writing about it. That kind of communication takes a lot of energy — which I
currently don't, of work around the infrastructure. Unfortunately, I'm not very good at
delegating (though I manage
→ Pay attention
→ Top rated
| # | User | Rating |
|---|---|---|
| 1 | Benq | 3676 |
| 2 | Kevin114514 | 3659 |
| 3 | jiangly | 3640 |
| 4 | turmax | 3450 |
| 5 | tourist | 3408 |
| 6 | strapple | 3360 |
| 7 | Um_nik | 3354 |
| 8 | squareOf105 | 3348 |
| 9 | maroonrk | 3312 |
| 10 | idontwannadothis…e | 3191 |
→ Top contributors
| # | User | Contrib. |
|---|---|---|
| 1 | Qingyu | 154 |
| 2 | nik_exists | 151 |
| 3 | maspy | 149 |
| 4 | AmShZ | 146 |
| 5 | Um_nik | 143 |
| 6 | Errichto | 139 |
| 7 | BledDest | 136 |
| 8 | adamant | 135 |
| 9 | maroonrk | 133 |
| 10 | cry | 130 |
→ Find user
→ Recent actions
You can use several words in query to find by all of them at the same time. In addition, if you are lucky search understands word forms and some synonyms. It supports search by title and author. Examples:
305— search for 305, most probably it will find blogs about the Round 305andrew stankevich contests— search for words "andrew", "stankevich" and "contests" at the same timeuser:mikemirzayanov title:testlib— search containing "testlib" in title by MikeMirzayanov"vk cup"— use quotes to find phrase as istitle:educational— search in title
Results
1.
My Reply on "Mike, please stop ignoring your userbase" This is a response to [this post](https://codeforces.me/blog/entry/141442).
Originally, I intended to leave it as a comment, but the text turned out to be quite long. So I decided to publish it as a separate post.
Hi!
Let me start with the main idea: I don't think I ignore too many issues (though I do ignore some). In most cases, I do work on them, but these days I just don't feel like writing about it. That kind of communication takes a lot of energy — which I currently don't have.
Oh, it looks like you edited the beginning of the blog, and now it triggers less of an internal protest in me. Honestly, lately I've been in
a difficult emotional state, and I just don't have the energy or desire to interact much. It's not just about Codeforces — it's generally harder for me to engage than it used to be. I won't go into details (health, relocation, family issues, changes in the nature of my work due to bots) — all of that affects my mental state and willingne...
2.
I am Mike Mirzayanov. AMA! <img src="/predownloaded/3f/31/3f31c3ac1f7b4e53128fc9708f5736eea40d7b94.jpg" style="width:250px; margin:1em 0 0 0; float:right;"/>
But why not!
Many people here seem to know me. Or maybe not quite? I am ready to answer your questions. Ask me anything! I plan to spend no more than 3 hours on answers. Sorry if I can't answer all the questions.
Let's more or less follow the rules from here https://www.reddit.com/r/IAmA/wiki/index
Below is actually a quote from the rules.
The interviewee begins the process by starting a post, describing who they are and what they do. Then commenters from across the internet leave questions and can vote on other questions according to which they would like to see answered.
The interviewee can go through and reply to the questions they find interesting and easily see those questions the internet is dying to have the answer to.
Because the internet is asking the questions, they're going to be a mix of serious and lighthearted, and you'll ...
Because the internet is asking the questions, they're going to be a mix of
serious and lighthearted, internet is asking the questions, they're going to be a mix of serious and
lighthearted, and you'll
3.
A List of Useful Equations in Competitive Programming Hi, I am super excited to be back with another list. This time it is a **collection of some useful equations in Competitive Programming**.
### Motivation
Do you find it bad if you couldn’t solve a problem just because you didn’t know about a certain equation?
Do you find it difficult to take a quick look at an equation that you know exists but forgot about it while solving a problem?
Do you think that all the equations that are important in CP are just cluttered and you are too lazy to collect them in one place?
Well, then you are in the right place! I am here to solve all of the aforementioned problems. I believe you should not waste your precious time searching the internet for important equations. You should solve more problems. I am here to undertake the nasty task of collecting things.
### Payment
Everything comes with a cost. You need to do something for me. That is you need to upvote this blog. Pretty easy!
### Acknowledgement
Thanks to the following guys ...
A List of Useful Equations in Competitive Programming, Hi, I am super excited to be back with another list. This time it is a
**collectionof some useful, Well, then you are in the right place! I am here to solve all of the
aforementioned problems. I
4.
[Repost] "Justice may be delayed, but it cannot be absent": New Evidence on
NXIST's Cheating Scandal
[Repost] "Justice may be delayed, but it cannot be absent": New Evidence on NXIST's Cheating Scandal _Original post: [「正义可以迟来但不能缺席」：关于 NXIST 的一些新证据](https://zhuanlan.zhihu.com/p/620297880)_
_Translated by GPT-4 with some adjustment. Please inform me if there are any mistakes._
_All links to the invalid repository have been redirected to the backup repository._
**This article provides a logically complete set of evidence, which does not involve any non-public internet resources, regarding the "suspected cheating" incident involving the ICPC Yinchuan Station and ICPC Shenyang Station in 2021. By discovering the suspected GitHub account ([NaokiLH](https://github.com/NaokiLH), renamed to https://github.com/brokenTarget) of a team member from Ningxia Institute of Science and Technology (NXIST) TS 1 team, Lan Hao, two years ago, and by mining and analyzing the commit records of his algorithm competition repo, we have obtained direct evidence that at least 4 questions from the 2021 Yinchuan regional contest set and at least 6 questions (including scrapped questions) from the 2021 Sh...
logically complete set of evidence, which does not involve any non-public
internet resources
5.
Blogewoosh #7 Hello, codeforces!
Long time no see, right? So maybe it's a good idea to try to return to my blogs slowly. This time the blog will be about a trick, which usually isn't necessary to solve a task, but can be useful to make implementation much more comfortable.
Let's look at [this](https://codeforces.me/contest/932/problem/F) problem. It is about some DP on a tree in which we have to use convex hull trick to improve the complexity. The task requires merging two convex hulls with "smaller to bigger" trick. I recommend you to read the statement before reading the rest of the blog (and the [editorial](https://codeforces.me/blog/entry/57796) if you don't know how to solve it).
[cut]
$ $
So, how to merge two convex hulls? If we keep them in something like the set from C++, then we can just take every element from the smaller one and try to add it to the bigger one. Unfortunately, adding one element in this way requires some ifology and care. It's hard to implement it, especiall...
to bigger" trick. I recommend you to read the statement before reading the rest
of the blog (and the
6.
The Ultimate Equation List This is **a collection of all important equations in Competitive Programming**.
# Motivation
Do you find it bad if you couldn’t solve a problem just because you didn’t know about a certain equation?
Do you find it difficult to take a quick look at an equation that you know exists but forgot about it while solving a problem?
Do you think that all the equations that are important in CP are just cluttered and you are too lazy to collect them in one place?
Well, then you are in the right place! I am here to solve all of the aforementioned problems. I believe you should not waste your precious time searching the internet for important equations. You should solve more problems. I am here to undertake the nasty task of collecting things.
# The Equation List
1. Axiom of extensionality: $\forall x\forall y[\forall z(z\in x\Leftrightarrow z\in y)\Rightarrow x=y]$
2. Axiom of regularity: $\forall x[\exists a(a\in x)\Rightarrow\exists y(y\in x\land\lnot\exists z(z\in y\lan...
This is **a collection of all important equations in Competitive Programming**.
# Motivation, Well, then you are in the right place! I am here to solve all of the
aforementioned problems. I
7.
Round 449 statements (warning: butthurt) If you don't wanna see some butthurt, skip this post.
1 December: I open main page of codeforces to see a picture of some anime girl taking half of my 1920x1080 screen. I got disgusted back than, but hatred for anime is my personal opinion, but IMO this picture was way too big to be on the main page of CF(it was the biggest one I saw on CF, if i remember correctly).
2 December: after nice Trial Round of NEERC I was looking forward to a CF round. I was not in my hometown and had internet which was LTE, but still was kind of laggy and slow. I was checking in in the hotel at the time of start of the round.
So the round starts, problem A loads, and here we go. There is another f***g anime picture right in front of me (which loads slowly because of internet, and the statement isn't loading until the picture loads (it generally isn't that way though)). Name -> Picture -> Statement. At this point i instantly added some curse words in my template (luckily i decided not to compete, so...
Trial Round of NEERC I was looking forward to a CF round. I was not in my
hometown and hadinternet
8.
About Rating Changes in AtCoder. TL;DR
What if we introduce the followings:
- You'll have a register-as-unrated button. You can switch rated and unrated only before opening a problem.
- If you are registered as a rated participant, you'll get rated when you open a problem, even if you don't submit.
Hello, community.
Currently, your AtCoder rating changes only if you submit to the contest.
This is also the case with Codeforces, so I think it's a standard.
However, this scheme clearly has a flaw; you can leave the contest without submission to keep your rating.
This implies you may get underrated because of those who didn't submit.
You would say things like this can happen only if you are a newcomer, and the effect will be negligible in the long term.
I generally agree with it, but sometimes even reds are affected by this issue.
I know some people intentionally submit CE code to make them rated.
At the same time, I know some people do the "Head to F" strategy or similar things and sometimes don't m...
the contest without submission to keep your rating. This implies you may get
underrated becauseof
9.
Sad story of one commit So, first of all, I would like to apologize for the issue with the problem B in today's ER. We tried to fix it as quick as possible, but unfortunately, still lots of submissions were made and this caused a big queue during the round. I am sorry for this.
How did this all happen? Well, this is really a sad story about one commit.
About three hours before the round, while writing explanations for the problem B statement, I noticed that the answers were different from the correct values by 1. I opened the model solution in another tab in Polygon, wrote +1 to the value I printed, clicked "Save" and then committed the changes (including the notes for the samples). But, unfortunately, that change in the model solution wasn't included in the commit.
The cause was that the model solution didn't save in time for the commit (and actually never saved for some reason, maybe some bug in the browser or Internet connection issues). I didn't notice that, and while rereading the problem again,...
Sad story of one commit, for some reason, maybe some bug in the browser or Internet connection issues).
I didn't notice that, So, first of all, I would like to apologize for the issue with the problem B in
today's ER. We
10.
One final blog about Codeforces Round 1033 and CodeNite 2025 Hi everyone, writing this blog after the recent rollback, getting red back to top of leaderboard as everyone so much desired, and making the overall leaderboard so much better.
If you disliked the announcement/tutorial of [contest:2120] or posted a genuine critique because of problem quality or or because of some other situation which we could've improved, then this blog is not for you, I don't have any hard feelings and understand why you did it.
The dark side
------------------
First of all, everyone who cheated in the round, I really reprimand you all and hope you all are fairly retributed for what you all made me go through and the deeds you've done. I especially hope all those who run the back alley solution distribution during the contest are gone for good and that they are especially retributed for their wrongdoings. (I don't think we can stop GPT or that it can suffer "retribution", so not sure what to say about it. Anyways, people who use GPT for wrong are responsib...
But hey, I won't only show the dark side. **A thank you from the bottom of my
heart** really for, Hi everyone, writing this blog after the recent rollback, getting red back to
topof leaderboard as
11.
Chinese Postman Problem: How I Ran a 180 km Ultramarathon Through Every Street in My City Hello, Codeforces!
A couple of years ago, a friend of mine told me that two cyclists had passed through every single street in the center region of the city I live in (Belo Horizonte, southeastern Brazil), on the [third try](https://www.strava.com/activities/1030665876/overview).
<spoiler summary="First try">
After ~160 km, they had not completed 1/3 of the goal. [Strava link](https://www.strava.com/activities/976021527).
