolutions are required for this, right?

[image]

Wanna end this worst year with this good contest :) HOPEFULLY!(

Allah sefa versin IOI-da jim vurarsan unudarsan

Be a speacialist first.Solve problems around your rating is nice.

Johns Hopkins University (received a promotion email a few days ago): Ste , cheollie , Mishazher

I couldn't agree more. As the Chinese saying goes, "As virtue rises one foot, vice rises ten.(道高一尺，魔高一丈)" This reflects how the fight against cheating is a perpetual cat-and-mouse game: however fast anti-cheat technology advances, ways to bypass it keep pace, leaving the best protections vulnerable.

Advancement Unlocked: TIME TRAVEL

how do you have a IGM name on 1300+ rating??

When I code on my phone, I use an app called Coding C++. It's quite comfortable.

Hi MikeMirzayanov ! Thanks for implementing this feature. I'm have a third-party application that uses the Codeforces API and OAuth to track user profiles. I noticed that querying user.info with an old handle returns the new handle, which is very helpful for syncing handle changes automatically. Quick question: Is this redirect behavior permanent, or is there a time limit after which the old handle stops redirecting to the new one? For example, if someone changes their handle from oldHand

It's nice, yes, but Dark Reader makes codeforces weird and unreadable now, and without it Codeforces is too bright/white(for me) :(

He got disabled! I'm not sure if it helps, but might as well tell ya

I am a beginner ...should i register in this contest ?? Are there any easy questions??

The tasks are very interesting and creative. Good luck to all contest participants.

here is my solution for D which can easily be extended to Bonus of D as well. 355263118 Feel Free to ask if any further clarification needed. (I modelled as decreasing subsequence dp)

Finally, everything is back in place, and the universe is safe. You almost created a destructive paradox

so basically you can change your handle what you want but if you want to take someone's else name, you need to participate at least 10 contest, i couldnt delete my account so my name will be random.

Especially around Christmas time, when Dark Reader makes Codeforces unreadable because of snowflakes

There is a hack

How to solve the problem H — Prefix Game? I came up with a logic, but it gives a wrong answer. Can anyone help me correct it? I am mainly focusing on the "gap" condition, where v[i] — v[i+1] > 1, or v[i] == v[i-1]. I treat such cases as gaps, and according to my observation, the player who encounters the first gap wins the game. Can someone explain why this logic fails or how it can be corrected?

Can you share your solution Link if possible?

Do you answer questions about the problems you have solved? I downloaded your submissions, I'm just curious where I'll end up stuck.

Editorial

Cool! Specialist got gold medal! (A late Merry Christmas :)

Happy New Year! The last Atcoder Beginner Contest in this Year! Hope Perfect Ending! :)

Due to technical reasons, Atcoder is unable to host any more ABC events this year . Please cherish this final ABC event(:

I hope that I can solve 5 problems and get MORE and MORE ratings!

G is cool. I see number theory problems like that I press upvote.

Again this year, if you've participated in at least 10 rounds At least 10 contests

[image]

Wherefore must we make haste to garner wisdom, for Time, that swift-footed traveler, doth leave us in his wake. The world’s dominion shall belong to those who, having sought a paradise of dreams and found it not, did straightway fashion it with their own hands.

waiting from 15 min.... still my status is in queue for B and C

__baozii__ comes again!!

I have another DP approach where the problem can be reduced to a standard maximum-sum grid DP. Consider the three arrays as a 3×N matrix. Notice that from (r,c), the only allowed moves are (r,c+1) and (r+1,c+1) We can compute this easily , since there is only 3 rows and N col. in o(N)

my solution using binary search on concave function cpp: PROBLEM B SOLUTION

I view the friend submissions, no one (it caches) Friend A solves the problem I fetch the submissions, still empty (because for the old cache) Fix this issue!

"Good Bye Rating" ahh contest, for me, couldn't solve D :(. Either way, nice contest!

ok So there are indeed two 'f's in conqueror_of_fourist

Please stop chaotic verdict message, I was so bothered during the contest... But short logos of verdict (like [WA2]) is good, please keep it after the new year's chaos.

I have been thinking about randomization in E for over an hour,but the solution is correct in any case.The solution was amazing but perhaps the disablement of hacks and the non-adaption of the interactive problem is more likely to make participants not think about that.

anyone pls help me implement the m = 0 case for D. My logic that I thought during contest was something like storing the elfs in multiset and then attacking largest and second largest and thus second largest dies and largest hurts. So, i remove(both) and insert(the health after hurting) in multiset. Any help will be appreciated code : full code : 355403171

It turns out that for each of the children in this range, we can choose each of their signs independently bro this took me so long to identify this in problem C

Please check out this YouTube video; it was streaming problem solutions live: Video Please ban this cheater Ananya_CodeNova who was streaming those solutions. Also, please review submissions from this account for cheating detection of other users.

sus comments javabidov please take a look at his comment block on top YuukiS twosquares his submission 355400798

It asks for ded moroz and he's a different fictional character

How to solve E? I get WA on test 3, when I use binary search for it. I compared sum of l to m divide m+1-l and sum from m to r divide r-m.

I also used dp you can check my solution. 355361808

Great contest with good quality problems. First time solved 6 problems in div1 + div2 round, a perfect goodbye.

Guys, there are 2 C# submissions that won't judge

Why do the judging system stuck with these two C# submissions?

Why throw away the value you already computed for the sums? the difference is just the value (or absolute value) of a[i]. Also the first element in the array can never be taken negative because it can never reach the second position.

355419853 355419912 I think you should ping some admin for rejudge.

Ok , There you go K AN , Error_Yuan

After rating change, my color reverted to normal :< Did this happen to anyone else?

You should test it with codeforces's "Custom Invocation", which will be more consistent with the actual situation of the online judge.

