(though it is admittedly hard to tell) that barely gets talked about:
self-deception. Self-deception, very hard problems. I still did the virtual contests like before and from the
outside, it may seem
→ Pay attention
→ Top rated
| # | User | Rating |
|---|---|---|
| 1 | Benq | 3857 |
| 2 | jiangly | 3810 |
| 3 | maroonrk | 3534 |
| 4 | tourist | 3528 |
| 5 | Kevin114514 | 3510 |
| 6 | turmax | 3411 |
| 7 | Um_nik | 3387 |
| 8 | Radewoosh | 3367 |
| 9 | heuristica | 3322 |
| 10 | strapple | 3317 |
→ Top contributors
| # | User | Contrib. |
|---|---|---|
| 1 | Qingyu | 158 |
| 2 | maspy | 150 |
| 3 | Um_nik | 146 |
| 4 | Errichto | 139 |
| 5 | adamant | 136 |
| 5 | nik_exists | 136 |
| 7 | maroonrk | 134 |
| 8 | DNR | 133 |
| 9 | Dominater069 | 131 |
| 9 | AmShZ | 131 |
→ 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.
Self-deception: maybe why you're still grey after practicing every day I generally don't like to give much advice on "how to practice", but recently I have been thinking a lot about this and I realized that there is something that I believe affects a lot of people (though it is admittedly hard to tell) that barely gets talked about: self-deception.
Self-deception is a devious thing. It can be very hard to detect, yet can be fatal to improvement.
This blog is mainly directed to greys, greens and cyans that can't get out of these categories. Most examples are given with that in mind. That being said, I believe others have something to think about as well.
This is my first blog on such "psychological issues" and I don't know if I'll ever make another one. It's certainly a difficult topic to write about because for most of the blog, the message is "your practice is not as good as you think it is" or even "you aren't as good as you think you are" which can of course be a hard thing to hear. Thus, I have to somehow be very gentle while getting the poin...
2.
Pro Tips - get them while they are free More tips to use while studying under my tutoring [here](https://um-nik.notion.site/Pro-Tips-8b923b0dc7c94770824bdf4184afc43c).
## Stop caring about the rating
Unless there are prizes involved, your position in the standings makes no difference. I can feel awful after winning a contest if I know that I could solve one more problem. Or I can feel OK losing a bunch of rating points knowing that I solved everything I could. Because rating is just a number. It is highly volatile and it depends on other people, not only on your skill. But solving problems is totally up to you. And you should evaluate yourself not based on some random metric, but on your honest feeling whether you performed up to your expectations. Your sense of self should be under your control, don't get hung up on some imaginary value, you cannot reduce your progress to a single number.
## Don't use more than one account
Rating is just a number. Do not be afraid to lose your colour. You’ll get it back in no t...
problem? as a play on some standard problem? as a special case of some hard
(NP-complete maybe) problem
3.
The Reason You are Bad at Codeforces — You are Not Russian Enough If you are triggered by this clickbaity blog title, you are probably interested in improving your Codeforces skills. Now, I will share my point of view on the differences between Codeforces and ICPC contests, and how you can, in my humble opinion, maximize your Codeforces rating gain.
I mostly consider that all conceivable competitive programming problems need three aspects of skill:
1. Observation — the ability to understand the problem and come up with non-trivial properties.
2. Technique — the ability to apply a well-known algorithm or data structure to the problem.
3. Implementation — the ability to code fast and debug fast.
Collaterally, I refer to these three skills as Russian-ness, Chinese-ness and American-ness, respectively, for reasons you will soon see below.
## Observation (Russian-ness)
Observation means that you stare at some problem for a sufficient amount of time and you are able to reduce it to some easier problem. One good proble...
engage with. Now we get the intuition why it is so hard to improve at
Codeforces: you are trying sohard
4.
If you ask me how to improve your algorithm competition skill, I will give you the link of this blog. In recent one year, I don't know why but there are many people sending messages to me for asking similar problems. So I decide to create this blog.
In the beginning, I must say, you may feel disappointed after reading this blog. Because I don't have any special tips. My study method has wasted me many many time.
There are some basic points I think you have known.
1. **Practice, practice, and practice.**
I take so many time to think and solve problems. I think I do it 5 hours a day on average.
2. **Make friends with many awesome people.**
I know many awesome people. For example, [user:arosusti,2015-02-24], [user:kelvin,2015-02-24], peter50216([user:0O0o00OO0Oo0o0Oo,2015-02-24]), [user:seanwu,2015-02-24], [user:Shik,2015-02-24], [user:takaramono,2015-02-24], [user:tmt514,2015-02-24], ...
If I have some problems that I can't solve in few weeks, I can almost get solution from my friends.
Then I say what I do for training myself.
When I do problems. There are two possi...
disappointed after reading this blog. Because I don't have any special tips. My
study method has wasted
5.
My Story, Thoughts and Motivation Hello Codeforces! Over the weekend I attended the British Informatics Olympiad final. Today I'd like to share my CP journey so far, some thoughts on how it was, and my plans going forward.
I started programming in general when I was 12; I learned JavaScript from an old book that was lying around in my house and wrote some small websites — as a lot do when starting out — and generally dabbled in whatever interested me.
Through the COVID lockdown I played multiplayer video games with some school friends such as Minecraft, and played various JRPGs with my sister such as Tales of Symphonia. I took a hiatus from programming but towards the end of the lockdown and as in-person school began to start, I decided to pick it back up again.
In April of 2021, I signed up to [Codewars](https://www.codewars.com/users/myst-6). I wouldn't describe this website as a competitive programming — problems feel less math-y and (usually) don't require complex algorithms but instead f...
I begun — how I would study long and hard, spending lots of time solving
problems on Codewars
6.
How to train: why it's not enough to just do a lot of tasks Hello, Codeforces! I, like many of you, read blogs periodically. Lately, blogs from low-rated users who ask me how to raise their ratings have been catching my attention. I want to tell you a little bit about my opinion on these blogs.
So what do these blogs look like? Usually this is a blog with a title something like <b>"I need help right now!"</b> or <b>"How to improve my rating, help me!"</b> When you open this blog, you see the most detailed description of the problem, such as: "I have solved 500 problems, but no improvement" or "I have solved 100 problems with rating >= 1500, but my rating is not increasing". And in the comments they usually write "you haven't solved enough, solve more" or "solve more difficult problems". <b>In my opinion, this is incorrect and misleads such users.