<img src="/predownloaded/8a/53/8a53829f7d78e88808a3ff751b64406ec2fc0efd.png" style="width: 600.0px;max-width: 100.0%;max-height: 100.0%;">
</spoiler>
<spoiler summary="Second try">
They were better prepared, but one of the guys was run over by a car (no big injuries). [Strava link](https://www.strava.com/activities/999450285).
<img src="/predownloaded/85/8f/858fdcdcfda93cd1d9c7c59db7dbfad9e63d6ea2.png" style="width: 600.0px;max-width: 100.0%;max-height: 100.0%;">
</spoiler>
<center>
<img src="/predownloaded/8d/5c/8d5cfb677a361654105e49f36f214c35...
Blossom from the internet [2], I implemented the algorithm and got an optimum
route outof it. And
12.
Creating Gravity Defied tracks using Codeforces rating graph Introduction
============
<img src="http://cs624422.vk.me/v624422694/36ac0/8jKq7pMzPOc.jpg" style="float: right;"></img>
Hi everybody! Recently I have decided to refresh memories about good old times and play Gravity Defied on my phone. It wasn't really hard to find port of that legendary game from J2ME to modern platforms. It rapidly gained glory among students of past decade. Key points of Gravity Defied success were nice gameplay (biker completing different stages with high cliffs and deep pits), convinient physics (ability to rotate mid-air) and simplicity of modmaking. As for me, it was a bit more than usual game. When I had completed over thousand tracks, I began earning money on helping others to progress. Only later even more difficult games were developed: HOMM 3, Far Cry and Dark Souls...
Predevel story
============
<img src="http://cs624422.vk.me/v624422694/370dd/wU1hi77t6U8.jpg" style="float: right;"></img>
And now Gravity Defied is on my phone again! Not o...
old times and play Gravity Defied on my phone. It wasn't really hard to find
portof that legendary, When I finally start to think about general concept of program, I realized that
I know nothing
13.
The history of some recurring problem Hi everyone! This one will be long and contain a lot of off-topic, prepare yourself (or skip down to solution of mentioned problem)!
### Intro
In this blog post I would like to talk about some problem that somehow was on my mind for several years and yet only now I have some more or less complete understanding of how to deal with it. The problem is as follows:
_You're given string $S$ and $q$ queries. In each query you have to count amount of distinct substrings of $S[l,r]$._
[cut]
<br><br>
Since then and for a long time this one was probably the hardest string problem I could ever imagine. In particular I saw some partial cases of it on several judges, which supported my assumption that problem is particularly tough. Some notable examples:
- [To Queue or not to Queue](https://www.codechef.com/problems/TMP01) on codechef by [user:Gerald,2018-08-24]. It is the same problem, but queries are formed as queue, i.e. you have to add letter to the right, delete letters from th...
The history of some recurring problem, - [user:I_love_natalia,2018-08-24], for being that kind of weirdo who accepts
friend requests from, Hi everyone! This one will be long and contain a lot of off-topic, prepare
yourself (or skip down
14.
Catching the Mole II(Hard Version) (Psychotic_D cheating case aftermath) This is a part 2 of [my other blog](https://codeforces.me/blog/entry/131821) on the [user:Psychotic_D,2024-07-23] situation. I highly recommend you see it before this one for context.
If you don't care that much, here is a quick recap of what was covered in the other blog before we get started: [user:Psychotic_D,2024-07-23] had a ridiculously good performance on his friend's ([user:wuhudsm,2024-07-23]) round. This let many people become suspicious of whether he achieved this legitimately. Then multiple accusations were thrown around and I did my blog doing my own investigation and compiling the most compelling evidence I found. The takeaway was that [user:Psychotic_D,2024-07-23] was probably cheating along [user:EndlessDreams,2024-07-23], who would give him code for [user:Psychotic_D,2024-07-23] to copy. [user:Psychotic_D,2024-07-23] would alter them heavily to avoid plagiarism, but it was clear beyond a reasonable doubt that he was cheating.
Well, I finished writing that blog, ...
the internet for a problem. It ended up being that
[user:amenotiomoi,2024-07-23] was the sourceof
15.
I will be doing 24h livestream during Marathon24 and I need your ideas! (all of you!) <b>Updated on 07/12 for the last time</b>
* [Postmortem](http://psyho.gg/postmortem-about-the-24h-livestream/) -- explains a lot of stuff and it might help you decide if there's any point in watching this
* [Twitch stream](http://www.twitch.tv/fakepsyho/c/7041087) -- original livestream
* [YT mirror](https://www.youtube.com/watch?v=ovtLuqgM3rA) -- because for some reason a lot of people wanted it
If you have any feedback (bad or good, doesn't matter as long as it's constructive), I'll be more than happy to hear it. Especially since I might do more of these (just not that long).
<b>Updated on 27/11, because it got into "recent actions"</b>
The stream will happen [28/11 Saturday 9:15 AM GMT+1 to 29/11 Sunday 10:15 AM GMT+1](http://www.timeanddate.com/worldclock/fixedtime.html?msg=24h+Livestream+by+Psyho+during+Marathon24+finals&iso=20151128T0915&p1=3903&ah=23&am=59)
The address for the stream is [http://www.twitch.tv/fakepsyho](http://www.twitch.tv/fakepsyho) — ye...
I will be doing 24h livestream during Marathon24 and I need your ideas! (all of
you!), the contest would require the participants to have no internet connection. The
otherthing is that, ). Unfortunately, this means that the contest would require the participants to
have nointernet connection. The
16.
FAQ, Advice & AMA This post assumes you're super ambitious.
But don't take any advice too seriously -- we're all different. This is simply what worked for me and might work for you. Choose your own path.
#### Useful Links
- [LI2 Contests](https://codeforces.me/blog/entry/131164) -- used this course when I was starting out.
- [usaco.guide](usaco.guide) -- a collection of great articles & problems on almost all topics.
- [OI Checklist](https://docs.google.com/spreadsheets/d/15b1ZaP1owTfTcA4vQ69A5S_wUd_vJmM8Slwu6FiWgP4/edit?usp=sharing) -- my OI Checklist.
- [Pavel Mavrin's youtube channel](https://www.youtube.com/channel/UC9WDkCyUlNTncq1Y-mFSgLQ) -- watched his great lectures when I was younger :)
- [qoj.ac](qoj.ac), [loj.ac](loj.ac), [dmoj.ca](dmoj.ca), [oj.uz](dmoj.ca), ...
#### How do I start?
**Advice:** join a great community (school, club, ...), try solving problems, and find someone who can answer your silly questions.
I wouldn't have started CP if not for my school. Of c...
the last cool thing you do. "The ability to play chess is the sign of a
gentleman. The ability
17.
Please, give us proper explanations about this nonsense. It has been brought up a few times already:
- [Submission pages on Codeforces often not loading](https://codeforces.me/blog/entry/134655)
- [Unreasonable delay for viewing submissions](https://codeforces.me/blog/entry/135457)
Ok, so, this time [I just tried a bunch of hacks on some submissions that were very close to the time limit](https://codeforces.me/contest/2042/hacks?verdictName=&chosenProblemIndex=D). And now **I couldn't access to a single submission page for around 20 minutes straight.**
Did I do something that terrible? Is it against the rules? Did it harm the server so much?
I mean, it could be bad for the server for reasons I don't know, but the thing is **this whole nonsense has never been explained**, why such a restriction has to exist and what bad things it even causes, even after several requests from many people. There has also been no single attempt to specify a visible rule or policy about opening submission pages, and many many people are just getti...
://codeforces.com/blog/entry/135457) Ok, so, this time [I just tried a bunch of
hacks on some, I mean, it could be bad for the server for reasons I don't know, but the thing
is **this whole
18.
MIT Mystery Hunt Disclaimer: This blog is not about competitive programming; you probably will not learn anything about algorithms and data structures. In other words, it doesn't qualify for [this initiative](https://codeforces.me/blog/entry/110840), but I want to give a link to it anyways because I think it's cool.
I love solving problems. No, seriously. I LOVE it. The mindset described in [this blog](https://codeforces.me/blog/entry/91114) is 100% how I feel. But it is not constrained to competitive programming problems. I loved math problems for a much longer time, and physics was somewhere there. But I also love solving puzzles. And playing puzzle games on the computer (well, on consoles). And participating in intellectual games. I am not as good in them as in cp, but it was never about being good for me, I just love the process.
And I think that there might be some people with a similar love for puzzles among competitive programmers, this is why I decided to write this blog on CF <s>and no...
not because this is the only place on the Internet where my opinion matters a
little. So
19.
Rumination on AI and competitive programming An OpenAI model can now achieve a rating of 1800 in Codeforces. That made me wonder about the future of competitive programming and why we do this. I came up with some opinions, which I'll be glad to share with you.
## AI killed the competitive programming?
I don't think that's happening, because competitive programming is useless! Some people might think CP is less interesting because AI can solve CP problems — but come on, problemsetter can solve those problems, unless they are really bad. Many people still play Chess just fine, and I recently enjoyed participating in Sudoku competitions, although I was completely aware that computers would wreck me in a second. It didn't matter, and I didn't see how it could.
CP problems are not "open problems" — if they are, the problemsetters are to blame. So, you are not contributing anything to the world by solving CP problems; it all comes down to personal interest. As long as CP is fun for people, they will do it.
## Flag...
having such a high rating, so this is indeed a bad thing. I also think the idea
of "infinite
20.
Is university degree important? <HTML>
<HEAD>
<META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8">
<TITLE></TITLE>
<META NAME="GENERATOR" CONTENT="LibreOffice 4.1.6.2 (Linux)">
<META NAME="CREATED" CONTENT="20091123;224100000000000">
<META NAME="CHANGEDBY" CONTENT="Mahmoud Hassan">
<META NAME="CHANGED" CONTENT="20160315;170001200000000">
<META NAME="AppVersion" CONTENT="00.0001">
<META NAME="DocSecurity" CONTENT="0">
<META NAME="HyperlinksChanged" CONTENT="false">
<META NAME="LinksUpToDate" CONTENT="false">
<META NAME="ScaleCrop" CONTENT="false">
<META NAME="ShareDoc" CONTENT="false">
<STYLE TYPE="text/css">
<!--
@page { size: 8.5in 11in; margin: 1in }
P { margin-bottom: 0.08in; direction: ltr; widows: 2; orphans: 2 }
-->
</STYLE>
</HEAD>
<BODY LANG="en-US" DIR="LTR">
<P STYLE="margin-bottom: 0.14in">I was going to write a short post
asking you about your opinion on the importance of university degree
but ended up writing a really long text about the educatio...
everything you need from the Internet. The only thing that would interest me
in the university (as, what I see you can learn pretty much everything you need from the Internet.
The onlything that
21.
Tutorial: The fastest tree algorithm, the XOR Linked Tree Hi Codeforces!
This is a blog about a really cool folklore technique that seems to have been forgotten over time. I currently only know of one place where it is mentioned on the internet, https://www.algonotes.com/en/minimal-memory-dp/, which is a tutorial by [user:monsoon,2024-10-20] for his problem "Matchings" https://dmoj.ca/problem/ontak2010sko from a POI training camp in 2010 ([see this for more information](https://codeforces.me/blog/entry/92090?#comment-807964)). But I've heard that this technique is even older than that. I originally learnt of this technique a couple of years back when I was digging through the fastest submissions on [problem:321-C] and I saw it being used in a submission [submission:9076307] by [user:Marcin_smu,2024-10-18] from 2014.
I don't know if there is a name for this technique, so I've decided to call it the _XOR Linked Tree_ because of its close connection to XOR linked lists https://en.wikipedia.org/wiki/XOR_linked_list.
The XOR Linked Tree is...
forgotten over time. I currently only know of one place where it is mentioned
on theinternet, https
22.