This is probably the best round I've ever participated in. I enjoyed solving the problems, especially upsolving G.

mayank69goel got banned!! He was Rank 11 in India !!!

so yeah like i thought c was pretty hard anyways e was kinda interesting to look at but i couldnt solve it

Even though I didn't solve the problem nor read the editorial, the last two elves ( m=0 case) does not need to be same health, for example: h[i] = 10, h[j] = 15 a[i] = 20 (because other elves attacked this elf before), h[j] = 15 Then both elves would die at the same operation

I am using a multiset here because i'll insert the remaining health of the suriving elf in the multiset after removing both the elf (the attacker and the elf being attacked in my case they are 2nd max and maximum of the multiset). So, it can be possible that the suriving elf have a health equal to some existing one. For example : 1 ... 3 4 5 8 then 5 attack 8 (or 8 attack 5) : 5 dies and 8 surivied. So, i'll remove 5, 8 form my multiset and add (8-5) in the mutliset. But there was a 3 a

Oh yeah ig I forget to do that thanks! But wait this code even fails on test 1 : 6 0 998244353 1000000000 314159265 676767677 999999999 987654321 It gives something like : 5 5 2 6 1 3 4 1 4 2 4 So, i mean this should not be the case for 1 elf to remain. Every one must die. So, it mean there might be either bug in implementation or my approach is wrong. If 2nd is the case then i wanna know why. Atleast i want to hear it form someone else except me :)

UPD: I got to know that this approach is not correct. I dry run this thing and yes i got it. Thanks

This happened before AI too, tourist does fail to solve some easy problems sometimes (not saying AI did not have involvement here) For example, CodeTON Round 4 (Div. 1 + Div. 2, Rated, Prizes!) had 700 official solves on E which tourist did not solve

Competitive programming is meant to be fun. The time spent digging into these issues could have been better used on your own problem-solving. Calling out people like this feels like a waste of effort.

That Makes me wonder , since the rejudge happened after the rating calculation , will the updated rating for StarSilk apply in the next rollback 💀 (moved from Rank $$$7$$$ to Rank $$$6$$$)

Glad to be a part of this. Hoping that everyone enjoys the event.

why not rating change instant while changing the rank? Spoiler

Hi , The admins will look into it. Sorry for Inconvenience

How are you so sure about this? He’s an ICPC regionalist and part of one of IIT Delhi’s top teams as well.

Everything is back now ! You can register !

I thought I've trained hard by the end of 2025,but last night I was stuck by D and haven't noticed "removing maximal" in problem E so I got -77. It really makes me depressed but I think I will get a better score in 2026.

I am not supporting him, but I am asking for proof. Give us some proof?

if he is a cheater he should be banned, I am myself from IIT Kanpur and I have seen so many people cheat here because they want to get internships, its honestly sickening. These morons are destroying the culture of cp in general. Gosh I hope we can go back to pre AI times!

You can check this DP implentation. My states are (idx,zero) -> zero is used to track whether zero is used till now. 355361808

When I first saw this problem, I felt that this problem is somewhat similar to 1068 B. Niko's Tactical Cards in which DP was used , as I haven't studied DP I was unable to solve it . I just did a simple way by having two variables ( minAns and maxAns ), submission In Goodbye 2025 C, I used a different approach, which is brute forcing the child not picked in all operations, by precomputing the left and right answer, submission Also, I found the WA case a=[-2, 1, -3, 5] , yo

As soon as I read the problem, my first reaction was prefix and suffix sums.

Super excited to be a part of this, would highly recommend everyone to participate

He is from TLE Eliminators. They deleted all his PCD's.

I had the same feeling with it being similar to problem B,but fastly realized that there I need a different approach.

i mean i have been looking into him for some time now, ever since edu roun 185,and even before that. recently i talked to someone who wrote a blog about him and then later deleted it becuase they had the wrong info(confused c2 with D),and i had proposed a joint discussion discussion for a blog to gather proof and expose him even they after sometime said that they didnt think so, and due to the skipped contests i also thought he was still cheating. but after actually looking into his code, th

Merry Christmas and a Happy New Year (。・∀・)ノ

Please everyone report this telegram channel too, it posts codeforces solution during the contest !! https://web.telegram.org/k/#@codenovadiscussion

imo, problem E could have been really hard if a guess was not possible from the max number of queries allowed and typical sum setup which demands for B.S. in interactive problems.

He has many skipped contests. You can check here https://cfcheatdetector.netlify.app/

How could you solve 1600 rating problems but not a single one in Goodbye 2025 contest?

Yeah, in Codeforces cheater database ( https://cf-cheater-database.vercel.app/ ) from an official admin of Codeforces (repo here: https://github.com/macaquedev/cf-cheater-highlighter ) has his username. He cheated once

Link for the code for first problem Distinct Values Sum isn't working cry can you please fix it ? btw i like the idea for problem <3

https://cses.fi/paste/2d15c9c12179f830d3d8d7/

lethan3 OFZ

Unfortunately, we have very strong evidence showing that he was cheating yesterday. :(

Here is a link to a decent chrome extension with in-built dark mode for codeforces. Chrome webstore link

You should visit this website here two types of contest are held one contest is where only the answer is required for question which happens weekly mostly targetting a younger audience and biweeky (after every two weeks) a solid proof based contest is held which is graded live by the creators of the web here is the link

Curious, but are you also using Rust? I am also experiencing this error while submitting for Problem E, and was wondering what was happening since it compiles fine on my IDE.

Interesting, likely an issue with the site. I wonder if the round will be unrated or not due to this issue.

Quick take This is wonderful — a tiny, funny, painfully honest allegory about lust, obsession, and academic hubris. It reads like a dark romantic comedy in six paragraphs: charmingly absurd, nicely paced, and emotionally sharp. What’s happening (brief) It tells a first-person story where the narrator abandons a real romantic relationship for a mysteriously personified ideal called the Tree . The narrator’s devotion flips into monomania (studying), then into humiliation (failure on the T

I do not believe so. I just submitted to E, and my code is stuck in processing and shows 0/11 passed despite showing it passed the first case in the editor.

code In Problem D why it is Accepted i thought i will get TLE

ppl be posting ANYTHING just to farm some contribution

No, actually I took my time to review this semi-understandable blog that has been posted in obscure competitive programming forum and purposefully copied gpt's writing style just for no apparent reason. No shit, Sherlock.

can u provide the apk file for the app please

There is a discrepancy in the problem statement vs. what is accepted for problem D in this round. On the problem description, it states 3 0 31 is Expected for the input of Test cases 1-3. However, in the Repovive compiler, it states that 3 0 81 is expected for the initial test cases. Could you fix this + Rejudge?

You're binary searching for the half with the bigger sum, but the half with the bigger sum doesn't have to contain the maximum of the array (e.g. 2 2 2 2 1 1 1 1 4)

This magic stuff had me doubting if a gm was really asking this.

Obscure is a pretty strange word for a site that held a contest for 30k people two days ago.

Unfortunately, nothing like CF exists in math because rating mathematical proofs is quite difficult, since unlike code, math proofs are not always built in some unified formal language. If you just want to improve your number theory skills it seems that solving past school olympiads like BMO/IZhO/RMM etc or books like "NUMBER THEORY Structures, Examples, and Problems" by Titu Andreescu is better, Well it is better if you look for smth similar to cp problems, if you looking for some

In this blog [Tutorial] A way to Practice Competitive Programmig by E869120 writed: Sometimes, especially in Div1+Div2 round, some problems need mathematical concepts or thinking. Since there are a lot of problems which uses them (and also light-implementation!) in TopCoder, you should solve TopCoder problems. So maybe TopCoder Div1Easy good place to improve math. (I haven't tried it yet)

Btw also try IMO and other olympiads' shortlists

You clearly didn't use AI to write this shit, I can give you that.