So, imagine that you do not know anything at all about sports programming, or even about the basics of Olympic math. You at best (because many people don't even do that) have learned a programmin...
that hard, if you reason logically. As I see it, it is harder to show that for
an unsorted array
7.
My sad story When I was submitting the problem D in round #371, I clicked the "Choose File" button and selected my code.
Before the submission, I read my code another time, found a bug in my code and fixed it. And then I clicked the "submit" button.
But it turned out that my solution got wrong answer on pretest 4. I stress-tested my solution, and found it passed the big random data. I was really shocked. umm... Maybe my solution failed on some small testcases. So I tried many ways to generate testcases. But my solution was right on all the testcases I generated.
After struggling for about 40mins, I gave up and submitted it again. It passed all the pretests.
I compared two codes, and just found I submitted the old version (before fixing the bug) at first time.
After asking my roommate, he said when you clicked the "Choose File" button, it would upload the file instead of recording the path.
In the rest time of the contest, I tried to solve problem B and E but failed.
<S>I think ...
I should quit from algorithm contest like [user:WJMZBMR,2016-09-13] and study
harder., I think I should quit from algorithm contest like [user:WJMZBMR,2016-09-13] and
study harder.
8.
[Educational] Combinatorics Study Notes (1) Hello Codeforces!
Today I'll be writing about what I have learnt about combinatorics, which played, and, in my opinion, will still be playing a important role in both Codeforces and CP (short for competitive programming).
However, combinatorics is such a great subject that made that impossible for me to write it all in one blog. So, this is just the very first blog, which is for beginners. If you are interested, please, pay attention to this account and I'll give posts as series for a long term.
If you have found some mistakes in the text, or if you have some questions about the topic, please, leave a comment, and I'll check it weekly and reply. Also, if you find some grammar mistakes, a kind comment will be also welcomed.
### Thanks
- [user:happyivan,2022-12-21], [user:Ptilon,2022-12-22], [user:ck1ne,2022-12-22] for pointing out some problems in the text.
- [user:kill_all_placeholder,2022-12-21], [user:hydracody,2022-12-22] for providing possible topics.
### Content...
[Educational] Combinatorics Study Notes (1), without the implementation, it's hard to write, and complain the time
complexity out. In the, , because without the implementation, it's hard to write, and complain the time
complexity out., Hard to count directly? If it is hard to solve "Sets choosing numbers
9.
I reached master (+ what practice strategies don't work) I've just hit my goal of reaching yellow on Codeforces. Thus, I'm celebrating by sharing with everyone what I've learned over the years while trying to improve.
I've done _a lot_ of research on my own when I was at a lower rating, constantly googling and looking at blogs to try to come up with the "optimal practice strategy", and failed every time. So, I think my experience in failing is going to be very valuable to a lot of people reading this.
Let's imagine a very simplified case of what happens when we're doing a problem. When solving a practice problem, these combinations of things can happen:
1. Solve? Yes/No
2. Tried a lot of ideas? Yes/No
3. Used the editorial? Yes/No
Now, here are the simplified rules I follow to tell if I'm improving or not.
- If you did not solve, did not try a lot of ideas, and did not use the editorial: you did not improve.
- If you did not solve, did not try a lot of ideas, and did use the editorial: you did not improve.
- If you did not...
ideas. You didn't improve. Now, how about problems that are too hard? You try
maybe one or two ideas, . You didn't improve. Now, how about problems that are too hard? You try maybe
one or two ideas, get
10.
Rewarding hack points based on problem scores Currently, any successful hacks on any problem provide exactly 100 points. For problem A and B it seems quite reasonable, but I find it barely motivating to lock harder problems and try to hack (unless it's known that the pretests are exceptionally weak), since:
- You risk losing a lot of points on system test. Even if you realize mistakes in your code after lock, you can't do anything.
- There are (usually) not many solutions to look into in your room in the first place.
- Harder problems (usually) require hard techniques and longer implementation, so reading each solution takes a lot of time.
- Even if you successfully hack, 100 points don't affect your rank too much.
Rewarding more points for hacking solutions for harder problems would make the system more interesting and balanced. My suggestion is to reward 1/10 of the problem's score for successful hacks. i.e. 50 points for hacking a solution of a 500-point problem, and 200 points for hacking a 2000-point problem.
Here...
(usually) require hard techniques and longer implementation, so reading each
solution takes a lot, - Hacking solutions of a hard problem requires you to understand the hard
problem itself, high
11.
EPIC Institute of Technology Round Summer 2025 (Codeforces Round 1036, Div. 1 + Div. 2) # Hello Codeforces Once Again
<img alt="" src="https://codeforces.me/predownloaded/4e/71/4e713a365fc86888c808b3b56d6fecfb529973e6.png" style="float:right; height: 154px; padding-left: 35px; padding-right: 73px; padding-top: 41px; padding-bottom: 33px;"/>
After months of hard work, [user:cry,2025-07-01], [user:Lilypad,2025-07-01] and I are extremely proud to welcome you to participate in [contest:2124] at [contest_time:2124]. This round is combined for Division 1 and Division 2, and it will be rated for everyone.
You will be given $3$ hours to solve $9$ problems. One problem will be split into two subtasks.
We would like to thank the following people for making the contest possible:
- [user:satyam343,2025-07-01] for outstanding coordination, working tirelessly with us to improve problem quality and donating his own problems to us. I cannot thank him enough.
- [user:Error_Yuan,2025-07-01] for proposing some ideas that weren't used in the end.
- [user:Benq,2025-07-01...
; padding-right: 73px; padding-top: 41px; padding-bottom: 33px;"/> After months
ofhard work
12.
[Educational] Binary Search Study Notes (1) **Hello Codeforces!**
Binary search is useful in many situations. For example, interactive problems or minimizing the maximum problems. Binary search is a good choice when dealing with many situations, and for many binary search problems, monotonousness may be hard to find out and participants may not be able to focus on binary search.
You may think that binary search is simple, but after this blog, you may think more about how binary search is working on competitive programming.
### **Part A** — What is binary search?
Consider the following problem: you are going to guess a number between $0$ and $100$, and I'll tell you that the number you give is smaller than the number I thought about or not. How to minimize the number of your guessing?
Well, you may guess $50$ first, if $50$ is too large, guess $25$, otherwise $75$, and so on. For each guess, you cut off half the possible numbers, since $x$ is small, the numbers smaller than $x$ are also small. If $x$ is large...