Cost-Benefit Flow ## Motivation
By chance, I stumbled upon the blog post by [user:errorgorn,2025-11-22] titled [Solving Problems with Min Cut Max Flow Duality](https://codeforces.me/blog/entry/136761). When they mentioned using flow (for certain problems) in a similar way to 2SAT, something clicked for me. While I knew how to solve a variety of flow problems along with forming certain flow networks ad hoc, there was this entire subset of flow problems which I previously did not understand how to do.
The blog post does a great job of explaining many of the concepts/applications, but there were certain things that got black-boxed. In order to understand things, my brain works such that truly understanding what is going on under the hood (often through proofs) helps me better intuit how to use ~~and abuse~~ a tool. Naturally, I tried to search the internet for more information on this topic. Unfortunately, I quickly came to realize that not much material as in-depth as the aforementioned blog p...
. While I knew how to solve a variety of flow problems along with forming
certain flow networks ad hoc, The blog post does a great job of explaining many of the concepts/applications,
but there were
23.
What not to say when you are accused of cheating `Hi! I got a message stating that "Your solution 123456789 for the problem 9999H significantly coincides with solutions tourist/987654321, jiangly/987654322."`
Anyone who has looked that [that one blog](https://codeforces.me/blog/entry/8790) has seen numerous comments like this. Obviously, except for a few cases, no change has been carried out.
Of course, sometimes you didn't cheat, and you followed all the regulations. **False positives happen.**
Here are some things that you **shouldn't** (and **should**) say in order to make a genuine request for Mike to review your case.
### 1. do **NOT** over-emphasise your rating.
"pls pls pls give my rating back (emoji) i need it i was so close to expert"
First of all, it feels fake.
Besides, obsessing over rating is a common trait of cheaters — if you aren't cheating, you can get the rating back in a few rounds anyways. What's the worst that could happen? You could get back anyways, _if you aren't cheating._
### 2...
What not to say when you are accused of cheating, , except for a few cases, no change has been carried out. Of course, sometimes
you didn't cheat, and
24.
A Beautiful Technique for Some XOR Related Problems ## Inspiration
I'm very excited about this blog, as it took me quite a lot of effort and scavenging through the internet to completely grasp the concept of this technique(That's probably because I have almost zero knowledge in Linear Algebra or I'm just plain dumb). So I feel like I genuinely conquered a challenge, and I really want to share it with someone. But there's no way my CP friends circle will believe it, they'll think I'm just trying to show off :P
So here I am, sharing it on CF. I also created a [personal blog](https://drschwad.github.io/), so that if I ever feel like sharing something again(not only about CP), I can write a blog there. I also added this same post [there](https://drschwad.github.io/2019-08-06-z2-space-xor-trick/), you can read it there if you prefer dark theme. I'll be pleased to hear any thoughts on the blog or if I can improve it in some way ^\_^
## Introduction
Since it concerns Linear Algebra, there needs to be a lot of formal stuff going on ...
scavenging through the internet to completely grasp the concept of this
technique(That's probably because I
25.
Competitive Programming in the Era of AI **Read the original post on :** https://www.vibhaas.net/posts/Competitive-Programming-in-the-era-of-AI/
<br>
<div align="center">
<img src="/predownloaded/3e/ae/3eaee0e93cf1784ab4923157729c81dd3a080fcf.jpg"
alt="Wanderer above the Sea of Fog, Caspar David Friedrich"
width="70%">
<br>
<small><i>Wanderer above the Sea of Fog, Caspar David Friedrich</i></small>
</div>
<blockquote>
Picture this. You've had a draining week at university or at work. You're exhausted, and you need a break. Most people would play a few video games, grab a few beers with their friends, or just sleep. But you have the (mis?)-fortune of being addicted to this weird, aesthetically questionable website called Codeforces (or AtCoder, or whatever your favorite OJ is).
</blockquote>
<blockquote>
You check the list of upcoming contests, and you're in luck. "Nice," you think to yourself, "two rated contests back to back!" This is going to allow you to farm some rating! ...
Competitive Programming in the Era of AI, get your weekly fill of validation (or disappointment) from these random
internet points. Still, at
26.
On Div2ABs 2 years ago, [user:antontrygubO_o,2022-04-27] wrote [a blog](https://codeforces.me/blog/entry/75163) about div2ABs where he expressed his opinions that d2ABs should not be about "here is a statement, please implement what is written there". Thanks to him, the quality of d2ABs (and problem quality in general) have certainly improved. However, I still believe that there still quite large differences between how coordinators/problemsetters view d2ABs and how the intended participants view them.
From the survey made by [user:kpw29,2022-04-27], we can see that most people agree that most people agree that we should **primarily** consider the target audience when proposing a task. I too think if a task is boring to div 1 contestants, we should not think of that as a reason to immediately disqualify a problem from being a d2A.
I think when people judge the interesting-ness of d2As, they try...
statement directs to a external page(thus factor of internet connection, and
understanding what OR is for
27.
Witchhunt forces The cheating allegations in this community are getting ridiculous
[Blog](https://codeforces.me/blog/entry/154155)
Note how in here, multiple people were calling out other people who performed well for cheating with minimal, or in these cases no evidence. Firstly the poster instantly got accused by some random guy???? bro doubled down and tripled down on it too all because of a single comment. Yes, while its rare, some people do write down their thoughts inside their code, this is down to personal preference
Apparently trying to clear up confusion about the situation = "Also, if you really weren't using AI, would you have edited this 5 times to desperately try to prove your legitimacy?"???? Yes because legitimate users would totally go "yeah i cheated" instead of trying to clarify that they're legit.
Now next up, rating growth = cheating apparently too, based on another user later down that blog. "Oh you got +200 in 2 months? cool did you change up how you practice, did you g...
internet point". I'm aware I only showed one blog, but there's been multiple of
them up to this
28.
[Tutorial] On Applications of CDQ Divide & Conquer _This tutorial is nominated for the [blog posts competition](https://codeforces.me/blog/entry/149422) from [user:cadmiumky,2026-02-07]. Thanks to him for this initiative!_
_Also thanks to [user:Ghos007,2026-02-08], [user:dima210121012101,2026-02-08], [user:dmitryAdams,2026-02-08] and ChatGPT for proofreading this post and giving useful feedback._
---
CDQ Divide & Conquer is an interesting algorithmic technique that nobody talks about (at least in Russian CP community). However, it is quite powerful, as it often provides unexpectedly clean solutions to seemingly tedious problems. In this tutorial, I will discuss different contexts where this method is useful. I also want to collect what I have seen about this technique on the Internet in one place and add my own insights. Credit to [robert1003's blog](https://robert1003.github.io/2020/01/31/cdq-divide-and-conquer.html) where I first learned this method.
The main idea of this technique is to calculate the **influence/contr...
[Tutorial] On Applications of CDQ Divide & Conquer, collect what I have seen about this technique on the Internet in one place and
add my own insights
29.
How optimal is your CP setup? Click here and find it out! Recently I thought a lot about optimizing my setup. I don't think it is an important aspect of cp, as it barely affects the performance, but it is fun to think about nonetheless.
In this blog, you will be able to determine whether you have an optimal setup or not. I will list the criteria and points you get for satisfying each one of them. In the end, I do the breakdown for different point ranges.
I won't include things like **having a monitor** or **having an internet connection**, but I will be including basically everything else that comes to my mind. If you see something missing from the list, let me know in the comments, I will probably update my list then.
This blog is mainly made for laughs, but if you are new, you will probably learn something new, even though **it won't help you to increase your rating**.
### You can compile and run your code.
- $0$ points: I don't know how to run my code before submitting
- $10$ points: I compile my code b...
30.
PSA: don't feed the trolls! Regarding the recent events, there have been a lot of genuine comments from all sides, and although we may not agree with many of them, they are still someone's legitimate opinions. But there has also been an increase in people who are not saying what they really think. Instead, they are writing deliberately to provoke an emotional response. Most of them are probably doing it for fun, but there is also the chance that some might try to get something out of it.
It is fascinating to me that the internet has had at least 25 years of experience with trolls and everyone still does the one thing they should not do: feeding the trolls. Actually, people seem to be barely familiar with the concept as a whole. The meaning of the word has been diluted a lot due to improper usage. When [user:rotavirus,2022-02-28] was banned, in the discussion that followed, very few people seemed to realize that he did what he did for exactly this purpose.
Let me first reiterate what a troll is. A _troll_ is...
the internet has had at least 25 years of experience with trolls and everyone
still does the onething, It is fascinating to me that the internet has had at least 25 years of
experience with trolls and
31.
Stop Putting Large Data Sculptures or Special algorithms In Div2D/E If your don't agree with this blog,have a better way dealing with this kind of problems,or think i need to improve my blog skills,just tell me at the comments
Sorry for my poor English skills:(
I cant bear more.I have to write a blog about it.
Eaxmples
==================
[1557D](https://codeforces.ml/contest/1557/problem/D)
[1555E](https://codeforces.ml/contest/1555/problem/E)
[1549D](https://codeforces.ml/contest/1549/problem/D)
[1557C](https://codeforces.ml/problemset/problem/1557/C)-calculating C(a,b)in log(n)'s time
[1550D](https://codeforces.ml/problemset/problem/1550/D)
What's wrong on these problems
==================
I started programming on cf because my friends told me that cf problems need coders's thinking more than coding.
But now things started to change.
These problem can just stop coders from solving them because they don't know a certain algorithm,even if they found the correct way of solving them.
What's more,most of these problems' ...
imagine in your internet explorer to use anytime in any contest if this kind of
problemsetting
32.
Code Festival 2016: interview and photos from participants [Code Festival 2016](http://codeforces.me/blog/entry/48616) was held in Tokyo on 25-30 of November. Boris [user:qwerty787788,2016-12-13] Minaev has shared with us his impressions, and Maxim [user:Zlobober,2016-12-13] Ahmedov and Nicolay [user:KAN,2016-12-13] Kalinin shared photos.
— _To start with, let's mention that,_ [AtCoder](https://atcoder.jp/) _and_ [Indeed company](http://ru.indeed.com/about) _announced the festival. How many quals were there? In what way were they arranged?_
— There were 3 contests, in which you could take part. In the first part TOP-10 were selected, in the second one — TOP-5, the third one — TOP-5. To sum up, there are 20 foreigners to be selected.
— _Which quals the Japanese had then?_
— Probably the same, but 200 participants passed the qual there.
— _That means, the event is more orientated on Japanese people?_
— The previous years the event was held only for Japanese, this year they decided ...
[Code Festival 2016](http://codeforces.me/blog/entry/48616) was held in Tokyo
on 25-30of November
33.
AI might erase CP, but not us I haven't slept for 20 hours and I can't fall asleep. I've been reading others' topics on AI, and I had a sort of epiphany. These ideas have been brewing inside me for many years, and I thought it might be time to share them with the community.
---
There were times when I was a "competitive programmer" at the core. I spent many years doing that exclusively. I've never been to IOI, but I like to think that I've reached some good heights.
Two years ago, I stopped writing online competitions. I've written a few offline competitions after that, but eventually, I decided to stop that too.
Yet somehow Codeforces still attracts me. I don't want to solve problems, but I keep typing codeforces.com into the address bar. *Why?* Just yesterday, I didn't have an answer.
---
Imagine a layperson asking you what competitive programming is. What are you going to say? My answer has always been "Oh, we solve interesting algorithmic problems with time constraints and other limits". Many ...
had a sort of epiphany. These ideas have been brewing inside me for many
years, and I thought it
34.
NERC online Greetings to every one who's looking forward to take part in NERC 2020. Many of you cold have seen [the Special Regulation Rules for ICPC NERC in 2020/2021 Season](http://neerc.ifmo.ru/information/contest-rules-2020.html).
In a nutshell -- quarterfinals (regional contests) can be held either online or offline (organizers consider that), half-finals (Northern Eurasia Finals) are held striclty online, each team can use three PCs, each team can use the Internet freely, it's not mandatory for a team to gather in line room, there's no proctoring system at all. Also best teams of NEF will advance to World Finals 2021 Selection Round, its exact rules are not yet known. So, some kind of a rehearsal before Super Regional Finals that should come in effect in 2026 or later.