> "For each participant, we will take their latest submission with a non-zero score (as of the contest end) and re-test it on this hidden test set." But what if the latest submission got a lower score than previous submission? It's impossible to resubmit the same code. Is this a typo and is this supposed to be "latest submission with highest score"?

so many cheaters in last round, it's last contest of the year, I hope we don't see another round where 10000 people solve problem C.

If you're asking how I constructed the counterexample array start with 8 as the starting number you can flatten the arrays into 4 4 then 2 2 2 2 and for the second into 4 4 then 2 2 4 then 1 1 1 1 4 and concatenate them. If you're asking about the solution, you can check the official solution in the editorial, it's quite interesting!

try -Ofast , it looks like they compile without -O2

you can find problems of contests on this link : https://repovive.com/problems also now you can enter in any past contest :)

nvm this is heuristics problem, latest submission makes sense

240 E Road Repairs the sloution sould be directed MST but simple bfs works and you could easily make a test case that would give wrong answer on most of the accepted solutions out there(the output graph is not connected)

Div4s problems are so generic and mundane it should be discontinued (And, two years ago I had the same question as yours, but I realized how bad Div4 has become)

You see, I totally forgot about that part, lol! Sorry!

Can't wait to get cooked by Dominater069 problems :')

Wait so it's mostly interactive? Oh no... ;-; I'm good at graphs, trees and not bad at seg tree but very bad at interactive, and graders

It wasn't just because of cheaters, the problem was probably the level of Div2 B.

There's an $$$O(n)$$$ time for 2178D — Xmas or Hysteria . Idea is almost same as editorial, except that we now need a strategy $$$S$$$ that runs in linear time and does the following : On input any sequence of elves $$$Elves[i,...,j]$$$, output a sequence of valid attacks such that at the end there's exactly one or zero elf remains. Now suppose we have such magic $$$S$$$, then for $$$m \ge 1$$$ case : same as editorial, except that we're gonna use std::nth_element to put the largest

Bro didn't get his fair share of negative contri...

It was a dp problem and I have seen myself that AI can explain and solve DP very easily that's why I am saying there were a lot of cheaters, even a master level cheater was caught buddy in the contest.

Try Project Euler

2174F - Mosaic Tree Some hacks for this problem still result in Unexpected verdict (1160229 to 1160235)

I solved it using a dp approach — https://codeforces.com/contest/2178/submission/355396319 and like I said if a problem can be solved using dp then AI easily cracks it because essentially it becomes an optimization problem which is fundamentally how machine learning and AI models work.

I think this solution: 355700213 for problem 2138C1 - Maple and Tree Beauty (Easy Version) can be hacked. It only checks for sum k (or n — k) and ignores other valid distributions.

4k on D, in 2 HOURS, is unreal... I barely passed first test

For Macs, just download GCC from home-brew, that is how it worked for me and change your compiler to gcc in your preferred IDE, it may still show error for bits/stdc++.h and ordered set libraries when importing but the code will compile for you, to fix the linter you will have to go through a lot of trouble which I dont believe is necessary.

You will be needing a GCC Compiler (you can use MinGW or something)

there is literally an entire paper published by Deepmind (the first pioneers in Reinforcement learning algorithms) which basically tries to prove that Graph Neural Networks are basically dynamic programmers. Here is the source — https://arxiv.org/pdf/2203.15544 I am myself working on RLHF at the moment and I can argue that dp is involved everywhere in RL due to policy optimization, monte carlo methods, etc. These types of methods are used in AI technologies as RLHF (Reinforcement learni

I used a greedy approach with priotity queue by first matching boxes to eligible friends who have the highest cost, and then spending the remaining cash on the lowest cost friends left which maximizes the count. Submission (Rust 2024): https://codeforces.com/contest/2182/submission/355740776

Why makes a permutation unsuitable? Given that there is a valid permutation(answer > 0), what differentiates permutations? Once you figure this out, the rest becomes intuitive.

All RL algos are Bellman equation, which is used to solve dp, so it's not entirely true to say dp is used everywhere in AI. Also RLHF in practice barely uses pure DP, but rather approximate DP like value iteration. I think you meant "DP principle" instead of "DP". Anyways, "dp is better for AI" doesnt inherently mean "AI can easily solve dp problem".

For i = 0, you can calculate all valid j(ignoring k for now) in O(n^2). The number of valid j can be called val_j . Note that if i = 1, each valid j is also incremented by one. Therefore, the total number of valid (i,j) pairs is n*val_j since i can be any value and there will always be the same number of valid j. Next, we can repeat this logic with j and k. For a given j, the number of valid k is val_k and can be calculated in O(n^2). The number of total valid j is the number of

4000 AC on problem D? CP nowadays is becoming a nightmare for legit contestants

I also tried and failed, but I think my general idea was close. Think of it like digit dp with dp[pos][tight][started]. DP is not necessary, but the ideas are useful. Considering started as an implementation detail, and pos as each bit, you can iterate downwards through the bits. Let's also define t as the number of bits greater than our pos which are in the x . Let us also assume tight is always true. If the previous bit present in x is p , we can do some casework. If we s

A quick (scientific) note to the authors pertaining to F1/F2: The carrying capacity of a population (a group of a species) is the amount of organisms that can be sustained in the environment. It was pretty clear towards the end you were referring to carrying gifts, but just a FYI.

Yeah sure, I just wanted to give the idea that dp is involved in optimization and RL algorithms. The whole point of the previous source is that the general dp related problems are easier for AI because of their own architecture resembling an optimization compared to other types of problems. This increases the chances for cheaters to get correct results compared to other types of problems.

hoping that it does not goes unrated as I performed good and it was my first contest.

5 5 1 2 1 2 3 1 3 4 1 4 5 1 5 2 0 Expected Verdict: Wrong Answer submission: 353101962 this is my test case the most codes give WA on this (in the answer graph the capital is not connected to any other city) for example my AC submission gives wrong answer on this

There is a 12 hour open-hack portion, I believe after hacks end (11:35 PM EST), then the editorial will be posted.

Emra umarim 12 senede ingilizde ogrenmissindir

For International participants in the online pre-lims, will there be a file upload option for screen recording on the site, or would we share the file through a platform like Dropbox?