[Educational] Binary Search Study Notes (1), search problems, monotonousness may be hard to find out and participants may
not be able to focus, situations, and for many binary search problems, monotonousness may be hard to
find out and participants
13.
The inevitable despair of a fallen man, a truly demotivating rezil story Hello CodeForces, tonight we mourn the sad demise of a man who once was a legend, truly an icon in the Turkish CP community. That man is [user:AhmetKaan,2025-09-21] Avcı. Let me tell you the sad, disgusting story of how he became who he is and what has yet to happen to him.
Our story begins in 2004, just two days ago in September 19th. Born in Kastamonu/Türkiye to a family of 6 children, a family that posseses one IMO participant (Ömer Avcı), and one older brother who once dominated Turkish Olympiad programming. ([user:farukkastamonuda,2025-09-21] orz) This man was obviously blessed with inspiration from an abundance of role models inside his own home. Even though genetics seemed to be to his advantage, he always lacked the skill to even do simple math. He cried his nights yearning to become like his elite brothers. It just didn't come natural to him, ever.
His prayers were answered and his older brother Faruk came back home from his highschool outside Konya, and trained him al...
contests although he feels like he is training hard. He was even spotted
listening to https, study for the ridiculously competitive memorisation based Turkish university
admission exam system
14.
On "is this greedy or DP", forcing and rubber bands #### Introduction
When it comes to "problem-solving techniques", there are roughly 3 levels:
1. Concrete algorithms (Kruskal's algorithm, Li-Chao tree, fast Fourier transform)
2. General patterns (dynamic programming, greedy, square-root decomposition)
3. Meta-strategies ("how do I even go about solving this problem?")
There is some grey area, but in general this classification works well.
[Many tutorials](https://codeforces.me/catalog) have been written about ideas that fall into 1 or 2.
But very little has been written about the third category. On the catalog, I think the
only blogs that really qualify are [this](62730) and [this](20548). There is also
[this](92248?#comment-809401) valuable comment. As to why there is so little written,
I think I can identify two reasons.
- Most strong contestants don't really consciously think about these.
After solving a problem with FFT, it's hard not to know you used FFT.
If you used DP, even if you did it without thinki...
problem with FFT, it's hard not to know you used FFT. If you used DP, even if
you did it without
15.
[Educational] DSU Study Notes (1) Hello Codeforces!
Data Structure is a legendary subject that it's really hard for me write it down completely in a single blog, so let's discuss simple DSU first.
DSU is really easy for beginners to understand. Also, this blog talks about more than the simplest DSU.
**UPD 2023-1-19:** Time complexity analysis updated, thanks [user:Everule,2023-01-19] for help.
### **Part 0** — How does DSU works?
Firstly, DSU is short for "Disjoint Set Union". Let's go to a simple task then.
> There are $n$ elements, the $i$-th element is in the $i$-th set initially, and now you can do $m$ queries below:
> — `M a b`, to merge the set that $a$ belongs to and the set that $b$ belongs to into a new set. If $a$ and $b$'ve been in a set already, then do nothing.
> — `Q a b`, to tell if $a$ and $b$ are in the same set.
Let's go straight to the problem solution.
**Solution：**
Let's consider contructing a graph. Initially we have self-cycles for all vertecies, whi...
[Educational] DSU Study Notes (1), Data Structure is a legendary subject that it's really hard for me write it
down completely in a, Hello Codeforces! Data Structure is a legendary subject that it's really hard
for me write it, The proof is using potential energy analysis which may be too hard to
understand for beginners. In
16.
How not to perform well on life(With how not to perform well on ICPC bonus) First of all, for a long time I wanted to write this blog but I keep delaying it and finally here I am. After seeing [user:matthew99,2017-08-23]'s blog I decided to my time has come. I really wanted to write like him but my English skills aren't enough to use "you would" dozens of times. So I will explain how I didn't perform well in my life, and if you do same things you will end up succeed at failing in your life.
And it's very important to say at this point, I'm very bad at English, so if you're disgusted you can stop right there and I'm truly sorry about it.
**TLDR** : I am a loser.
I was a regular student before high school. I interested with math olympiads little bit but I didn't get even a national medal just a several contests. By the way I won a The New iPad. So I am passing that times and coming to high school.
In our country national eliminations goes like that, paper based elimination at may, national OI at december, team selection contest at march/april. High s...
have no chance. But [user:muratt,2017-08-25] intended to study for it and he
was at a lower grade, ] was a god so I though I have no chance. But [user:muratt,2017-08-25] intended
tostudy for it and he
17.
How not to perform well on Team Selection Contest x2 I read these blogs ([user:ErdemKirez,2019-05-01]'s [blog](https://codeforces.me/blog/entry/54007) , [user:matthew99,2019-05-01]'s [blog](https://codeforces.me/blog/entry/53624) and [user:I_love_Hoang_Yen,2019-05-01]'s [blog](https://codeforces.me/blog/entry/54064) ) and decided to write my story. Maybe it's becoming boring but there is no other place to share my feeling.
**9th Grade**
I joined the olympiad class at my school. And that year I studied math, basic C and some algorithms. Because in Turkey First round of the national contest consists of these topics. I did well on that, Probably I would be able to participate the Second round but as you know from the [user:ErdemKirez,2019-05-01]'s [blog](https://codeforces.me/blog/entry/54007) Coup d'état attempt happened and all of these rounds canceled. And also my school was closed the by government.
**10th Grade**
I went to another school. TUBITAK (Organizer of National Contests) did not announce for a long time for the ...
previous school it was hard to study olympiad. At this year I studied hard and
won a silver medal in, I changed my school again because at my previous school it was hard to study
olympiad. At this year, In Turkey, there is an exam for university selection called YKS. It really
needs tostudy for
18.
[Educational] Combinatorics Study Notes (4) Hello Codeforces!
Today I'll be writing about what I have learnt about combinatorics, which played, and, in my opinion, will still be playing an important role in both Codeforces and CP (short for competitive programming).
However, combinatorics is such a great subject that made that impossible for me to write it all in one blog. So, this is just the **fourth** blog, which is friendly to beginners. If you are interested, please, pay attention to this account and I'll give posts as series for a long term.
If you have found some mistakes in the text, or if you have some questions about the topic, please, leave a comment, and I'll check it weekly and reply. Also, if you find some grammar mistakes, a kind comment will be also welcomed.