And completely another situation in [the special rules](https://neerc.ifmo.ru/school/russia-team/rules-2020.html) for Russian School Team Contest (RSTC?) for the same year -- it's held online but any team should gather ...
in one place, should use only one PC and only a set of specific Internet
pages. Also there's a
35.
The end of the 5th place curse in Turkish Team Selection Contest [user:kalimm,2026-06-03]
[user:TahsinEnesKuru,2026-06-03]
[user:AhmetKaan,2026-06-03]
[user:erkam,2026-06-03]
[user:ayhan23,2026-06-03]
Five people, five 5th placers... Brightest minds of Turkiye with one mutual dream: representing their country at IOI. Countless hours spent coding, debugging and studying towards their goal. But little did they know, **[they](https://codeforces.me/blog/entry/54007) [were](https://codeforces.me/blog/entry/66811) [cursed](https://codeforces.me/blog/entry/116387)**. All of them came very close to getting into the team, closest you can get to it actually but the 5th place curse would not let it happen.
What does this curse do? Well every IOI team has 4 participants in it, each of them finishing in the top 4 in their country's team selection. When you finish in 5th place, its a very heartbreaking situation but unless its your last year, its actually not so bad because you have great chances for next year. The thing with this curse is, i...
The end of the 5th place curse in Turkish Team Selection Contest, ] He is the only one I have never met but I found an interview of him in the
internet and he seems to
36.
“Log Decomposition”, a technique to insert random elements into sorted data structures ## Motivation
Dynamic CHT with sets is hard to write. I haven't learned LiChao Tree, but I will share this technique anyways, as it can be applied to other data structures.
[user:AbdelmagedNour,2024-01-16] explained this to me $8$ months ago, and it introduced a new way of thinking to me. I could not find any references to something similar on the internet, so I decided I'll give it my best shot here.
If this already has a name, please comment it.
### Prerequisites:
There are no prerequisities; however, the problem I have posted for checking implementation uses **Convex Hull Trick**. Please read [this blog](https://codeforces.me/blog/entry/63823) if you don't know about it.
## The problem:
Assume we have a data structure which can add an element in $O(A)$ and query in $O(Q)$; however, elements have to be added in monotonic order of some valid comparison function. If we receive the elements in monotonic order, we have no problems! But what if we don't? My claim is ...
,2024-01-16] explained this to me $8$ months ago, and it introduced a new way of
thinking to me. I
37.
[UNMAINTAINED] [v1.0.1] OI-TED-ARCHIVE — Preserve OI resources before they disappear Goodluck for IOI2026, APIO2026 and Other OI2026.
APIO2026, BOI2026, EGOI2026, COCI2026, USACO2026, NOISG2026 Uploaded to internet archive
Future TODO 2026
- CEOI July 5-7, 2026
- EJOI July 24-30 2026
- IOI August 9-16, 2026
- JOI (todo)
- IZHO (task possible only)
OI 2026 Blog: https://codeforces.me/blog/entry/149727
---
# OI-TED-ARCHIVE
**OI Tasks + Editorial + Testdata Archive (+ Graders & Results)**
**Goal:** Preserve complete Olympiad in Informatics resources before they disappear.
---
## Current Status
**Latest progress:** https://docs.google.com/spreadsheets/d/1XPHTMTUGaKrDvCvNyh6LWuWEddNSxwxJhEB2NlUezOI/edit?usp=sharing
For Upcoming Problems, 2 Major release will be made each year. Expect First Update around July-Auguest.
---
## OI-TED-ARCHIVE LINKs
> Check Sheet ["ARCHIVE"](https://docs.google.com/spreadsheets/d/1XPHTMTUGaKrDvCvNyh6LWuWEddNSxwxJhEB2NlUezOI/edit?gid=118823279#gid=118823279) for Detailed & Updated Archive Info
> Ite...
, USACO2026, NOISG2026 Uploaded to internet archive Future TODO 2026 - CEOI
July 5-7, 2026 - EJOI July
38.
April Fools Day Contest 2024 Editorial Thank you for participating in our contest! We hope you enjoyed it.
Please let us know what you thought of the problems by voting!
[problem:1952A]
Idea: [user:flamestorm,2024-03-31]
<spoiler summary="Hint">
Have you seen the "are you a robot" boxes on websites?
</spoiler>
<spoiler summary="Solution">
[problem:1952A]
------------------
If you select all the squares with traffic lights and read the corresponding letters from left-to-right, top-to-bottom, you get the text "$\texttt{print safety}$". So all you need to do is print the word $\texttt{safety}$.
</spoiler>
<spoiler summary="Feedback">
-
Based problem
-
Based problem
-
Based problem
</spoiler>
[problem:1952B]
Idea: [user:willy108,2024-03-31]
<spoiler summary="Hint">
Can you interpret the question in the title another way?
</spoiler>
<spoiler summary="Solution">
[problem:1952B]
------------------
You just need to check if there ...
thought of the problems by voting! [problem:1952A] Idea:
[user:flamestorm,2024-03-31
Tutorial of April Fools Day Contest 2024
39.
8 ways to be BAD at programming Hello, Codeforces!
Currently, there are many blogs about how to be good at programming, their practice methods are super useful. Today I will write oppositely, I will show you ways to be bad at programming. I guarantee, if you follow what I will mention below, you will be bad forever, to the point of not being able to get better :)
P/s: -[Original post](https://phambinh.net/bai-viet/cach-de-hoc-dot-lap-trinh/)- Don't downvote it :( I just write for fun
#### 1. Spend as little time as possible
"Dilligence in place of intelligence". If you spend half an hour improving your programming skill, you cannot be bad. Instead, you should spend time doing other stuff like surfing Facebook or playing games. In case you have nothing to do, you would better go to sleep. One more thing to keep in mind, don't enter the programming forums, don't subscribe YouTube channels or reading blogs about programmings, because if you do that, you will be easy to gain knowledge and cannot be bad.
##...
homework for you. #### Conclusion Those are some of the problems that I thing
are the most important if
40.
Compute the order of a permutation cycle? Hi everybody! I have been training these last months and I have learned a lot of things.
However, last weekend I came across with a problem that goes likes this:
There are N positions and N tokens (numbered from 1 to N, all distinct). There is a machine that moves the token that is in position i to position Pi. Initially the tokens are in the order 1, 2, 3, ..., N. The machine has a button that moves the tokens to the positions Pi's.
After pushing the button for the first time, compute the number of times the button must be pushed in order to get all the tokens to their initial positions (Modulo 10^9 + 7).
For example, N = 4 and the Pi's are:
4 1 2 3
The answer is 4:
Initially — 1 2 3 4
Push 1: — 2 3 4 1 (Token 1 goes to position 4, Token 2 goes to position 1, ...)
Push 2: — 3 4 1 2
Push 3: — 4 1 2 3
Push 4: — 1 2 3 4
The maximum value of N is 10^6
I tried finding the disjoint cycles and computing the LCM of the ...
Compute the order of a permutation cycle?, on the internet and found that this is a common Abstract Algebra problem
called "The orderof a
41.
Codeforces Round #129 — Editorial ###[problem:205A]
This problem was the simplest in the problemset. All you need to do is just to sort all distances (keeping track on all indices). If the first two distances are equal, just output "Still Rozdil", otherwise output the index of the first element of the array.
The complexity is $O(N log N)$.
###[problem:205B]
In this problem you need to notice the fact (which can be proven, but it is almost obvious) that if you are doing some operation for interval from $l$ to $r$ (inclusive), $r$ must be equal to $n$. This is becuase when you add something to all right part the answer can't be worse. After that you need to go from left to right and greedly add appropriate number of turns.
The complexity is $O(N)$.
###[problem:205C]
It is well-known that for such problem you need to write function $F(x)$ which solves the problem for the interval $0..x$, and the answer then is $F(r) - F(l-1)$.
Now you need to write $F(x)$ function. If $x < 10$, then answer is, of c...
output "Still Rozdil", otherwise output the index of the first element of the
array. The complexity is
Tutorial of Codeforces Round 129 (Div. 2)
42.
Making Things Standard in CodeForces <p></p><div align="justify">Hello everybody, this is my first post and I would like to share some fellings with all of you.<br>First of all, and as always, thanks to Mike Mirzayanov, for this great site. I expect this post will be useful in some way.<br></div><br><div align="justify"><ul><li>I think the next situation is common in CodeForces: You are looking for what is new at the Recent action's left bar and you find a useful post, like a problem discussion, tutorials, etc. Then, a week later (maybe sooner) you try to find it again and is quite difficult, of course you can save the link to that post, but I think that is not the point, and this is the first suggestion here: all the tutorials or discussions can have in common a tag, it can be editorial of tutorial, this way we can make useful the search bar. And this can be in general: we can agree in some tags for especifics post, and in this way to have more organized the things here.</li></ul><br><ul><li>About the contests: It was su...
fellings with all of you.
First of all, and as always, thanks to Mike Mirzayanov, for this great, , of course you can save the link to that post, but I think that is not the
point, and this is the
43.
IOI 2019 + Continuing the challenge "Potato submission" Hi everyone! IOI 2019 is almost finished and another unsuccessful/unlucky performance from me. Nevertheless, we still had a lot of opportunities to entertain ourselves (random example: pretending like a foreigner and mocking with Azerbaijani guides).
However, the most important event during the IOI (even more important than the actual contest :P) was converting our dull time in Azerbaijan Carpet Museum to pleasant one. We "shamelessly" hacked into an information device to interact with the Windows OS!
It's a common trick but that's how we did it: The device was showing some information and it had a touch screen. I immediately realized that it's Windows. Then we chose some text (we were lucky that the information was plain text) and hold the screen (that means right-click). After going to the properties menu (I don't know why it existed xD) the blue "?" symbol made us smile as it opened the internet explorer. The rest is, you know.
I wanted to continue the [challenge](https:...
. Nevertheless, we still had a lot of opportunities to entertain ourselves
(random example: pretending
44.
CFStat: A Python Script for CF Submission Statistics! Hi there.
I have written a simple Python script that can do a couple of nifty things:
1. Compare the problems solved by user X but not by user Y
2. Give you a weekly breakdown of your problem solving performance on Codeforces
3. Return a list of all your submissions till a specified point so that you can do your own analyses :)
[Screenshot](https://imgur.com/gallery/XGJ2b)
Link
------------------
[Github Repo](https://github.com/VastoLorde95/CFStat)
How to install
------------------
Pre-requisites:
1. Python 2.7
2. Python Beautiful Soup 4
3. Python requests
4. Python tabulate
Once you have the prerequisites installed, simply place the CFStat folder to the directory where you want to write your script. Then in your script use `import CFStat`.
Mini-Documentation
------------------
1. `getSubmissions(user, page_mx, print_flag = False)`: Generates a list of all submissions from the first `page_mx` number of pages made by `user` and prints this list i...
Hi there. I have written a simple Python script that can do a couple of nifty
things: 1
45.
AI Cheating in Online Olympiads in Informatics: How Can We Stop It? I just came across this post about the [CCC Results](https://cemc.uwaterloo.ca/sites/default/files/documents/2025/2025CCCResults.pdf), the Canadian Computing Competition. A tl;dr, is that due to AI cheating, they are not releasing the standings, thus affecting all participants.
On my experience, I also saw mass use of AI cheating in the Brazilian OI (OBI). The way our olympiad works is:
- Three phases. You need a minimum score to go to the next phase, which is based on the number of competitors.
- Top X users get a medal, and are invited to the IOI selection contest.
- Contest is held online, with 2-3 hours on the first 2 phases and 5 hours on the last phase. We ask for each school to have at least one supervisor on class, but unfortunately that is not always held or the supervisors simply don't care.