I personally think dynamic programming approaches are more intuitive due to the step-by-step structure of the dynamic programming. Similar to proofs using induction, the idea of computing the answer for $$$n - 1$$$ steps and understanding the relationship between consecutive steps, hence being able to compute the next step makes a lot of sense. I think in general it is just more intuitive to more people. If you understand what you need to compute, then the relationship and transition between

Nice! I took so much time on B that I only had 30 minutes for C so i just didnt try.

+1, re-read the problem statement multiple times to make sure I wasn't missing anything.

holy shee, her using rust for cp was off putting ngl, I donno bro sometimes i feel like cp is approaching to be dying craft with the advancement of llms

well the contests havent been reduced yet right....theres hope

Curious, but what is wrong with using rust for cp?

lemme redirect to a stack exchange sire, it shall explain it astronomically better than i can from experienced rs devs pls check this

Pupils literally solved till F within 15 min.

your physics teacher would uniractualowkirkenuinely slime the shit out of you

can you report them on youtube (assuming anything is even done from that) or can they only be banned on codeforces? this is actually worrying also are these submissions exactly the same because then they would be easy to catch

magic will include ranks such as headquarters, unrated, tourist/jiangly when?

most definitely hackable if N^3 due to no bounds over all tc 1e5*(1e2)^3 = 1e11 TLE heres my O(n) sol instead note that only the last occourance of the largest element matters, lets start by reverse sorting it, for each element after it, it will go max-it-1, -1 because its after it so we can stop after making the max 0 if we move it before its max-it, so its +1 for each we move before let x = arr_0 as long as this sum <= x, were fine, so we know what positions the last, now in a for

I doubt any of those except possibly unrated would be added, simply because headquarters would introduce far more scams for impersonators, and tourist/jiangly ranks (4,000+) are based on your own handle, which would require Codeforces to put your own handle as your rank which could be done with API calls but likely won´t due to the sheer rarity of the title or resource limitations from thousands or more users calling the API to change their title.

I believe it will, but we should wait for the official contest announcement before we make any assumptions.

I want to report cheater wegokic234 with using LLM Here https://codeforces.com/contest/2182/submission/355745999 And you can see this code has if (!(cin >> ... ))

chreh OFZ

thanks dude. NOT going for IGM tag, expert is good enough for me :)

GG I think that was a great year for everyone , best wishes in future year :)))

I am still learning dp, but the first thing that came to my mind was to use prefix and suffix sums on that problem.

BledDest The problem B is missing a test case. Input: 1 5 1 2 3 4 5 1 2 3 4 5 Output: 1 5 The solution provided here causes undefined behavior and buffer overflow for this testcase. I think the test case should be added as I have seen some submissions giving wrong answer for this case.

Isn't it an invalid scenario? You cannot get a' from a for any l and r

i think 2100rating is very enough.（If I wasn't particularly tired during the competition, I feel like I could AK this round too)

The ranklist is completely blank right now.

What is the purpose of cheating on codeforces?, is it seen in some professional setting?

How can one come up with ideas for ad-hoc problems like problem H? Are there other problems that use the same idea? I honestly think I would never have been able to come up with this on my own.

It was combinatorics... I solved it in my first codeforces contest because I also do olympiad math, also I have given atcoder contest.

Hopping that codeforces finds a way to ban all cheaters because it isn't fair. some peoples try hard to perform better and hoping for +rating but these cheater sol problems by cheating and get good rank and we just....

I'm kind of new here, but I heard from others that 40 contests is not a lot. In general, try to figure out why you couldn't solve the problems you couldn't solve. Did you run out of time, is there a math/logic insight you didn't get, is there a certain data structure or algorithm you didn't learn, or did you mess up the implementation? Do more specialize practice on where you find challenging, and you should see improvements. Regarding accounts where they became master or specialist in ju

He solved till E in just 20 mins. Were Questions leaked?

Yes, if the number of digits shifted to the left exceeds or equals the number of digits of the data type, the result is undefined .

Thank you for taking the time to share your experience and insights. Your explanation really helped me see the bigger picture of how to approach DP problems, especially the balance between greedy thinking, core DP patterns, and optimization. I really appreciate it.

HOPE CODEFORCES DO CodeChef LIKE THING IN EVERY CONTEST.

The rating depends on where you are in the competition. you often solved 0 tasks or 1, while others do more, there are people who do it through AI, as a result, your place in the competition is lower and the rating drops because of this, try to at least occupy the top 5000 places, at least 6000 And it also depends on the number of competitions you've participated in.

It took me a year to get to Pupil, my recommendation is to practice on problems that you wouldn't be able to solve normally. e.g D div 3s, etc. Also train on different websites too, the training I've gotten helps me a lot.

I have checked his submission and I believe that all of this code was written using chatgpt. I can only be grateful that I have solved more problems than chatgpt.

Guys can I share solution on Youtube after the contest?

Look at this profile: Little_Sheep_Yawn

Rating updates for the round have not been done yet.

Hello everyone. Have a nice day. Where is our ratings??

Watch mamikonm1 streak. orz mamikonm1

Northern Eurasia, Kazakhstan, Nazarbayev University, clearly straight guys: seduneon , kenzhik , fractal

Yes, many others share their approach after contest, just never during contest.

Dang, 9th grade? Massive congratulations to you and WBJ0429 ! ^-^

Just wait until MOSS detects them, they´ll be banned eventually and rollbacks will happen.

Ratings were recently published. (Congrats on CM)

Try to solve problems slightly above your comfort zone. maybe 1200-1400 for you(figure out yourself). And after questions feeling simple try to move towards harder questions. And if you come across something you don't know, take some time to learn it. Also don't take rating too seriously, as cheating has affected them a lot.

$$$t <= 5e3$$$ and $$$n <= 50$$$ though.

Thanks. Congrats to you on ranking 1st lol.

This is infuriating bro! Solved ABC in 40m and it seemed like not even enough to reach pupil

https://codeforces.com/blog/entry/18051 heya ya go u can read it from here for now :D source is source o_O but teaching might be diff :p

why yall down voting.... do you guys will like if i down vote yours? im just saying happy new year.....

The link shows your are not allowed to view the contest . Is there any glitch which will be resolved before the contest or any problem with my account?

Reminder: Only 10 minutes remaining GLHF!!

welp life could become sometimes mean... well who damn down voted me know that i dont pressure on you;/ maybe yall angry or something to have reason to down vote.... if u down voted for fun uhh still merry x mas :( if u down vote pls say why atleast...

other blog posts were saying there was a lot of cheating not using ai

It says SSL Handshake failed when I try to open the website, Any solution?

so they all become *** **** and down vote? like they could just pretend to not see why there are being so damn rude like i had -10 contrib now it's -24 like f this s up bruh atleast i wanted make it 0 not extra -14...... but atleast ty for saying the truth....