### Previous Blogs
- [Combinatorics (1)](https://codeforces.me/blog/entry/110376), basics.
- [Combinatorics (2)](https://codeforces.me/blog/entry/110390), implementations.
- [Combinatorics (3)](https://codeforces.me/blog/entry/110799), ar...
[Educational] Combinatorics Study Notes (4), $ be the set of unlabeled ones. Unlabeled Graphs are hard to count, count
labeled graphs. Let $g$ be, Unlabeled Graphs are hard to count, count labeled graphs. Let $g$ be a graph in
$G$. Then the, With the 2 problems discussed above, then it's not hard to get that
$\sum_{i}^{\infty} C_{i+k-1}^{k
19.
MNM Cheating Algorithm MNM algo
==================
Once upon a time, three Syrian competitive programmers decided to spend their time in doing research and studies. they worked hard.
Finally, hard work paid off and they discovered the algorithm -which Codeforces uses to catch cheaters [the ones who violate Codeforces contest rules]. Their lives have just become easier and now they can copy codes from each other / Ideone without spending time changing variables names and methods declarations order.
Those three inventors are [user:Math_Master,2018-02-24], [user:NourAlhadi,2018-02-24], [user:Mr.spring,2018-02-24]. (hats off people ...).
MNM -(first letters of [user:Math_Master,2018-02-24], [user:NourAlhadi,2018-02-24], [user:Mr.spring,2018-02-24] respectively)- Cheating Algorithm is -in my opinion, the greatest since the invention of breadth/depth-first search algorithms.
MNM is simple, here is a simple explanation for it:
------------------
- MNM relies on "divide and conquer" approach in solvi...
research and studies. they worked hard. Finally, hard work paid off and they
discovered the algorithm, spend their time in doing research and studies. they worked hard. Finally, hard
work paid off and
20.
[Reserach] The application of ML techniques on certain problems (i.e. How to make crazy hard problems that nobody can solve) Background
==================
The idea of this article originated from a contest (Petrozavodsk Summer-2016. Petr Mitrichev Contest 14), which I believe is attributed to [user:Petr,2018-07-25]. In this contest, an interesting problem is proposed:
"Cosider this process: pick a random number $n_i$ uniformly at random between $10$ and $100$. Generate $n_i$ random points with integer coordinates, picking each coordinate independently and uniformly at random from all integers between $0$ and $10^9$, inclusive. Find the convex hull of those points.
Now you are given $10000$ polygons generated by this program. For each polygon, you need to guess the value
$n_i$ that was used for generating it.
Your answer will be accepted if the average (over all $10000$ hulls) absolute difference between the natural
logarithm of your guess and the natural logarithm of the true $n_i$ is below $0.2$."
Unfortunately, I didn't really manage to work this one out during our 5-hour training session. ...
[Reserach] The application of ML techniques on certain problems (i.e. How to
make crazyhard
21.
Introduction of Neowise Labs Hello, Codeforces!
I’m excited to introduce to you Neowise Labs. We’re going to host an upcoming [contest:2096] and have prepared presents for you. Neowise Labs was founded by Max ([user:dark_ai,2025-04-11]), Igor ([user:Igor_Kudryashov,2025-04-11]) and me, and here is our story.
<center>
<img style="width:400px;" src="/predownloaded/16/41/16415eb2b19a656db6f7e133296434dea3391a21.jpg"/>
</center>
[user:Igor_Kudryashov,2025-04-11] and I have been in the same ACM ICPC team for many years while studying at the Saratov State University. [user:dark_ai,2025-04-11] was in the Saint Petersburg State University team so we were competitors back then :) Those years in the university we were doing the same as all other competitive programmers: solve problems, make contests, practice, practice and practice again (and sometimes study). I’ve even enjoyed being a Codeforces platform developer in my final year of study.
[cut]
<center style="margin-top:30px;">
<img style="width:450...
, practice and practice again (and sometimes study). I’ve even enjoyed being a
Codeforces platform
22.
Strange Situation about IOI eligibility Hello,
I have dual citizenship (Taiwan and USA), and I currently study in an American high school located in Taiwan. I've already participated in the regional contest about 7 weeks ago and did pretty well, so I qualified for the national contest.
So now I'm practicing as much as I can for the national contest, but recently I was told that I could qualify for the training camp but not the national team for Taiwan.
I searched online for IOI rules and found this link on the IOI-2017 site: http://www.ioinformatics.org/rules/reg17.pdf. Here are some parts of it that stood out:
"A Contestant is a student who was enrolled in a school at a level not higher than secondary education, in the Country they are representing, for the majority of the period 1 September to 31 December in the year before IOI’n. Students who are studying abroad may represent the Country of their nationality."
Not only am I studying in Taiwan, I also have Taiwan citizenship, so I definitely fit this criteri...
Hello, I have dual citizenship (Taiwan and USA), and I currently study in an
American high
23.
Farewell, Kuroni... <spoiler summary="Always remember, never forget">
<a href="https://imgflip.com/i/5e8bnd"><img src="https://i.imgflip.com/5e8bnd.jpg" title="made at imgflip.com"/></a><div><a href="https://imgflip.com/memegenerator"></a></div>
</spoiler>
Erm, so...
Today for me starts like any other day, I woke up, ate breakfast, and visited Codeforces for fun. To be honest I didn't compete in any contests for a while, as I have a lot of exams and studying online.
I'm pretty bored so I scrolled down randomly, and I found something that hit me, like a truck.
One of the highest-rated and most respected Codeforces users in my country, [user:Kuroni,2021-06-23], left the Codeforces community.
I checked his profile, and he left it with nothing but a blank in his profile picture, and a line below his nickname that says "Goodbye". That's it, nothing else.
I was completely shocked. I even cried for around half an hour. I mean, anyone that has a big contribution to this community (and high-r...
hard for me to come through, life must continue. But for now, I will sit back
and take this as a
24.
How to read problem statements But [user:Um_nik,2018-10-26], we all know how to read, we have our whooping 2 month of experience! Oh, my sweet summer child, my experiments show that many people with kinda cool achievements like medals on ROI don't know how to read statements. But don't worry, I'll teach you. Well, probably you won't understand anything, because you didn't try to understand anything in your life, you expect all hard work to be done for you by someone else. Let's start!
Basic rules
==================
- The result of reading the statement is usually pure math model. If story helps to build correct understanding, you can keep it, but still try to discard as many unnecessary details as possible.