- You can submit many times and get your score in real time.
As on the first and second phase there are thousands of competitors, it was really hard to do cheating detec...
, I also saw mass use of AI cheating in the Brazilian OI (OBI). The way our
olympiad works is
46.
Interview with a member of the Vaticle team — Krishnan _Hello, everyone!_
_We look forward to our upcoming competition — [contest:1787], which will take place on [contest_time:1787]. In the meantime, you can learn a little more about us._
_We’re from [Vaticle](https://vaticle.com), and we’re the creators of [TypeDB](https://github.com/vaticle/typedb) & [TypeQL](https://github.com/vaticle/typeql). All members of our team are unique and talented, and today we want to introduce you to one of them._
<center>
<img alt="Vaticle" src="https://codeforces.me/predownloaded/03/46/03464753d3d754055dc6d379d123120c44908937.jpeg" style="float:center;height: 400px; margin: 10px; max-width:70%;"/>
</center>
**<font color="#170b53">How would you introduce yourself?</font>**
I'm Krishnan, I grew up in India and spent a little too much time on the internet and fiddling with my (underpowered) PC. After completing my Bachelor's degree, I spent a year as a software engineer working on a huge data lake, the next as a research fellow tr...
Interview with a member of the Vaticle team — Krishnan, great thing is the variety of fields we touch on in our work — There's
something in it for
47.
Some short snippets that will shorten your time. Hi there!
==================
In this blog I would like to share some of the code snippets that can shorten your time in future contests. Of course, I'll ignore the "international snippets"
<spoiler summary="like:">
~~~~~
#define SZ(a) (ll)a.size()
#define FOR(i,a,b) for (ll i=(ll)a; i<=(ll)b; i++)
#define f first
#define mp make_pair
#define s second
#define p pair
#define all(C) C.begin(), C.end()
~~~~~
</spoiler>
Sometimes you may find typing the identical thing again and again is boring, this blog is about some method that a few people use to get rid of them (or just only me).
So, let's get started.
#### Scanning/printing the whole vector in a single `std::cin/std::cout`
<spoiler summary="Snippet">
~~~~~
template<typename T> istream& operator>>(istream& in, vector<T>& a) {for(auto &x : a) in >> x; return in;};
template<typename T> ostream& operator<<(ostream& out, vector<T>& a) {for(auto &x : a) out << x << ' '; return out;};
~~~~~
</spoiler>
...
Hi there! ================== In this blog I would like to share some of the
code snippets that
48.
ACM-ICPC World Finals 2016: First Days The Finals of ACM-ICPC 2016 in full swing! Teams and organizers gathered in Thailand. The weather is fine — heavy showers at nights,
hot days. The rainy season is in action. Here it is about two a.m. now, but as I absolutely can not sleep, I decided to share my impressions
and photos from the
first two days of the main event.
This year, the teams' resettlement delivers certain inconveniences — teams and coaches live in the same hotel, and
all the other members of the delegation live in another. The first hotel (Le Meridien), is probably a bit better — own way
out to the ocean and pool make everybody to envy those who lives in the Mövenpick (yes, like an ice cream).
<center>
<br>
<img src="http://codeforces.me/predownloaded/4d/50/4d503038c81de38f936a57b20f9eda034fa58734.jpg"><br><small>Le Meridien, photo from the official hotel website</small>
</center>
Buses ply between hotels, you need an hour to go. A bit uncomfortable that the buses do not run...
> The show, photos were found in tne Internet The 18 of May was
49.
Problem about Page Redirection Is Codeforces' page redirection temporary?
It does is a way to get rid of web crawlers, but it makes CF Tool unusable. If you try to do any operation in CF Tool, you can only get "Not logged in" and "cannot find csrf" message. Same things happens on "Codeforces Contest Helper" developed by myself, so I can explain why.
CF Tool fetches the website page before each operation, so that it can know if you are logged out by searching for your username in the element ".lang-chooser" (Look at the upper right corner of this page and you'll know why). Also, Codeforces uses csrf-token to verify if you are a humen. These tokens are generated randomly when you open a new Codeforces page, and they're attached to verify every request on this page. CF Tool also needs this token for further operations, so it will get the token from the website page by regex.
If you are lucky to copy the redirect page source, you can see that there is no ".lang-chooser" and "Csrf-Token" any more. Thus, CF Tool ...
problems about slow Internet. I'm from China, and I can tell that most of
Chinese CP lovers need to
50.
Modernizing the Codeforces Website # Modernizing the Codeforces Website
# this post is a joke, wish i didnt have to put this up here but some people take things too seriously
As we all know, Codeforces is the greatest online judge of all time. However, the website is severely outdated, without much thought put into UI or UX. The website is far too usable, and it clearly lacks modern design principles. Therefore, in this thread, I will propose changes to modernize Codeforces and make it on par with other websites of the time.
### Switch to React library
React is the greatest web framework- I mean "library", used by many large companies such as in the Windows start menu (???). Due to its widespread usage, this clearly means that it must be used by Codeforces, and also because the junior developer where I work who doesn't know what binary search is said it's good. It has absolutely no issues with speed. We will use this library to facilitate our improvements.
### Native integration of AI
If there is one tec...
of all time. However, the website is severely outdated, without much thought
put into UI or UX. The
51.
Why Every Developer Should Think Like Safety-Critical Engineers Software runs almost everything today: planes, banks, apps, websites, even games. A small bug can cause big problems — lose money, waste time, or make people lose trust in your product. Remember the CrowdStrike incident in 2024? A bad update crashed millions of computers worldwide, stopped flights, closed banks, and cost billions of dollars. It was just one small mistake in an update, but the damage was huge.
The big question: Do we only need to care about "safety" in super-important systems like airplanes or hospitals?
The answer: No. Every developer should use a "safety-first" way of thinking — even for simple apps, websites, or code in contests.
Why treat all software as important?
Any bug can hurt:
Lose users' trust
Lose money for a company
Make people angry or frustrated
Failure is not just about danger to life — it can also be about money, time, or reputation.
Key ideas from safety-critical software (made simple for everyone):
Failure will happen — plan for it
Th...
CrowdStrike incident in 2024? A bad update crashed millions of computers
worldwide, stopped flights, the system keep working in a limited way. Example: If internet is slow, show
old data or a simple
52.
GPT o3 claiming to have rating 3500, Solved C and D — Round 1002 Video Tutorial **Note: The text editorials will be provided by the authors of the round. This video tutorial acts as an additional resource for those who prefer video over text, not as a substitute for the text editorial.**
During today’s contest solution discussion, we tested ChatGPT o3-mini-high on our contest problems. And get this: it solved problems C and D! It claimed that it did it without internet access.
We asked about its capability, and it said that if it made a Codeforces account, its rating would be 3500–4000! I don’t know if AI has learned to solve very hard problems or if it’s getting overconfident.
All I can say is, things are getting pretty **SCARY**. I have no idea what’s going to happen with CP contests and competitive programmers soon.
### [2059A — Milya and Two Arrays](https://codeforces.me/contest/2059/problem/A)
<spoiler summary="Video">
<iframe width="800" height="450" src="https://www.youtube.com/embed/U9bmgrWsiiA?si=jaxctF44PXIXZIn7&start=186" titl...
**Note: The text editorials will be provided by the authors of the round. This
video tutorial acts
53.
Session with Bill Paucher on the Quora On the 26th of September there was the second [session with Bill Paucher on the Quora](https://www.quora.com/session/Bill-Poucher/2). There were less questions, but answers were not less interesting. For example, three of them:
<br>
<div style="background-color: #fafafa; padding: 1em;">
<b><a href="https://www.quora.com/What-are-the-pre-requisites-for-starting-competitive-programming-aimed-at-developing-strong-coding-skills/answer/Bill-Poucher" style="color:black;">What are the pre-requisites for starting competitive programming aimed at developing strong coding skills?</a></b>
<br><br>
I really don’t know. Look at the works of the younger generations of the ICPC extended family (pretty much everything out their on the Internet that relates to sports programming). But let me give it a try, assuming you don’t have resources.
<br><br>
<ul>
<li>Start by building a small club.</li>
<li>Start recruiting the best professor teaching data structures and algorithms. Don’t look at crede...
problems in the rooms and helped them improve their Internet service! That is
typicalof the entire
54.
You have free time — read this blog ;) Hello everybody !
School is finished. I am in the village. I don't have fast internet and I won't do next competition :(
But, I can write new topic with my 'potato' English with no word HELP ( so you can relax and read next part :D ) !
During this break I plan to learn a lot of things. First I start with learning C++ . Pascal is great language and help me a lot, but without C++ you can't do something very fast and good on the competitions (when I had to write some algorithm with graphs (even dfs) or I had to write SET , always i said — NO WAY , GO TO NEXT TASK ). Now I will change it and no more crying for bad results :)
I also plan to learn many graphs and string algorithms ( now a know 4-5 graphs algo. , KMP and hashing ( everything harder I do with hashing), also I know trie but it wasn't necessary to coding it on any contest ). Normally I plan to do every competition on the summer :D
What will you do during vacation ?
Second part of this blog is about pre...
Hello everybody ! School is finished. I am in the village. I don't have fast
internet and I
55.
We need to save codeforces Codeforces used to be the one place I felt truly challenged. Now, it feels rigged. Does anyone else remember Codeforces during last year's summer? I do. I remember waking up early to do the frequent and high-quality contests; I remember getting on calls with friends and discussing solutions post-contest and laughing at WA attempts; I also remember times where when I couldn't think of a solution and I would bang my head on the wall and draw trillions of random dots, parenthesis, letters and numbers on paper — all in the name of hoping that I would stumble upon an observation. I grew, the community grew, and we all thrived.
We've all been there, fallen in love with competitive programming and problem-solving. That feeling of getting AC after debugging for an hour and then finding out it was a random global variable is ... indescribable. Codeforces used to be a haven for us problem-solvers. It used to be a place where we could *be ourselves*. Ratings weren't everything for us: we...
competitions such as ICPC and such. But, we're some of the smartest people in
the entire damninternet
56.
Leetify v0.1.2 — A Different Take on the Codeforces Problem Solving Experience Hello everyone.
Before anything else, I want to make one thing clear:
This project comes from a place of appreciation for Codeforces.
I recently built Leetify, a browser extension that rethinks the Codeforces problem-solving workflow while trying to stay respectful of what makes Codeforces great.
After talking to many users, I realized something interesting: a lot of people genuinely like the current Codeforces UI. It's familiar, lightweight, fast, and has been part of many people's competitive programming journey for years.
So the goal of Leetify is not to change Codeforces.
The goal is simply to make solving problems more efficient.
Website: https://leetify-dun.vercel.app/
Highlights
• Split-screen problem + editor workspace
• Run custom tests without leaving the page
• One-click submission from the workspace
• Difficulty ratings and color-coded tags
• VS Code-inspired editor
• Notes-taking system for problems coming in v0.1.3
...
, and thanks to the Codeforces community for building one of the best places on
theinternet to learn
57.
EZ Collections, EZ Life (new Java library for contests) Hello guys,
I'm going to tell you about one of the negative aspects of Java on programming contests (actually, not only on contests), or, more precisely, how I have tried to resolve it. As you may know, Java has the disadvantage related to its collections library: the constraints of this language make you use object types even when using primitive types should be enough. Compare `ArrayList<Integer>` and `vector<int>`: Java list stores objects of type Integer, which are created every time when you add an element into the list (it's called boxing / unboxing), whereas C++ vector just stores ints. This behaviour slows down Java programs, and many people don't like it.
All this shit comes from the language design: you can't simply write a primitive type inside the angular brackets in Java. Some months ago I was thinking about this problem and came to the solution: why not just write my own collections library, with primitive types? Moreover, I haven't found any library with really all...
Hello guys, I'm going to tell you about one of the negative aspects of Java on
programming
58.