Congrats on the start of your journey, I also got rated as a Newbie with 997!

Read the editorial in the announcement https://codeforces.com/blog/entry/149733

Idk if you are lying or not but yeah old code can get submitted if you have not saved your file in case. So, yeah it's pretty possible

Also a kind reminder for everyone, kindly do not tag mike or anyother headquater members, if they fell the needful they will be informed by internal channels and other community memebrs they have a raport with. there are 100's of posts like these and i am not wishful enough to think that i or the Clanker have written anything that is just extraordinary. Mike if you are reading this happy new year to you and thank you for codeforces.

Before, you could become a pupil by solving A and B, but now there are too many cheaters. Now you need to solve A, B, and C , I don’t support cheaters , I hope in 2026 cheaters will be less than 2025 , welcome 2026

I have mentioned that this post was generated with my help and the Clanker did all the actual heavy lifting

Actually, by “this topic” in the last part, I was referring to my own meme’s topic. So yes! lol

Breaking news: local cheater makes a blog about cheating 345618961

I have mebntioned this earlier and i will reitterate it, the submission i had made were in hopes that my friend who cheats will get skipped that contest as i had access to his chatgpt, however he had integrated the code into his template and did not get skipped. this is not my main account nor is it a reflection on my performance, in retrospect this was a very ill informed descision as i did not achieve my goal and at the same time i disrupted actual contest performance of users and for this

two reasons, writing a blog initself i do not interfer with anyone elses performance or cause anyone any harm the clanker is the llm, cheating using ai causes harm to the community and other people for your own gain, if ai can help me in certain tasks that i do not have a particular skillset for and make my words more cohhesive i surely intend on doing so and such is my right, for i am not affecting anyone else by leverging on an llm for writing and formating a blog. your argument creates

this right here will probably go down as one of the best arguments to come out in this millenia

wow, a blog written by newbie has positive upvotes. I guess it really is 'MAGIC'

i don't think you needed the "magic" button to show us that you're an international master man. congrats on rank 1 by the way :)

Manifesting Expert ! Happyy New Year <3

"two people who see the world for what it truly is are a poor man and an unattractive woman"

Am I like the only person who could solve D but not C?

[image]

The .size() function returns a size_t type, which can be considered an unsigned long long when the testing machine is 64-bit.

Respectfully, I disagree to some extent. There is some ratism, but not nearly enough to account for all of the correlation between rating and votes. If we're talking about shitposts, you're partially right. An LGM like Um_nik can post whatever they want and probably get a few hundred upvotes. But also I've seen some shitposts by lower-rated members get a decent amount of upvotes; I mean, this one has +391, for example. Anyways, a lot of shitposts by grays are just stupid and not v

I'm pretty sure it means Permutations and Combinations, since P and C are the shorthand for those two respectively (i.e. nPk/nPr and nCk/nCr).

oh prolly !! would be better just copying from IDE

i would like to try something like this. Looks pretty nice and amazing!

same, i upsolved D without looking at solution but cant understand C even after looking solution of it

"How did that specialist get 2nd? I think he cheat. Please ban"

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I guess it takes a snapshot when calculating the color change, you are blue (because of magic) when the rating change takes place and becomes pupil (green), so the system thinks that the color is different and display that How does this thing disappear after new year is a complete mystery tho

My guy Aritro_ put it in quotation marks and you still thought he meant it...

It's pretty cool to see that rank $$$x$$$ gets $$$\lfloor \frac{1000}{\sqrt x} \rfloor - (x - 1)$$$ points in each contest(only for the top 100 though).

Life is two days, one day to your detriment and one day to your detriment.

hayagrivan.dj Issue: CompetitiveCompanion — Atcoder Parser kept failing because of installing AC Analytics. Could you please edit manifest of this extension to not work on Problem Page? Or like make it compatible with CompetiveCompanion Extension.? Could you please opensource it? — It would make it easier to maintain and fix issues for me.

I found a workaround. Find Install path of extension using Extension ID Windows : C:\\Users\\[YourUsername]\\AppData\\Local\\Google\\Chrome\\User Data\\Default\\Extensions\\{ExtensionID} Linux : ~/.config/google-chrome/Default/Extensions/{ExtensionID} For me : Extension ID is fbliobpicoanacbncphlgaghdkodkgme (Source: chrome://extensions/ ) Edit Manifest.json — It's better to copy extension folder to another folder and then

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I feel with POTD it should be random and not based on Topics

Editorial

hey everyone, just started doing codeforces again, anyone have any idea how many ques i need to do in div 2 to reach pupil and any tips to reach fast?

i think you are missing that you use java (runs slow), i recommend using c++

i tested it out on chrome seems to be you can connect with me on https://www.linkedin.com/in/hermitparth/ i can help you there properly

I was about to upvote until I saw the AI-like writing style and the em dashes.

have reloaded 100 times still my comment haven't came :(

Can anyone explain to me what are GP modes.

Bro I saw this comment today, I think it was by drydock .

lol , I got my comment from the first try 💀 💀 [image] [image] Reference

As an problemsetter of the previous version I highly recommend participating. Last year’s finals was awesome and I can see this one being even better

Hard [image]

Suppose we are querying the whole array. For the case where $$$k = 3$$$ and $$$a = [1, 2, 2]$$$: Among all four subsets (of values $$${1,2}$$$), two are bad ($$$p_{bad} = \frac{2}{4}$$$). So we see $$$p_{bad}=\frac{1}{2} \neq \frac{1}{k}=\frac{1}{3}$$$ Also if we have an array with counts of elements $$$\in {5, 10}$$$ and $$$k = 10$$$, then probabilities are the same as for $$$k = 2$$$ and counts $$$\in {1, 2}$$$.

when this comment is shown in the game, plz choose master/intermaster cuz i'm not :)

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Just write good shitpost duh, nothing to do with rating. Obviously, my shitposts wouldn't get many upvotes if I were not LGM, because a lot of people wouldn't even open the blog. But I don't think I would be downvoted either. LGM gives me more visibility, but the blog still needs to be good to get upvotes, and if it is bad, it will be downvoted.