- Imagine you want to tell the problem to someone else. What parts you want to tell? (According to my PM, this rule won't help you).
- Shorter = better.
- Simpler = better.
- Limitations are part of problem statement. Especially small limitations, because for small data you can try all the possib...
hard work to be done for you by someone else. Let's start! Basic rules
25.
Girlfriend vs Tree I was walking with my girlfriend, having a great time, when suddenly I saw her yes, that Tree.
She caught my eye and stole my heart. I thought, who cares about my girlfriend? Something much more important had just appeared.
I left my girlfriend and hurried after her, not even knowing who she was
Someone nearby announced, as if it were the most important news
That’s the Tree.
I went up to get to know her. She looked at me, cool as ice, and said, You need to know the Tree topics
Of course I forgot my girlfriend, forgot everything, and started studying hard, as if the world were ending
After a huge effort, I came back to her, heart pounding, and said, I did it!
Then she gave me a Tree problem to see if I truly deserved her.
I tried — and failed — and suddenly realized I had lost everything: no Tree, no girlfriend.
Now I’m standing here, laughing at myself, realizing life sometimes forces you to study Trees more than love… and more than anything else.
And yes —...
Of course I forgot my girlfriend, forgot everything, and started studying hard
, as if the world, Of course I forgot my girlfriend, forgot everything, and started studying hard,
as if the world
26.
LI2 Contests Announcement — Free Programming Course Hi everyone!
I'm thrilled to invite you to the **LI2 Contest — free collection of high-quality contests to master every topic** — here, on Codeforces! [Group Link! Click here!](https://codeforces.me/group/jtU6D2hVEi/blog)
### Current avialibale list of topics:
Loops; Prefix Sums; Sortings; Binary Search; Recursion; Sweepline; Two Pointers; Linear Data Structers (stack, queue, etc); Graphs, DFS, BFS; Dynamic Programming; DSU; Shortest Paths; Minimum Spanning Tree; Greedy; ...
### Why this course?
I believe that finding high-quality problems is the hardest part of practice, especially when you are only getting your feet wet with competitive programming.
There are many lectures and articles, but not so many open collections of problems for each topic.
### Time-tested
I guarantee you that this course is time-tested, **I used it myself**.
LI2 is short for Boarding Lyceum №2 in Kazan — the school I study in. So we've been using this course for...
short for Boarding Lyceum №2 in Kazan — the school I study in. So we've been
using this course
27.
[Testing] Gray testing Hello, CodeForces!
I am Cristofor Zaharescu. I am a teacher, in the Liceul Tehnologic Alunis. I was rather intrigued about the fact that not so many newbies get to examinate certain problems rounds, which in my eyes if quite a foolish thing for the future of the CodeForces community. I feel like normalizing Newbies test in rounds will succeed in the following things:
- Boosting self confidence. Knowing you are important, and the fact that you can contribute in rounds, is something that can really upper your mettle in resolving wordproblems, making it easier to improve and having a higher chance to perform fairly well in future contests, as well as lowering the likelihood of giving up on programming competitively.
- Experience. The fact that people get to test problems early on is quite meaningful, due to the fact that, when the Newbies will improve, go up a couple of colours, and need to test harder problems, the feedback they will give is going to be more appropriate, ...
for beginers, yet that require some strategies one wouldn't know at that
level. Astudy has shown, quite easy for beginers, yet that require some strategies one wouldn't know at
that level. Astudy has
28.
Proof for Modular Division trick This short video serves as proof for the following mathematical statement:
<br>
$$
\displaystyle \textbf{(H)} : \frac{a}{b} \mod m = a \cdot b^{-1} \mod m
$$
$$
\displaystyle \text{Such that } b \mid a \text{ and} \gcd(b, m) = 1
$$
<iframe allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen="" frameborder="0" height="500" referrerpolicy="strict-origin-when-cross-origin" src="https://www.youtube.com/embed/BMDUYcgt1A8" title="YouTube video player" width="850"></iframe>
<br>
[problem:1999F] urged me to study modular arithmetic, specifically modular division. However, no document or video I found contained this proof, so I tried to prove it myself. It's not hard, so maybe that's why I couldn't find it, or maybe I didn't search well enough.
Anyway, often we are tasked with calculating a large number modulo $10^9 + 7$. For this, we need to perform some modular arithmetic tricks, but things get complica...
[problem:1999F] urged me to study modular arithmetic, specifically modular
division. However, /BMDUYcgt1A8" title="YouTube video player" width="850">
[problem:1999F] urged me to study
29.
Anyone can set problems, and so can You So yeah, hey guys. I'm [user:aryansanghi,2025-06-22], the "cyan author", the "trash problemsetter", the "author of [contest:2120]". So, you might be wondering, who am I to suggest anything to you? Well, I don't know, you clicked on the blog. I have made sections, you can just skip to what you want to read.
Brief History of Me
==================
First of all, I'll give a brief history of myself, because why not? You might not be expecting it, but problem-setting is my passion. I've been setting problems on Physics and Maths during my JEE time. If you are interested, you can find them [here in drive](https://drive.google.com/drive/folders/1UT9cvcx1KMmjFDHNEb5EFwuwT7i49BIg?usp=drive_link). I had ~100 more in [brilliant.org](brilliant.org), but sadly, the community feature was disabled around July 2021. If you are interested, I can get it exported and share it with you. After coming to IIT Kharagpur, I joined CodeClub and set some problems in the unrated CodeNite that we conduct hal...
half yearly, along with amazing peers, some hard, some easy, you can find them
[here in doc](https
30.
Kindly share your Experience — last regional ACM contest — what's next ? Hello CF community...
2 days ago, It was my last regional contest (ECPC). for the last 5 years, I was training for the ACM while studying (like most of us) and help the other newcomers in the problem-solving community. In the last ECPC, one of the students who I was training had really bad luck in the contest and spent too much time on one easy problem and didn't solve it! I think most of us have experienced this. anyway, After the contest, she said I have no reason to continue the training! I did my best last year and didn't get any good results! and I even don't know what's the benefits of problem-solving in a practical job after leaving competitive programming! (we all will leave these competitions one day, whatever the reason) she was really disappointed. I know that feeling and I reach a mental breakdown 2 years ago (still trying to recover).
competitions -like anything in life- have advantages and disadvantages, you may work very hard and things go wrong! you got WA instead...
life- have advantages and disadvantages, you may work very hard and things go
wrong! you got WA, - and what would you say to anyone worked very hard but didn't get any good
place and feel
31.