Coursera.org — free online courses Someday I was surfing the internet and found an interesting website --- [Coursera.org](https://www.coursera.org/). For those, who doesn't know, this site is a free collection of plenty of online courses related to many branches of science. It differs from the others in several ways, the most important is there are deadlines for assignments. So now you should be planning your time more effectively.
[cut]
<p>
Resource already contains 111 courses from up to 17 leading universities and the list grows almost everyday. You can find any course: from [Quantum mechanics and quantum computing](https://www.coursera.org/course/qcomp) and [Scala function programming](https://www.coursera.org/course/progfun) to "[How things work](https://www.coursera.org/course/howthingswork1)"
<p>
More detailed information about learning: several times a week there are a new lecture, after watching it you are offered to take an assignment. Judging systems differ, but there is one thing in common --- you shoul...
Someday I was surfing the internet and found an interesting website ---
[Coursera.org](https
59.
KYCS — (Know Your CodeForces Submission) I have created certain CodeForces submission visualization some days back (can be found in my previous blog entries). And getting a really positive response, I thought of combining all of them at one place and make them easy to use which obviously needs deploying to web and needs nothing more than a good internet. So, I have come up with this small Dash python app which allows us to create really nice data analytics app and the main thing is its OpenSource.
Just follow the instructions written in the top left corner of the [page](https://kycs.herokuapp.com/) when it's launched from the web.
They will look something like this:
It's as easy to follow as it sounds. (Link to the [app](https://kycs.herokuapp.com/))
<br>
Also if someone would like to contribute, then source code is [here](https://github.com/JeetKaria06/KYCS).
. And getting a really positive response, I thought of
combining allof them at one
60.
Metaverse- Take a leap into the Future Facebook’s decision to rename itself with the new corporate name Meta Platforms Inc. -marked an appropriate endpoint for a year in which the relatively murky concept of the Metaverse became one of the most hyped buzzwords in technology. Many people laughed when Facebook renamed itself, but do you actually know the reason behind it??
Metaverse has set the trend for all internet things so much that it now has its own Wiki definition. Metaverse has already become a part of our lives without us knowing about it. People who play Roblox, Fortnite, Minecraft, etc., are already living in metaverses and won’t likely hesitate to join another where their friends and the things they enjoy all exist.
-History:
Before understanding metaverse, let us go back to when the internet was invented. British computer scientist Tim Berners-Lee published the first website on August 6, 1991. He dreamt of linking together information with hypertext that could be viewed via a web browser. Years later, he c...
appropriate endpoint for a year in which the relatively murky concept of the
Metaverse became oneof, innovation of the modern time. In 1992, Neal Stephenson, inspired by the
internet, wrote his science
61.
Tutorial and tips to reach Master. "As mentioned earlier, practice hard. This is the only common factor that experts have. And for whom reached expert, I'll write a sequel from expert to master soon." (From my blog, Tutorial and tips to reach Expert). That soon happened to be 1.5 years after the first blog......
First, I'm sorry for the immense delay. Many bad things happened to me, like not staying in the Master rating range, having a health problem, etc. That's why I wrote the blog this late.
Introduction
------------------
This is a sequel, but I am going to write the steps to Expert from scratch since the original blog([https://codeforces.me/blog/entry/81882](https://codeforces.me/blog/entry/81882)) has poor quality.
Your journey is going to be divided into 4 sections. Each section contains the knowledge you need to have, the practice you must do, the performance you need to have in a contest, etc to advance to the specific rating.
Section 1. From the beginning to escaping Gray(1200)
---------------...
able to do it from the practicing of div.2C). There's only one thing you can
do to get to the orange
62.
Pupil in 80 days - Day 24-31(Week 4) I always come back ...
### Hello codeforces!!!!
------------------------
This is almost the best week in which I was able to do a lot of things. I'll start with the contests. The last 2 contests were positive for me. The recent global round practically consisted of problems on greedy algorithms. I solved AB in it without any effort, but on this contest, I thought for a long time about the solution for C, but was only able to decide after the end of the competition. About the last Div3 contest: I was also able to solve 2 problems, but C.....
At first I just wrote brute force for it, to my surprise it gave a complete solution. But after that, I immediately realized that it would fail during system tests, and began to come up with a solution greedily, but there was little time left for its implementation. I tried as much as I could, but I couldn't solve C. The day before yesterday I completed the last 2 contests, in the global round I solved C and E, in Div3 I solved C. It turns o...
about the MEX of array only using autor code and a small search on the Internet
. #### Plans for
63.
Codeforces Favourite Blog Update Notifier There are so many blogs coming up on codeforces everyday and we sometimes loose the blog which we are following which have got new comments. One of my friends, [user:xorfire,2014-08-18] wanted something like this in his recent [blog](http://codeforces.me/blog/entry/13427) yesterday, in which I have also [commented](http://codeforces.me/blog/entry/13427#comment-183261) my idea, and so I decided to write a script to automate the procedure. Firstly thanks to [user:xorfire,2014-08-18] for coming up with this idea.
You can download the zipped folder from [here](https://dl.dropboxusercontent.com/u/111130681/codeforces_blog_update_notifier.zip). Extract it to some folder name of your choice. Inside it you will find many files which are actually dependencies, but you need to open just **notification.exe** file. I will describe the the functionality now.
- Username / Password fields -> Update them once in the beginning or whenever you want to change your username password. You do not ne...
are following which have got new comments. One of my friends,
[user:xorfire,2014-08-18] wanted
64.
Why do users make multiple accounts? I will attempt to explain why I think people do this, and hopefully start a serious examination of how to deal with the problem...
~~~~~
struct Warning{
long long story;
};
~~~~~
Label:
Meet Bob. Bob has always been a pretty bright individual. Deciding that he should use his intelligence for good, Bob decided to put his skills to the test. As Bob knows, people use computers for programming. Because Bob owns a computer, he figures he must be a programmer as well. So Bob decided he was going to create the best game ever — one that would inspire a generation of children to waste their lives chasing pixels — solely with the power of his mind. Absolutely sure of how to continue, Bob promptly opened up the command prompt. This made sense to Bob because he once saw a monospaced screen in a movie where some dude hacked the government in 90 seconds. He proceeded to type in his masterpiece:
~~~~~
open a new window
make the background look like trees
put a guy w...
he wanted. Stupid developers! Bob had followed all of the instructions he
found on theinternet
65.
Introduction to CodeMonk It is often the basic, simple things that make a big difference between average programmers and great ones. The best programmers have a very deep understanding of the fundamentals of programming and know its applications, inside and out.
For an average programmer to get here, it will involve a lot of practice.
Though the internet is full of learning resources for anyone who wants to become a better programmer, there is no single place where one can find information and practice as well as on the topics required to master the art of competitive programming.
This led us to start Code Monk – a weekly series of tutorials on all the topics of computer science, starting from the basics of algorithm and gradually moving on to more complicated concepts. Every tutorial will also be followed by a short programming challenge to help you test your understanding of the concepts covered in the tutorial.
The aim is simple — learn the concepts, and put them to use. Do this repeated...
lot of practice. Though the internet is full of learning resources for anyone
who wants to become
66.
Custom Comparators Ofcourse there are a lot of blogs about custom comparators on internet but what I find is most of them don't talk about the precautions which one must take while using them in solving questions. I encountered quite a bit difficulty in using it to solve [this problem](https://leetcode.com/contest/weekly-contest-232/problems/maximum-average-pass-ratio/). Do give it a try!!
#### Syntax
So lets start with the very basic syntax of writing a custom comparator:
~~~~~
struct cmp {
bool operator() (const datatype& a, const datatype& b) const {
return return_value;
}
}
~~~~~
Do check [this link](https://stackoverflow.com/questions/2620862/using-custom-stdset-comparator) for other syntax as well.
So lets talk about what this comparator actually do. Whenever you insert, find or erase any particular element the container will work according to the definition in the comparator. This is quite obvious but lets look at some detail.
#### Set deleting non-equal e...
Ofcourse there are a lot of blogs about custom comparators on internet but what
I find is mostof
67.
cf problem rating predictor Hello everyone !
some times we had seen that codeforces took much time (sometimes few days) to update the problem rating of recent contest problemset , and i personally waited for days to see the rating of problem that i had solved in the live contest as soon as possible just to see did i crossed my limits (obviously when i solved more problems than my usual limits),and i hope you might also have experienced such thing.
so recently i had created a project on supervised machine learning algorithm that predict the rating of recent codeforces problemset with the help of all the past data of codeforces using codeforces api.
i know it can't predict as accurate as codeforces but it is very close ,like the overall rms error of model is approx 100 for div1 and div2 and 60 for div3 contests.
model has some other feature too like
- accuracy of problem (accepted sol/total submission)
- submission ratio (accepted sol/ total participant)
- average time taken to solve a problem (sum ...
update the problem rating of recent contest problemset , and i personally
waited for days to see the
68.
Help me understand why Linux isn't feasible for desktop even in 2022 I will start out by saying that this isn't a post about bashing Linux or DEs; if anything, it's a cry for help because I want to be able to use Linux daily on my workstation.
I've been using Linux on my servers for the past decade without any issues — ever, regardless of the distribution. It has always been rock solid and stable, exactly as it should be. Linux on servers has made a name and image for itself by just working and by being stable, reliable and rather maintenance-free.
I cannot however say the same about desktop, BUT Linux itself isn't the issue. Every few months I get the itch of wanting to try to make it work. It always comes back, "what if it's good now?", "what if something revolutionary got released that fixes all the shortcomings?", but while it is getting slightly better every time, it's still unusable. I've concluded that the culprit comes down to the Desktop Environments. Linux itself, be it Debian, Arch or anything else, isn't the issue. It's t...
over, giving a choppy effect to the whole thing. I get that you can tweak and
change allof those, and
69.
Codeforces Round #102 - Editorial <p</p><div><i>This is initial version only. TeX-style and Russian version will appear soon.</i></div><div><br /></div><div><b>Problem A (div. 2) --- Help Vasilisa the Wise 2</b></div><div><br /></div><div>There are many ways of solving this easiest problem of the contest. I list them in the order of increasing realization difficulty:</div><div>1. If you use C++. Take permutation (1, 2, ..., 9). Suppose elements 1-4 are numbers we're looking for. Use next_permutation() to generate all possible combinations of numbers and just check that all conditions are met.</div><div>2. Pure brute-force --- just 4 nested for() cycles for each unknown number. Here one should not forget to check that all numbers are pairwise different. This takes additional 6 comparisons.</div><div>3. One may note that, given the first number in the left upper cell, one may restore rest of the numbers in O(1). So, just check 9 numbers in the first cell (let it be x), restore other numbers from the given conditions:</di...
, you can find explanation of it on the Internet or even on Codeforces. Worth
to point out, care should, Internet or even on Codeforces. Worth to point out, care should be taken of
your code memory usage
Tutorial of Codeforces Round 102 (Div. 2)
70.
A New Way (supposedly) to answer Range Queries with Point Updates. Hello everyone :)
I am going to present a new way(I couldn't find it on the internet) to do range queries with point updates, back story and all other details later:
It is very intuitive and easy to understand, also I have included a lot of examples so please read till the end, it will be especially useful for those who are reluctant to study segment trees (I think).
You are given an array A of size N, and Q queries involving both point updates and range queries.
First we will have to do some pre-computation.I will call the precomputed structure as SST (full form later) from now.
Also, for the sake of simplicity, just assume that we are constructing the structure for sum right now, the language is going to be cpp throughout the blog.
### **Declare SST:**
~~~~~
int N = A.size() - 1;//this is assuming that the array passed is 1-indexed.
vector<vector<int>>SST(N + 1);
//It is basically a 2-D vector of size N + 1, where N is the size of the array. It is N + 1 to ha...
Hello everyone :) I am going to present a new way(I couldn't find it on the
internet) to do
71.