At first glance, problem E looked REALLY similar to an old problem from COCI. I'm not sure from which contest but it was here: https://evaluator.hsin.hr/

You touched most of us like me.. thanks for spreading this info :) btw HAPPY NEW YEAR

uhh what i can say but the blog u gave an example is like a bit tuff like what could bros do he saw here as a home :sobe: just confessed but it's your tought not mine soo HAPPY NEW YEAR :D

Guys, which coordinator's contest was great this year, according to you? Mention them and give them a huge respect.

Only 4 Div4, XD. I have a friend who was only waiting for Div 4.

I like maomao90 and TheScrasse rounds.

Yeah it was quite tough though, as I solved the first five problems quite quickly, I mean I was able to solve them taking around 10 minutes each but when reached the problem 6 I had an hour left but still i couldn't solve it. I mean it was a fabulous problem.

However square the year was It was very square for me :D

Happy new year everyone! Wish you best of best! Thank you for everything Codeforces team! You are amazing!

Happy New Year, Codeforces! Hope you AC all the problems in life this year!

As I started new, these are my favourites: Watermelon (helped me start) Way too long words (my first own solved problem with no help) bit++ (took a long time but was solved)

Cute problems 2136E - By the Assignment 2096D - Wonderful Lightbulbs 2130E2 - Interactive RBS (Medium Version) Smashable problems 2154D - Catshock 2156D - Find the Last Number 2180C - XOR-factorization (ok this ones controversial but give it some love cmon) 2109D - D/D/D

I wish that i can be to Master in this Year (Hopefully)

I don't know whether these problems are interesting for GMs but for me they were one of the best problems I ever solved on codeforces: Minimizing the difference : https://codeforces.com/contest/1244/problem/E Big Brush : https://codeforces.com/problemset/problem/1638/D That's what I can remember right now.

I will shamefully advertise myself. I think https://codeforces.com/contest/2124/problem/H and https://codeforces.com/contest/2124/problem/I are the best and hardest problems I've ever authored (and probably will be the best and hardest problems I ever will).

#include <bits/stdc++.h> using namespace std; void solve(){ cout << "HAPPY NEW YEAR" << endl; } int main(){ int tt = 1; //cin >> tt; while(tt--){ solve(); } return 0; }

this person has more dedication than Lou Bloom in "Nightcrawler"

1672 -> 2108, +436. Pretty good, can't complain. Hoping for the best next year!

it was 0 and firstly i got 1057 but in last 3 contests i got minus and now 896

I don't think that's how fireworks work tho

I went from 0 -> 1565. This means... I had a +1565 increase!

i started codeforces few months ago and mine is 805 (max — 843)

I will also shamefully advertise myself. I think https://codeforces.com/contest/2159/problem/D2 is one of the best and hardest problems I've ever authored (though I don't think I can't make something harder than this).

some of my favourite problems from this year, some taught me new ideas, some other had me thinking about them for prolonged periods of time, some have very surprising solutions, because of their simplicity or because they need some creative combination. Spoiler

Bonne année, mes meilleurs vœux. Merci Codeforces pour 2025

To avoid overflows, it is better to use stoll instead of stoi.

convert string to lowercase for(char &c : s) c = tolower(c); convert string to uppercase for(char &c : s) c = toupper(c);

https://usaco.org/index.php?page=viewproblem2&cpid=1522 https://codeforces.com/contest/2159/problem/B (ik there exist really similar problems that would have probably made this less fun to solve, but I didn't know any of them, so it was really nice to solve, even if I did end up getting FST even with edi sol) https://codeforces.com/contest/2124/problem/E

Spoiler

I got +25 rating (1499 to 1524) from ~80 contests in 2025

These are my favourites: Trails (Hard) (Beautiful math) Removal Game (A friend asked me for the solution, but nobody in the room understood my explanation :() Mr. Kitayuta's Technology (Love how the author tricked me through example images) Happy coding!

https://codeforces.com/contest/2164/problem/B the most beautiful div2B I have ever solved https://codeforces.com/contest/2113/problem/C This problem had an amazing visualisation to get the solution I remember just going “OHHHHHHHHH” when I got the fullsolve idea for both of these problems, and subsequently having a really good mood throughout the rest of the day

Yeah absolutely right that's why I have mentioned to convert each letter.

My favourite problems: 1798E - Multitest Generator 2144E2 - Looking at Towers (difficult version) 2134E - Power Boxes 1738D - Permutation Addicts (the worst on this list because of my reading comprehension)

Thanks to all the teams responsible for competitions in 2025. Thanks for your hard work ! Looking forward to a more perfect competition in 2026!

I'll exclude my own problems, because I like all of them :) One problem from each difficulty 800-2200

Thanks! My personal favorite of my own problems is probably 2123D - Binary String Battle :)

I did not participate last year because there is no point in participating after turning 23

Great consistency. Can you please name the extension that used to generate the rating based heat map...?

Hope I become non — trusted participant in Div 3 this year

Went from 1052 to 1408, so I gained 356 points(could be 365 xD)

Super Awesome. I will do the same and try to attend 1 contest daily. I will save this blog and will try to update after a year about my status. Thanks for sharing and motivating!

Where can we submit our solutions? The replay contest doesn't seem to be accepting submissions.

also, for example, we can use transform, so if our string name s, it will look like this: transform(s.begin(),s.end(),s.begin(),::tolower) if you wanna to convert string to uppercase you will just change ::tolower to ::toupper, idk maybe your idea works fastly, also thank you.

I really liked the first 3 tasks in Good Bye 2025 and the first 4 in the latest Educational one. There was what I'm currently studying, dynamic programming, prefix sums, combinatorics, and these competitions also brought me into these topics.

https://codeforces.com/contest/2172/problem/H is a pretty fun exercise in the sense that you should look at all strings being compared and not just a pair. https://codeforces.com/contest/2155/problem/F in the sense it's just 506D in a different coating. https://codeforces.com/gym/105928/problem/E for being one of the most painful problems to implement. https://codeforces.com/contest/2153/problem/F for being very similar to 1771F. (Also I solved it in the contest) https://codefor

I hope some matches can be arranged in the near future.

ahsoltan who authored Order Capital Round 1 and reirugan who authored a couple of div 3's were some of my favourite rounds (despite me not performing well in them). Just loved the questions.

1748 -> 2116 So +368 this year, pretty good, hope this year is as sucessful

Please do not do this! Im rooting for you to get better at solving Div 2, but offing yourself for not reaching a goal is not a good mindset!

0+1620=1620 It has not yet converged. I hope I can get red name in 2026.

1716 after goodbye 2024. 1519 now. -197 lol. But it's okay, I started working this year and will probably gain it back within the next 3-4 contests.

from 619 ( 03.04.2025 ) to 1480 but max is 1550

How did you give a contest every day? Contests have so many gaps sometimes between them.