R.I.P HajAgha Hello to the sad world without HajAgha..
It's been about a few weeks, let me start from the beginning.
His real name is "AmirReza" but we call him HajAgha because of his faith.
He was my best friend and we started studying Olympiad together.
He was the best one from the beginning and he was solving problems way faster than us.
He was very kind and he would always help weaker students. such as [user:Sam86_b,2023-11-16], he was the weakest last year but now with HajAgha's help, he is better than us.
His dream was always participating in IOI and every day he was trying hard to reach that dream, he reached expert pretty fast but something unexpected happened. He was fighting a disease, but he couldn't survive it.
His death has been really hard for us. after that, we were disappointed and lost, but now we want to start stronger with his memory.
Our Olympiad group: [user:wop,2023-11-16], [user:A20221218,2023-11-16], [user:Ramtin510,2023-11-16], [user:mehrad22,2023-11-16], [user...
better than us. His dream was always participating in IOI and every day he was
tryinghard to reach
32.
Some thoughts Hi, my name is Paiva, I'm 17 years old and I live in Brazil. Last week, we had the Brazilian Team Selection Test for IOI, and I got 6th place. I spend all this year studying for this test, and I really thought that I would go to IOI this year, but I was defeated. I should be thinking about how I lost a great opportunity for my life, right? I should feel sad, right? In fact, I could not be happier.
I started doing Olympiads in my 7th grade (2019), with mathematics Olympiads, and since then, I had a dream to go to IMO, and since then I spent almost all of my time studying for make this dream come true, but I never thought if I was enjoying what I was doing. After some time, I wasn't liking what I was doing, it fell just like an obligation, but I could not stop, because I thought that if I dropped it, I wouldn't find something worth fighting for.
It was in 2021 that I started learning about competitive programming, and I really fell in love with it. It had everything that I liked in...
about 2 years just studying for it, and I thought that all this time that I
study would be for nothing
33.
Intuition or Motivation Behind Alien's DP Trick Although this post is directed at people who are already familiar with Alien's Trick, if you are interested in learning about it, it is based off [this IOI 2016 problem](http://www.ioinformatics.org/locations/ioi16/contest/day2/aliens.pdf), and the method of solving the problem is described [here](http://www.ioinformatics.org/locations/ioi16/contest/IOI2016_analysis.pdf).
I am currently studying some common DP optimization tricks such as CHT (Convex Hull Trick) or Knuth's Optimization. When I got to Alien's Trick, however, it was much harder for me to wrap my head around it. I am able to follow the math and understand the reasoning behind it, but I just cannot seem to build intuition or see how someone would go about coming up with this trick on their own. Although, I know [user:j_______________________,2018-06-29], for example, was able to get full points on the problem during the contest.
I know that [user:j_______________________,2018-06-29] and whoever came up with the proble...
34.
How to become Master. I see a lot of newbies trying to get better at cp.
But working hard isn't enough.
You need to have a goal in mind and follow it till the end
(like becoming X till Y).
Here I am gonna give some tips on how to become master.
#### Participate in contests
For master you need rating.
To get rating you have to participate in contests.
Nothing more needed to be said.
#### Solve problems
To get a good place in a contest, you have to solve problems. So, obviously, try to solve as many problems as you can. You might say that me saying this is useless and idiotic, but I disagree! I see a lot of people that give up after solving a certain amount of problems, but don't be like those people. They will never achieve anything meaningful in life.
#### Have the correct mindset.
Competitive programming is just as much about programming as it is about having a good mindset. It's all about competing, so you have to be in the right state of mind. You might ask me what it is, but I can'...
fancy, you may want to study Rudy's Trick (Rudy's trick is not a DP
optimization but it is an, I see a lot of newbies trying to get better at cp. But working hard isn't
enough. You need to
35.
Ten years of competitive programming 2 Hey Codeforces!
I’m AmirReza PourAkhavan, Codeforces Contest Coordinator. I let the story become complete and I’m sharing it now.
The story is about a 16-year competitive programmer, who left his family and migrated to another city alone to follow competitive programming. After seven years, he advanced to the International Collegiate Programming Contest World Finals, twice.
Read the previous post [here](https://codeforces.me/blog/entry/107465).
10th grade
===
Trying alone
------------------
In my tenth grade, the situation got worse. Before that, at least, I had some colleagues and at least a class per two weeks. But in the new grade, these brights disappeared too. Still, I was trying to do it alone. I remember when I learned the Dijkstra shortest-path algorithm and implemented it for the first time, how happy I was.
Suddenly, my rating growth started. As you can see, my rating in Oct ‘14 was 1057 (minimum rating) and In Feb ‘15 I achieved 1761. Those years, >= ...
located). I went there to study, but there was a problem. Sometimes, we played
games, and sometimes a
36.
To everyone looking for very specific advice https://www.benkuhn.net/thinkrealhard/
> When I started programming professionally, I was really excited about figuring out how to become a better programmer. (I still am!) So I asked a lot of people, “how can I become a better programmer?” But nobody gave me very satisfactory answers. They would tell me to play around with obscure programming languages, or study algorithms, or read papers, or do a bunch of other stuff that felt tangential and didn’t really move the needle.
> In retrospect, I wish those people had just told me “think real hard.” I was looking for an easy way out—One Weird Trick to Programming Better—but programming is too hard for that.
> That’s my preferred reading of the Feynman Algorithm: there is no one weird trick.
would tell me to play around with obscure programming languages, or study
algorithms, or read papers
37.
Attitude on CP and Codeforces contests. Greetings dear Codeforces community,
I always wanted to write a post that reflects my progress in turning purple after starting competitive programming for three years, and also to record such a _short_ moment, so here it is.
I just reached a 1900+ rating after participating in [contest:1993] by finishing ABC super quickly, meanwhile, six thousand contestants solved them during the contest. So my 'purpleness' is shaky and I wanted to secure it in the upcoming contests.
Yesterday night, when I was studying a certain dp topic, I was asked by my friend [user:YJ365723,2024-08-10] "Do you think problem solving skill in CP is much like sports".
I was intrigued by this analogy. I always treat Codeforces contests pretty seriously, but my initial motive for doing CP is to get a taste of computer science. I then realized doing contests is a way to boost my ego.
Back to the sports analogy, in my case, I do sport solely because I want good health and to entertain myself. People have...