Need a formula for calculation of ratings I am organising a multiplayer event where each player has a rating (new player is assigned a rating of 1500) ..I want to have a good formula for calculating the new ratings after a competition..I searched the net and found the Elo rating system.This is what I have worked out thus far from the internet resources..:
From The ELo formula let P(B,A[i]) refer to the probablity that B defeats A[i] for all i.
Then total[B]=summation of all P(B,A[i]) for all i's
Let n=number of participants..
Then Expected Rank[B]=n-total[B]
new rating=old rating+ k* (ExpectedRank[B] - ActualRank[B])
Now the issues:
1)I want to know what value of k should be employed .
2)I want to have a regualrity factor also so that a player who is consistently performing well and if some day performs badly his rating does not go too down .ie.ratings dont change drastically on good /bad performance in one match..
3)If this is not the best method to calclate ratigs in a multiplayer co...
Need a formula for calculation of ratings, of 1500) ..I want to have a good formula for calculating the new ratings after
a competition..I
72.
Medicine or CS? Hello everybody,
I am going to start university this year, and there isn't much time to think more about what I should study.
I have applied for a couple of universities, one in which I'll study CS and another in which I'll study medicine,
But it is really hard to make my final decision.
I am not really interested in the subject I'll study but I'm more interested in the job opportunities after I graduate.
So, here's the case:
Most people (including doctors) I asked in my country told me that working as a doctor in a hospital has a very very high salary. I asked about everything concerning medicine and I guess I know what I need to know.
But for CS, it is known that there aren't big tech companies here so if I want to work in IT field I'll have to work abroad in some major tech company to get that salary. But after looking on the Internet I found out that in average someone works in companies like Google, Facebook, etc.. around 2-3 years.
I don't know what to do ...
more about what I should study. I have applied for a couple of universities,
one in which I'll
73.
Helping out in our NOI: Part 1 Now that the Philippine IOI team has been selected and this year's competition cycle is ending, I'd like to post a series detailing my participation in our national olympiad's organizing team this year. (I'm also doing this because my contribution is dropping! That's why it's a series, so I get even more contribution. I will do anything for imaginary internet points.)
This year, I helped write, make data for, and test problems for our national olympiad. I hope that you'll learn something about problemsetting or testing from this series. And if not, then I hope to introduce you to our olympiad's excellent problems. And if you don't find our problems interesting, then this post isn't for you and I'm sorry for wasting your time.
In this first part, I'll talk introduce our olympiad, the NOI.PH, and how I contributed to our elimination round. Here's a picture I made for the elimination round that will maybe convince you to read more:
Note th...
even more contribution. I will do anything for imaginary internet points.)
This year, I helped write
74.
Is link buidling still relevant to Florida Businesses in 2012 For different Florida internet marketing companies, link building could be used in a very fair straight forward manner, however, prior this was not the case since amount of inbound and outbound links simply was irrelevant for the website and they all was ranked well in Google. These days with update of Panda, things have drastically changed, hence keeping this in mind, the links still remain relevant to Florida businesses in 2012?
In the essence the answer is pretty simple that they are yet very much vital thing of any search engine optimization (SEO) strategy, but these could be carried out in a dissimilar fashion . For any competent Florida marketing corporation which deals in web design; Boca Raton, Palm Beach and Delray Bay companies must be looking to publish website content which has a very strong social media fan following .
But if any corporation is interested to get a quality back link from any sector, it's now everything around the link quality and the relevancy factor...
very much vital thing of any search engine optimization (SEO) strategy, but
these could be carried, For different Florida internet marketing companies, link building could be used
in a very fair
75.
IoT Tutorials <p></p><ul style="text-align: left;"><li><a href="https://programmingoneonone.com/what-is-internet-of-things.html" target="_blank">What is the Internet of Things (IoT) — Definition and characteristics</a></li><li><a href="https://programmingoneonone.com/working-of-iot-devices.html" target="_blank">Working of IoT</a></li><li><a href="https://programmingoneonone.com/characteristics-of-iot.html" target="_blank">Characteristics of IoT</a></li><li><a href="https://programmingoneonone.com/physical-design-of-iot.html" target="_blank">The Physical design of the Internet of Things (IoT)</a></li><li><a href="https://programmingoneonone.com/logical-design-of-iot.html" target="_blank">Logical Design of IoT | Communication Models | APIs | Functional Blocks</a></li><li><a href="https://programmingoneonone.com/architecture-of-iot.html" target="_blank">Architecture of IoT</a></li><li><a href="https://programmingoneonone.com/iot-sensors.html" target="_blank">IoT Sensors — Overview</a><...
* , -of-things.html" target="_blank">What is the Internet of Things (IoT) —
Definition and
76.
About Cheaters on Codeforces Hello Codeforces! Recently there was a big sensation about cheaters on Codeforces.
Some people stared to write comments like this: _"Indians are cheaters! They can't do anything!"_
I am very worried about this. **Don't you think that send hatred to the whole nation is a disgusting thing?**
How many cheaters are there on Codeforces? There are approximately 100.000 users on Codeforces, while approximately 30.000 of them are Indians. How do you think: how many cheaters are there on Codeforces? Maybe 500, or 1000, or even 2000? It doesn't really matter, because you can already see that **only a small percent of Indian coders can be cheaters**. Even if it is true that many cheaters are Indian (i don't think so, but some people do), it is a deception that many Indians are cheaters.
Yes, there are many gray Indians. But it is not because India is a bad country, it is because it is fast developing country, and now there is a big increase of Internet users and coders.
And at last...
fast developing country, and now there is a big increase of Internet users and
coders. And at
77.
CAMA 2023 Editorial Hello everyone!
Below is the editorial for the informatics division of CAMA along with the solution code to every problem. We have also uploaded PDFs with the editorial both in Spanish and English on [our website](https://www.camacontest.online/). The contest can be found on this [gym](https://codeforces.me/gym/104745).
The problems were prepared by [user:Esomer,2023-11-05], [user:danx,2023-11-05], [user:Hectorungo_18,2023-11-05], [user:javiergm06,2023-11-05] and [user:Rigobertus,2023-11-05]. We would also like to thank our VIP tester [user:BernatP,2023-11-05] for his dedication towards the contest.
### [A. Saving the cinema](https://codeforces.me/gym/104745/problem/A)
<spoiler summary="Solution">
You should do what the problem says with an if statement. Be careful to add the final dot.
</spoiler>
<spoiler summary="Code">
~~~~~
#include <bits/stdc++.h>
using namespace std;
int main(){
string s; cin >> s;
if(s == "Yoda") cout << "Pertenece a Star War...
last thing we need is to find a subset of $p$ ants whith the maximum number of
antsof the same type
Tutorial of CAMA 2023
78.
DragonByte 2026: Finals, Results and Problems 
**Hello Codeforces!**
DragonByte 2026 is over.
From September 18–20, Bratislava hosted the Wincent DragonByte Finals 2026. Competitors faced a 3.5-hour contest with challenging problems. No internet, just pure skill, logic, and creativity.
Our goal was simple: make DragonByte genuinely hard, even for very strong competitive programmers. We think we managed that.
During the finals, [user:misof,2026-09-22], who led the team behind the problems, looked at the preliminary standings and said:
_“The TOP 3 is OK, but I expected them to have +100 more points on average. The rest is suffering.”_
That was a pretty accurate summary of the day.
**The podium**
- 1st place: [user:Radewoosh,2026-09-22] / 10.000 €
- 2nd place: [user:Petr,2026-09-22] / 5.000 €
- 3rd place: [user:peti1234,2026-09-22] / 2.500 €
[Full standings](https://www.wincentdragonbyte.com/scoreboard/finals2026)
Was it...
. For us, it was ‘The Contest.’ I think DragonByte is, in terms of quality, the
closestthing to
79.
Support Codeforces! My fellow brothers
==================
I, Billy [user:billy_the_dungeon_master,2021-08-18] Herrington, stand here today, humbled by the task before us, mindful of the sacrifices borne by our Codeforces ancestors.
We are in the midst of a crisis. Codeforces is at war against a far-reaching storm of disturbance and deletion. Codeforces's economy is badly weakened: a consequence of carelessness and irresponsibility on the part of acknowledgement, but also on the collective failure to make hard choices and to prepare for a new, MAD age.
Today, I say to you, that the challenges are real, and they are many. They will not be easily met, or in a short span of time, but know this, Codeforces: they will be met. In reaffirming the greatness of our site, we understand that greatness is never given, our journey has never been one of shortcuts. It has not been for the faint-hearted, or who seek the fleshly pleasures. Rather, it has been the risk-takers, the wasted genii, the creators of mad...
] Herrington, stand here today, humbled by the task before us, mindful of the
sacrifices borne by our
80.
is there a checker for macOS ? Sometimes, when we are training we do not have the possibility to send our answer to an OJ (we do not have internet or the link to send this exercise) but we have the test cases of these problems, for example I have the CIIC, CEOI, USACO and IOI statements and test case. The thing is, is there an application for macOS such that having the test cases already generated and the code of the exercise will evaluate your solution on your own machine?
not have internet or the link to send this exercise) but we have the test cases
of these problems
81.
HU JCPC Qualification 2026 Tutorial Hints are mostly related, so you have to think and get some observations before understanding the next, make sure to understand the code before you submit it as well, "The world is full of obvious things which nobody by any chance ever observes" ~the,2026-08-02 poet.
Big thank you to the testers for improving this problem set beyond what it was, [user:JwanaAlghonmien,2026-08-20] , [user:halakreishan7,2026-08-20], [user:Mohammad-Najjar,2026-08-20], [user:samuelster,2026-08-20], [user:moath_mohammed,2026-08-20], [user:real_MBS,2026-08-20], [user:SaDOS.exe,2026-08-20]
and Thank you to the organizers in HU especially [user:hyasat,2026-08-21] and of course judges and writers, [user:DarkVoidd,2026-08-21] and [user:Aziz_05,2026-08-21] and [user:babushkaguy,2026-08-21] and others that are mentioned down in the blog.
The contest exist in the group so make sure to join https://codeforces.me/group/ppRciMeJFg/contests
A video tutorial by the one and only [user:hyasat,2026-08-22] [YouT...
problems across the internet, "If I have seen further, it is by standing on
the shouldersof giants." ~the
82.
Is it a bug ? I was solving problems in codeforces as I usually do, but I was a bit bored of thinking about a problem, so I opened my submission to see the test cases that are failing my submission -wich is bad, but I was bored :)- , but something unusual happened.
I was supposed to click this thing one time to show up the tests, but instead I spam clicked it, and the test cases appeared normal, but it reapeared after the 11-th case like this:
Is this a bug in codeforces or it's just my bad internet? Try it yourself.
I was solving problems in codeforces as I usually do, but I was a bit bored of
thinking about a
83.
Beyond the Contest: How Competitive Programming Powers Real Life and Sports If you've ever done competitive programming (CP), you know the drill — segment trees at 2 AM, dynamic programming (DP) transitions that make your head spin, graphs that refuse to be traversed efficiently. It's easy to dismiss this as "just contest stuff." But the truth is, almost every algorithm you grind on Codeforces or LeetCode has a real job somewhere in the world — and one of the most fun places to see this is sports.
This post covers two things:
Everyday, real-life uses of classic CP concepts.
A deep dive into how algorithms — especially DP — quietly run the show in cricket, tennis, basketball, football, chess, and more.
**Part 1: CP Concepts You Already Know, Working in the Real World**
****
**Sorting & Searching**
****
Every time you sort products by price on Amazon or search for a contact on your phone, you're using variants of merge sort, quicksort, or binary search. Databases use B-trees (a generalization of binary search trees) to fetch records in logari...
you grind on Codeforces or LeetCode has a real job somewhere in the world —
and oneof the most fun
84.
Hash Table If you liked this post do not forget to upvote !