I hope I will achieve my dream in 2026 . Happy New Year and Wish for all lucky and happiness

+827 (bcz i just joined last year i only did 3 contests)

awoo I think there is a typo in editorial of Problem F1/F2, Instead of the following It should be this

Happy new year! I have participated in every traditional codeforces round in 2025 AUA. Great thanks to codeforces community and people work for it! Hope to see More rounds next year! XD

started in May got +1022, love the dopamine in solving problems

my approach for problem H. RobinHood I store all the unique elements of the array inside a temporary array (let's call it temp) and start traversing it. Let's say I am currently at an element with value $$$x$$$ and frequency $$$F[x]$$$, where $$$F$$$ is data structure used to store the frequency of elements (I used a map). The logic is as follows If I delete none of the occurrences of $$$x$$$, I get $$$F[x]$$$ occurrences to keep. If I decide to delete one occurrence of $$$x$$$

Consider this array 5 5 5 3 3 1 1 1 1 1 1. We can delete 5 5 3 3 and the final array will consist of 7 fives.

same dream bruh, I have the same goals but I think if I even reach candidate master, its good, and silver and gold are pretty far for me, cuz im only on 7th grade.

I am also interested... I want to go from pupil to expert

No way!!! O__O R u that YuukiS from r34 and pixiv?

+1608 :D (jk i started at September this year from 0 lol) Goodluck yall fellow coders! Wishing to get CM next year :<

My max was 1714 in 31/12/2025 and 2213 in 31/12/2026. so I gained +499.

can ppl outside india participate>?(and have a chance at the prices?)

This contest is a joke. I spent 3-4 hours finetuning parameter, estimate server's test cases scope, got rank 11, just for the next day to get pushed down to rank 38. And it's only been day 4!

How often do you actively tackle such tasks?

Usually for these adhoc contests, once my heuristics reach a state that I can't improve my solution anymore, I explore the tests and finetune constants like max iterations or leaves to get the highest score, and rerun many times to average the points. For this adhoc contest, not all tests are released so I submitted multiple times and estimate what the tests on the server covers. I don't think my approach for closed-set test cases adhoc contest is the proper approach, it's hacky but yeah, t

Read the rules again. Only one link that did not score 0 (for each participant) will be tested at the end. Therefore, selecting constants to pass the pre-tests is not a very good practice. This is my personal opinion.

Yeah I noticed that too, but I think the pre-tests have some traits of the final tests, so finetuning to pre-tests might generalize to edge cases in final tests. Also luck is 30% of the points as this is heuristics lol

1399->1851 +452 +1000 in 2026 pls.(hopefully not at the cost of my degree)

I was using another platform but for my country only, was 1300-1500, main div 2. Just started CF and it's so much more competitive here. Currently 0 -> 1037

0 -> 1803, +1803. If I continue like this, I'll be LGM on dec 10 2026 and beat codeforces all time high at march 28 2027.

not only it does never occur but i think it is also logically wrong because if you have more a[0] than "needed" then you can just keep picking decorations from a[0], until you finish all of them. I wonder if it is possible to hack that solution given "bad |= a[0] > z;".

From 1406 to 1822. I got +416 this year. Hoping for a better improvement next year.

https://codeforces.com/contest/2173/problem/C my first time solving a 1400 rated problem in a contest

These problems really felt educative and i liked it : 2176D - Fibonacci Paths 2175D - Wishing Cards 2145D - Inversion Value of a Permutation 2107D - Apple Tree Traversing Also, I would love to see these kinds of problem appear a little more this year : 2146D2 - Max Sum OR (Hard Version) 2149G - Buratsuta 3 2111E - Changing the String

Can someone, roughly, explain the time complexity of my code for D? This is the "optimal" one: https://codeforces.com/contest/2164/submission/356135976 And this is the non-optimal one: https://codeforces.com/contest/2164/submission/356135935 I'm not sure why both of them passed, as it seems like K * N to me(the final loop). I wrote the optimal one first, and it passed, so I decided to check if the l and r were necessary, somehow got the same runtime, so I resubmitted, and

Ohh, I didn't notice the multiplication. Thanks!

380C - Sereja and Brackets 1108E2 - Array and Segments (Hard version) First time i used Segtree here

Yeah, I can help. Read this: "When talking about XOR of a subsegment, it's usually useful to think about prefix XORs. Then, if bi=a1⊕a2⊕…⊕ai is the array or prefix XORs, the subsegment XOR f is simply f(x,y)=by⊕bx−1 . That means, for f(l,r) to be zero, bl−1 has to be equal to br , while all other values of b should be distinct. The easiest construction is then bi=i , with the exception that br=l−1 . The array a can be then reconstructed as ai=bi⊕bi−1 ."

Your strategy of computing binomial coefficients is incorrect. Why it is incorrect

Yeah, looks like this condition is redundant in this implementation of the solution. I think it remained from the previous implementation, where some other check was missing and this condition was needed in its place.

I was 2280 before 2025 and became 2133 at the end of the 2025 so it's -147. Although I reached my first IM and top rating was 2373 so it's half success I guess.

Yes, this is a typo. Thank you for noticing! Will be fixed in a couple of minutes.

A simpler solution/code for question 2131F - Unjust Binary Life {Question F unjust binary life}. Essentially the same concept but an easier implementation without the minimum to average part 356146228 Code

i started doing CP in April 2025 , and from that month i participated in 18 contests

why is almost nobody talking about problem D solution using ternary search

Thanks for all of you guys' hard work. This year is my very first year with codeforces and CP, even though I registered years ago. It is really happy to see my own progress day by day, week by week, month by month. By the way, my pleasure to the great Codeforces platform. I wish all of you guys a successful 2026!

$$$"here's$$$ $$$how$$$ $$$I$$$ $$$would$$$ $$$approach$$$ $$$it"$$$ bro let cf magic get to his head.

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It is showing this "Check email for login link. Kindly use the same browser." but I am not receiving the mail.

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Are these both online? (I can't find anything about APIO online on about Info1Cup in the site)

https://darkreader.org/help/en/ It say please pay for dark reader

Thank you guys so much because of inform me about dark reader!

Alright I actually change my mind, Im gonna learn some more optimization technique. Keeping with the current implementation doesn't seem to be the way

did you change your handle from axial tilted to employed?

1208C - Magic Grid The above problem is also based on this..

Huge respect and gratitude to everyone mentioned here As a participant, it’s easy to take contests for granted, but posts like this really highlight how much effort goes on behind the scenes — from problem authors and coordinators to hundreds of testers ensuring quality and fairness. Thank you for consistently delivering challenging, well-crafted rounds throughout the year. These contests are not just competitions, but learning milestones for so many of us. Wishing everyone involved a great

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is it possible to link this editorial in the gym page so it's easier to find?