", "problem C in this contest is way too simple/hard"... To be super
straightforward, these complaints
38.
Codeforces WatchR is now available for all iOS users After almost **5 weeks** of studying and working hard, **3 App Store rejects** and a few sleepless nights, we've succeeded to bring [Codeforces WatchR](https://apps.apple.com/us/app/codeforces-watchr-contests/id1495591299) application to iOS.
Download it right now using [this link](https://apps.apple.com/us/app/codeforces-watchr-contests/id1495591299). Don't have an iPhone? Not a problem, it's also available in [Google Play](https://play.google.com/store/apps/details?id=com.bogdan.codeforceswatcher).
It doesn't have all Android features just yet, but we've decided to ship early and often to get the feedback from the community ASAP. The current version has next features:
- browsing and sharing **Recent Actions**
- watching for **Codeforces contests** and adding them to the device's **calendar**
- browsing and searching for **Problems** (marking the as a favourite is coming)
This is the **first-ever iO...
After almost **5 weeks** of studying and working hard, **3 App Store rejects**
and a few sleepless
39.
overwhelmed **Note: it's a mile-long wall of text about my story in the recent ICPC Regional Contest, which is my first time experiencing it, so if I wasted anyone's time, I'm truly sorry.**
<spoiler summary="Backstory">
I kinda lost motivation in Competitive Programming for a while and decided to take a long hiatus since March. I had a lot of work to study and do, given semesters and stuff, and preparing to go to university (I'm 18). It wasn't fun back then. Fast forward to June, when everything was done, I had a bunch of universities to choose from, and it really messed up my mind. Every school felt, equal. It took like a whole 2 months before I chose Hanoi University of Science and Technology (HUST), most probably because it's well-known in Vietnam and has a long and successful history and stuff.
I knew that it was really hard to not choose Vietnam National University (VNU), since it's a really good school and most of the strongest people in programming, especially CP, went there. My s...
long hiatus since March. I had a lot of work to study and do, given semesters
and stuff, and
40.
My Journey as a Beginner Competitive Programmer I’m a 5th semester university student, still struggling to find my place in competitive programming.
I started coding in my 1st semester, full of excitement, thinking I’d improve quickly. But semester after semester, I failed to stay consistent. I’d start, stop, start again — always losing focus halfway through. Now, in my 5th semester, I’m finally trying to hold on to some consistency, to really keep going this time.
Still, things aren’t easy. I can barely solve problems above 800 rating on my own. Sometimes I manage to solve Div. A problems, but most of the time, I can’t even handle the easy ones. My patience runs out fast. I can’t sit with a single problem for too long before my mind drifts away.
And yes, I depend a lot on ChatGPT. Maybe more than most people admit. Some say it’s wrong to rely on it — but honestly, without it, I wouldn’t have learned half the things I know today. YouTube videos teach the basics, but ChatGPT explains those small, detailed things that no vide...
feels like I’m running in circles — trying hard, but not really moving
forward. Even writing, somehow balance everything. Some days it feels like I’m running in circles —
tryinghard, but not
41.
Group tutoring Hi. I offer classes for groups of 2-3 students.
I teach competitive programming with a focus on problem-solving.
There won't be many lectures because I can send you an article/video link instead.
The lesson cycle is usually: I choose a problem, you say your thoughts and ideas, I comment on incorrect ideas, and we talk about the valid solution(s), possibly with drawings and pseudocode.
In beginner groups, I might ask you to implement something, C++ or Python preferred.
There's a lot of homework and you're expected to practice a few hours per week.
We might spend half a lesson talking about 1-2 homework problems from last week.
This is intended.
We use Google Meet, shared whiteboard, and a collaborative editor Codebunk.
After a lesson, you get a video recording and a codebunk with code/text history like this one https://codebunk.com/pb/3501100331621/.
This allows you to copy links and code easily.
There's a Discord group chat to ask questions between classes.
- 1.5h les...
. Please note that your achievements depend mostly on your talent and hard
work, no private coaching
42.
From 0 to ICPC in 1 Year **Welcome to my first blog!!**
<br>
I'll be sharing my journey in the cp world and how I managed to qualify to ICPC 1 year and 3 months (sorry for the clickbait) into my cp career. If you're curious what it took to achieve this, or if you're looking for some motivation or inspiration, this blog is for you :)
<br> A special thank you to [user:alnq417,2024-12-12] for helping me cook this blog <3
<br><br>
### _Starting My CP Career:_ _LCPC 2023 Fail_
One month before LCPC 2023 (Lebanese Collegiate Programming Contest), my university informed me about the competition. I was a second year student at that time so I quickly formed a team and registered, not knowing anything about the competition at all. I had high hopes, thinking it would be something similar to what I was studying at university and I assumed I'd do well.
<br><br>
Fast forward a month, I solved the easiest 4 problems in the competition and r...
/Rilx5irOux)) consisted of 15 problems, most of which are very easy, with only 2
hard problems
43.
Is university degree important? <HTML>
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<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">
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@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...
was once proud of myself for solving a relatively hard problem in the exam
then after the exam I
44.
[Tool] Codeforces Problem Setter: Sort Submissions by Difficulty Rating Hello Codeforces!
I am excited to share a new Chrome Extension I built called [Codeforces Problem Setter](https://chromewebstore.google.com/detail/ehbjoggjihaoggebggekpcgacanhdfil?utm_source=item-share-cb).
### The Inspiration
The idea came to me while reading [this excellent blog post (Entry #124180)](https://codeforces.me/blog/entry/124180). In section 2.7, the author mentioned a resource where someone had manually compiled jiangly's solutions into a PDF book so people could study them by difficulty.
It hit me: "If compiling solutions by difficulty is so useful in a book, why isn't it available directly on our submission pages?"
By default, the Codeforces submissions tab is sorted chronologically. This is fine for contests, but terrible for practice. If you want to review that one 2100 rated problem you solved three months ago, you have to scroll endlessly.
### What it does
This extension allows you to **sort any Submissions page by Problem Rating (Difficulty)** wit...
resource where someone had manually compiled jiangly's solutions into a PDF
book so people couldstudy, tourist or jiangly), sort their solutions by rating, and study how they solve
the exact difficulty
45.
Osijek Competitive Programming Camp 2023 winter — wrap Hi everyone!