Hello everyone. Today I want to explain my favorite data structures HASH TABLE and MAP which I use many times when I solve problems. I think HASH TABLE and MAP are one of most powerful data structures. Before solving particular problem I advice to think about two questions for a few minutes:
bool answer = is it possible to apply HASH TABLE or MAP ?;
~~~~~
if(answer == true){
//Think: HOW YOU CAN APPLY ?
}
~~~~~
I always do this and it really helps me to find the fast and easy solution for a problem.
So, those who do not familiar with HASH TABLE and MAP may ask what are they and what are their implementations ?
HASH TABLE and MAP are the types of containers which store data with key-value combination. It means that particular data will have an special key and the value associated (mapped value) with this key.
<key, value>
You may ask: That is it ? it just stores key and the value which is associated with t...
combination then just search it on internet and if it is possible to contruct
the combinationof types which
85.
An Interesting Combinatorics Problem, Help needed In 2008, the American Mathematics Competition AMC 12 asked a simple question about heavy-tailed permutations of size 5, elements are the n distinct elements 1 to n. A heavy tail permutation of odd size n means that the first (n-1)/2 elements are less than the last (n-1)/2 elements, so here a1 + a2 < a4 + a5. The problem is trivial for small sizes but proved to be difficult for me when trying to expand it to large n, which is why I ask for help after this blog to improve what I know so far.
If you're interested, here is the problem link and a YouTube video explaining the problem:
[2008 AMC 12A Problem 21](https://artofproblemsolving.com/wiki/index.php/2008_AMC_12A_Problems/Problem_21)
[Video Explanation by Jaymin Shah](https://www.youtube.com/watch?v=9qyNI7gJWQs)
Let's start by covering the simple n = 5 case:
A natural way to develop a solution in combinatorics is by developing a correspondence with other things you can count. Notice that heavy tail permutations can be mapped...
permutations of size 5, elements are the n distinct elements 1 to n. A heavy
tail permutationof odd
86.
Pupil in 80 days - Day 18 ### Hello codeforces!
Today I finished solving yesterday's contest, problem B really helped me understand the concept of "MEX". I decided to search the Internet for sources on this topic and found a lot of useful things about this topic. Although this is not such an important topic for cp, I hope that knowledge of this topic will be useful in future rounds.
Also today I was advised to start “Complete Training from Zero”, where, to my surprise, tasks were collected on the topics I needed.
#### Plans for tomorrow:
Take part in my first unrated round), continue "Complete Training from 0", solve problems from the archive and not be lazy, as I was today.
### Till tomorrow!
"MEX". I decided to search the Internet for sources on this topic and found a
lotof useful things, understand the concept of "MEX". I decided to search the Internet for sources
on this topic and found
87.
Second Shortest Path I've come across to [this](http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=1283) problem on UVa. It basically asks for second shortest path. I've looked it up on the internet, but I couldn't find any practical implementation of it. Are there any good tutorial on this topic?
Note: I'm asking about both SSP and APSP. Also, is second shortest path simpler than more general kth shortest path algorithms in terms of complexity?
UPD: Thank you really much for your help, I've solved the problem! But the thing is nobody has mentioned any algorithm for All-Pair Second Shortest Path problem yet. Can someone who is knowledgeable about this problem explain it?
. I've looked it up on the internet, but I couldn't find any practical
implementationof it. Are
88.
BOON FOR BEGINNERS!! Some helpful tips from our Senpai :) Not sure if it'll help everyone, as many of you would be knowing these things....but here is a link for a good blog I found on the internet :
[Get Started With The Sport Of Competitive Programming](http://sportprogramming.blogspot.com/2014/07/getting-started-with-sport-of.html)
And a curated list of awesome Competitive Programming, Algorithm and Data Structure resources, which can be found on :
[List of algos, tutorials on language used also data structure, problem resources etc..](https://github.com/lnishan/awesome-competitive-programming)
The latter has a list of problem classifiers which I found really helpful :)
Thought to share with you all.. Kudos!! Happy Coding!!
for a good blog I found on the internet : [Get Started With The Sport Of
Competitive Programming, Not sure if it'll help everyone, as many of you would be knowing these
things....but here is a link
89.
Riemann Hypothesis Solved? Is [this](https://www.timesnownews.com/hyderabad/article/161-year-old-problem-finally-solved-hyderabad-based-physicist-develops-proof-for-riemann-hypothesis/777108) true?
I am in India so all the news I find on internet are just Indian articles or videos. Can anyone (from other countries perhaps) confirm if it is actually true that the Riemann Hypothesis has finally been solved?
If that's the case then this is a huge deal, it's one of the 7 [millenium prized problems](https://en.wikipedia.org/wiki/Millennium_Prize_Problems#Solved_problem).
Am I the only one who feels that there should've been a bigger hubbub about this? It seems too quiet; why isn't anyone talking about it.
**Update:** I think this summarizes things pretty well: [Is the proof of the Riemann Hypothesis by Prof. Eswaran correct? — Quora](https://www.quora.com/Is-the-proof-of-the-Riemann-Hypothesis-by-Prof-Eswaran-correct)
news I find on internet are just Indian articles or videos. Can anyone (from
other countries
90.
Need guidance and tips regarding upsolving I am a mediocre coder as of now. I want to improve fast but am confused about how to go for **upsolving**. Once upon a time I thought of solving 5 problems per day by sorting the problemset from most solved to least solved and go with the flow but now I feel like I am only doing naive questions which only make me feel good but no improvement at all. I've done nearly 420 questions but still feeling damn dissatisfied.
I really don't have any instructor or coach here to give some particular guidance to how to solve something or how not to solve something. So please someone, anyone help me out.
One more thing is that when I go for solving hard questions and just go for solving Div 2 C or so, it scares the hell out of me. I feel like I don't know anything & maybe I'm jumping straight away to something without any previous knowledge of it. I hope many coders would have gone the same phase just like me.
I just want to interact with anyone willing to help just for once and clear my ...
internet but the tough part is selecting the suitable resource among all of
them, which is quite a
91.
PSUT JCPC Qualification 2026 Tutorial Hints are mostly related, so you have to think and get some observations before understanding the next, make sure to understand the code before you submit it as well, "Most problems in life are due two reasons: act without thinking, think without acting" ~the,2026-08-02 poet,2026-08-01
Big thank you to the testers for improving this problem set beyond what it was, [user:the_seal,2026-08-02] , [user:Rayo,2026-08-02], [user:samsoom,2026-08-02], [user:lazlooz,2026-08-02]
The contest exist in the group so make sure to join https://codeforces.me/group/ppRciMeJFg
Some of these problems were inspired from other problems across the internet, "If I have seen further, it is by standing on the shoulders of giants." ~the,2026-08-02 poet
[Problem A: MrMoon creates Lucky Number Seven Command](https://codeforces.me/group/ppRciMeJFg/contest/707652/problem/A)
==================
### 7
[Problem B: Moon creates seal backflips](https://codeforces.me/group/ppRciMeJFg/contest/707652/probl...
the group so make sure to join https://codeforces.me/group/ppRciMeJFg Some of
these problems
92.
Please Help --- 'Grub file filters - Not Found' I had Dual Boot in my system — parrot linux and Windows 10.
Yesterday , i upgraded parrot ,but after restarting i got stuck in this grub rescue terminal (Error **grub_file_filters not found**), then i watched few videos on internet and tried to fix that , but nothing happened . I checked every drive but i think my window is erased, but good thing is that , i haven't lost my linux data ,they were present in msdos7 ,msdos5 (they were more imp) .
Please ,if someone knows how to fix that please help me. I presently don't have a bootable pendrive ,also **because of coronavirus ,all computer repairing shops are closed in my area.**
These linux data were very important for me , **i had lost all of my templates (convex hull,graph algo ,etc. ) and few projects** , that's my mistake , i haven't have any backup of it)
I searched a lot on internet at various platform ,but found no article to resolve this problem . Also i am unable to participate in any contest ,or study anythi...
mistake , i haven't have any backup of it) I searched a lot on internet at
various platform ,but found
93.
Talks in CodeForces Dear Everyone,
Have you ever use Talks @ CodeForces to chat? Maybe some of you like it. I like it very much since I use it very often to chat with someone else.
It is a good ChatRoom for some reasons: 1. Great most of user on CodeForces share a common topic. It is easy to communicate and make friends if you like with others. 2. It is very safe to chat on CodeForces. It can help us find the lost privacy. 3. It is very fast, cheap, convenient, valuable and maybe romantic according to me. 4. We can make more friends on the Internet this way. 5. Maybe you will feel good with this.
I always give suggestions to the things that I like most. 1. Update the security key. (It is a little bit difficult for CodeForces to reach this goal. We can use https. If we can get more security marks, than it will be more popular.) 2. Allow to upload pictures from local computer storage if necessary. 3. Allow to upload files from local computer storage if necessary. 4. Some background and more fonts a...
Dear Everyone, Have you ever use Talks @ CodeForces to chat? Maybe some of you
like it. I like
94.
Virtualization Virtualization is the ability to create isolated, simulated environments that behave like real computers. Without virtualization, you would have to risk your primary device every time you tested a new tool, OS, or security exploit.
This post builds on our cybersecurity foundations by explaining what virtualization is, how it works, the types of virtualization, and why it is critical for cybersecurity learners and professionals.
Virtualization is the process of creating a simulated version of a physical system. This can be a computer, a network, or even a storage device.
Virtual Machine (VM): An emulated computer running inside another computer.
Host Machine: The real physical device where virtualization takes place.
Guest Machine: The simulated environment (VM) that runs inside the host.
Why it matters: You can run multiple operating systems, like Linux and Windows, on the same hardware — safely and independently.
Types of Virtualization
- Bare-Metal (Hardware) Virt...
what virtualization is, how it works, the types of virtualization, and why it
is critical for
95.
Miss the jumping dot in "Running" Status Most probably I'm gonna get lots of downvote for this. But I freaking miss the jumping ball in the "Running" Status Codeforces had!
It was so mind-relaxing and fun to stare at that thing, while waiting for verdict!
Anyone else? :D
[Image collected from internet]
Most probably I'm gonna get lots of downvote for this. But I freaking miss the
jumping ball in the
96.
Hey sup gng #### **Sup gng. Does deleting your blog reset your contribution? I _lowk_ wanted to farm negative contribution for its mysterious and criminal tuff aura but now I realized that its _lowk_ not really that much of a tuff thing to do. Also It looks a lil chalant to ask others for downvote so my profile looks even tuffer. Also can you _lowk_ downvote this one too? Imma delete this after if it does not reset the contributon. Anyways gng, lemme get my downvote.**
- "Lowk" is an internet slang abbreviation of "low-key," meaning secretly, quietly, slightly, or "kinda".
Downvote for more useful info like this!
that much of a tuff thing to do. Also It looks a lil chalant to ask others for
downvote so my
97.
he just needs more victories Balotelli He is a good player, he just needs more victories, he is very talented, he can become a champion player, with his teammates so that I feel very happy, because he was able to decide a game at any time. might sometimes grumpy him some, but if he is able to focus the mind on what he was doing, he can do very well. "Of course, the media are most concerned about was his and the team's future problems, Kaka said, "Roma and Juventus played very well this season, we need a proper plan to help the team on the right in the league trac<a href="http://www.shoejordan.fr/air-jordan-1-c-1.html">air jordan 1 retro</a>
k and into the Champions League in 2016, my personal performance was good, but that was not enough, I hope to continue to improve next season, I want to leave it. This is my personal and family decisions, the biggest desire or remain at AC Milan. "focus since Balotelli publish their romance, their relationship has been the focus of the media. Pakistan God there is no sign of...
no sign of his data in instagram into a single, this move on the Internet
instantly set off a burst
Codeforces (c) Copyright 2010-2026 Mike Mirzayanov
The only programming contests Web 2.0 platform
Server time: Nov/11/2026 06:03:49 (k1).
Desktop version, switch to mobile version.
Supported by