I made a python script import requests curl = 'https://codeforces.com/api/contest.list?gym=false' r = requests.get(curl).json()['result'] for cid in r: if 'Div. 2' in cid['name'] or 'Goodbye' in cid['name'] or 'Hello' in cid['name']: url = f'https://codeforces.com/api/contest.standings?contestId={cid['id']}&from=1&count=1&showUnofficial=false' ps = requests.get(url).json()['result']['problems'] pC = ps[2]['name'] pD = ps[3]['name']

just wait a few days and it will disappear .

According to Ukrainian co-organizers( source in Ukrainian), EJOI is going to be held in Kaunas.

Top 2 teams from each of these regionals automatically qualify for WF Southeastern Europe (SEERC) Scoreboard Central Europe (CERC) Scoreboard Southwestern Europe (SWERC) Scoreboard Northwestern Europe (NWERC) Scoreboard

Wait outside or inside India? I am from the US and nobody calls it that :skull

1052 now i'm 1619 +567 . and will reach CM soon

As a "tester," I have yet to test the round

As a tester, I can confirm that the problems and cats are cute.

that's what poor people say. as a rich person i can entertain myself in more expensive ways

As a tester, I hope everyone can enjoy the first contest of the year.

same this was the first problem I thought of when I saw this blog post

Hello 2026! As a writer, I think that problems are interesting, have fun!

As a writer, I was amazed to discover that only 9 of the nine problems are truly excellent.

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After 30-50 minutes of thinking, read the editorial, but not the code. Then come back to the problem and solve it yourself. Also learning topics is needed, watch some videos about the topic you are uncertain about. Hope this helps!

as a friend of the writers (including the infamous pretender jiazhichen844 ), please upvote the announcement!

Do you have live rankings sheet satyam343 ?

Chinese round but not Chinese-friendly time...

Why is the start round $$$22$$$:$$$35$$$? Shouldn't it be $$$21$$$:$$$35^{UTC+7}$$$? UPD: It's fixed

https://youtube.com/live/4w4omqSg-GA?feature=share Checkout my stream :^)

There's lots of past olympiads in oj.uz , QOJ and Eolymp . There are also links here

A boolean can be toggled by XORing with true . Also if an integer is either 0 or x ( x is another integer) it can be toggled between 0 and x by XORing with x .

As a tester, I hope everyone enjoys the new year.

Can we get tourist to participate in this ;)

most of the task with xor can be solved independently for each bit

Can we get them to pariticipate in this then????

This is a meaningful problem because i have met many problems using these knowledge,though i haven't understand it

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"Ibrahim Fostok is better than me"

Did you give just "rated for Div1" contests? Or unrated for Div1 as well?

Well, communication isn't as bad as graders, and interactive problems

Wow,I know you at luogu,are you in kindergarten?

None of them are very bad if you practice. They can be much easier o harder than batch problems. (In fact, the most-solved problem of IOI was interactive and (I think) with functions) Btw, I recently made a powerpoint on problem types, you can find it here .

Precompute nCr with factorial + mod inverse Stars and Bars Inclusion–Exclusion

Here

Happy New Year! And it's a great contest as a gift for 2026, because A~F are very easy and G is challenging for advanced contestants.

Score updated !: 50 - 150 - 350 - 350 - 500

These are the same topics our teacher taught us in Combinatorics.

E was such a pain, I recognised LIS — knew had to handle consecutive same elements somehow. I only tried with sorting in increasing a and then increasing b. Editorial shows answer breaking ties by decreasing b?

If we have an array $$$P_0, P_1, P_2, \dots, P_N$$$, how to compute $$$\sum_{t=1}^{N}(1 - P_t)^{i - 1} \cdot P_t \cdot (1 - P_{t - 1})^{L - i}$$$ for each $$$i$$$ from $$$1$$$ to $$$L$$$ fast?

Original problem for E: https://www.luogu.com.cn/problem/P2782

This is what G made me think: [image]

Tysm, this will help my with my hate towards grader/interactive

Could you explain your request in more details?

Fun fact: the approach used for problem C described in the editorial has a well known name: Hamming codes. I'm unsure why the authors chose to leave this out. Anyway, there's also an awesome 3b1b video that describes the exact algorithm needed to solve this. Here's my code for reference. Also, a very similar idea shows up in this CSES problem , this EGOI problem , and the first suubtask of this CEOI problem .

CAN I PARTICICPATE IN THIS. AND IS IT FOR BEGINNERS?

Yes , you can participate by registering at Eolymp , It's more likely a Div.1.5 contest , the problems start with Div2A and ends with Div1B/C , the contest contains $$$5$$$ problems You can refer to previous Weekend Practice rounds for instance

This motives me to escape the expert-specialist hell I'm in, especially since I have less than 5x your problems made.

As a tester, the problemset is really nice. Recommend participating.

No problem! Feel free to message me if you have any questions

Personally I followed this when creating the communication problem for my round

yes , but i think it is mainly used in high rated questions

If you don't want to use dp, or just are computing nCr with non-prime mod for really large values, than CRT can be quite efficient.

The most important thing is to practice consistently. You will naturally slowly start to understand problems.

Improve your skill, don't look at streaks. Also, many useful blogs should be at the top of the Recent Actions instead of off-topic.

Let $$$a = [a_1, a_2, \ldots, a_n]$$$ be non-decreasing array of integers, then $$$\min_{i \neq j}(a_i \oplus a_j) = \min_{1 \leq i < n}(a_i \oplus a_{i + 1})$$$

want to be a expert by the end of 2026!! hope so

Person asked about his problems and ways to solve, why are you trying to humiliate him?

alcumus can teach you basics, then i would just do problems tagged combinatorics + dp, you should also know PIE

I'm sorry if I hurt you(extremely sorry). IlPrincipe . 🙏

Maybe on this contest, I can solve 5-6 problems and get rating of 1600.

Most advanced thing I used to get gold in 2025 was an ordered set. Problems last year were focused less on data structures (which is weird for EJOI). In all cases learn everything from syllabus but be ready for constructive and observation heavy problems.

Problem using this: 1625D - Binary Spiders

PieArmy orz

farkon00 orz

a == b : x x a ^= b : 0 x b ^= a : 0 x a ^= b : x x so it's valid

I want the value of that summation for each $$$i$$$ separately not the sum of it over all $$$i$$$.

Just go to this link and press "MAGIC" and press "HANDLE", you can change your username.