<center><a href="https://ocpc.mathos.unios.hr"><img src="https://ocpc.mathos.unios.hr/images/ocpc.svg" height="100px"></a></center>
<center>
<b>Sponsored by</b><br>
<a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london">
<img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="50px" style="margin: 5px 5px 5px 5px;">
</a>
<a href="https://www.think-cell.com/osijek2023"><img src="/predownloaded/97/88/97887beeb75a4601259414b36ecee0160c29d027.svg" height="40px" style="margin: 5px 5px 5px 5px;"></a>
<a href="https://pinely.com/">
<img src="/predownloaded/0a/0f/0a0f3f67435d1f6e467bc7203d4a2090ba8f92cc.svg" height="50px" style="margin: 5px 5px 5px 5px;">
</a>
</center>
The [Osijek competitive programming camp](https://ocpc.mathos.unios.hr) (also see the [announcement](https://codeforces.me/blog/entry/110945) on Codeforces) just concluded last Sunday, on February 26, and I'd lik...
hard to follow, or using references to some advanced techniques, or sometimes
even research papers
46.
Ten Years of Competitive Programming 4 Hey, Codeforces!
I’m AmirReza PourAkhavan, the former Codeforces Contest Coordinator. I let the story become complete and I’m sharing it now.
The story is about a 16-year competitive programmer, who left his family and migrated to another city alone to follow competitive programming. After seven years, he advanced to the International Collegiate Programming Contest World Finals, twice.
Read the previous parts: [1](https://codeforces.me/blog/entry/107465), [2](https://codeforces.me/blog/entry/108838), [3](https://codeforces.me/blog/entry/114356).
**Read the Persian version** [**here**](https://docs.google.com/document/d/e/2PACX-1vSUoFC9tLgDCji6rSCYy-RYoUG1_6uOQnHz_LlLKe6KksWBYWO4r6clDly5YxIgzu1g3Tj31weDxgWz/pub).
What happened previously
===
I was a lone programmer, in a small city, trying to learn CP and prepare for the Iran National Olympiad. It was not as successful as I expected. I tried to change my school and I immigrated to Tehran, alone. I entered AE high s...
testing! Yeah! It seems that he has worked hard enough! And well, nothing has
happened! Arpa, I hope you
47.
The relationship between IQ and CF Rating Hello Codeforces,
I hope everyone is having a great day.
Recently I have been seeing many articles and journals on whether certain skills are inherent or acquired. These articles talk about whether, for a certain skill, one is simply born good at it, or someone works to develop this skill, and over time builds it.
According to R. Plomin, (https://www.scientificamerican.com/article/is-intelligence-hereditary/), genetic differences account for a shocking 50% of cognitive disparity among people. The rest is affected by factors like environment and pure hard work.
Does this mean that those who draw a good hand of cards are more likely to be successful?
Let’s get more specific.
In a study done by the University of Washington, (https://www.sciencedaily.com/releases/2020/03/200302103735.htm), participants “took eight different tests: one that specifically covered numeracy; one that measured language aptitude; and others that assessed attention, problem-solving and memory.”...
people. The rest is affected by factors like environment and pure hard work.
Does this mean that
48.
[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...
. Most of their Codeforces VPs are only at the Div.2 AB level), and it is hard
to imagine how such a
49.
How to attract contestants to Regional OI? #### Introduction
I am writing this blog to get everyone's opinion on attracting more contestants and keeping them engaged to my country's (Cyprus) OI. These are questions asked by me, a participant, not the organizers of the olympiad.
#### Team Selection Contests
Our team selection is composed of 3 rounds (100 points problems, with subtasks, full feedback, no penalty, no live ranking).
- The **first round is a 5-hour contest of 4 problems** (mainly implementation problems, codeforces DIV2B difficulty is the hardest). **200 points** or greater lets you proceed to the next round
- The **second round is a 5-hour contest of 4 problems** (focused on basic graph problems, easy do, binary search, and ad-hoc problems). The **top 16** contestants proceed to the next round
- The **third round is 2 days of 5-hour contests, of 3 problems each** (harder graph and do problems, problems using segment tree/other data structures, hard ad-hoc problems, strings, maths, usually the problems' d...
using segment tree/other data structures, hard ad-hoc problems, strings,
maths, usually the problems
50.
My honest journey to Master in 4 years Hi all, this is my first blog on codeforces. I've just reached Master(+2100) after spending about 4 years on codeforces, and I'd like to talk about what I like and regret about my past decisions regarding practicing for this milestone. I know plenty of GM+s have written such blogs, but I think many of you(like my past self) may find these unrelatable simply because of how good they were from the beginning / how much time they have spent / etc, so I decided to write one of my own humble version. Hopefully some of you may find this helpful for your own journey.
I honestly think it's possible to reach Master level proficiency in around 2 years, even if you're starting from scratch, assuming you practice hard enough with the right materials. This is based on my own experience. I say proficiency and not reaching the rating itself because I think having high codeforces rating may become even more meaningless in the near future with LLMs.
### The Beginning
Like many of you all, I'm j...
you practice hard enough with the right materials. This is based on my own
experience. I say
51.
Every problem I ever made As you may [have seen](https://codeforces.me/contests/writer/flamestorm), I've written a lot of problems.
In this post, I want to go over each of my problems and describe my thought process for how I created each problem. I got this idea from [user:antontrygubO_o,2023-01-21], but I was also inspired by [user:McDic,2023-01-21]'s editorials that included a "behind story" for each problem. Anyway, I thought it would be fun to give you all a glimpse into my thought process: where my ideas came from, the obstacles I encountered along the way, and any random tidbits that give a bit more pizzazz to the problems.
I think it's important to remember that problem-writing is a creative endeavor, so I hope you'll enjoy reading about the making of my problems as much as I enjoyed creating them. And who knows, maybe you'll even be inspired to write some problems of your own.
Also, spoilers for a lot of problems. Obviously.
<table>
<thead>
<tr>
<th>ID</th>
<th>Problem</th>
...
> Codeforces Round #766 Well it looks like I broke my rule about hard/stupid, hard/stupid constructive D2A. In my defense, however, I proposed this as D2B,
and it was moved down
52.
Struggling to Reach Specialist on Codeforces? Looking for Advice! Hello Codeforces community,
I've been working hard to reach the Specialist rank, but I feel like I'm hitting a wall. I've put in quite a bit of effort practicing problems and studying algorithms, yet progress is slow. So, I thought I'd reach out to all of you for advice!
Here’s a bit about what I’ve been doing so far:
- Practicing Basics: I’ve been solving a mix of 1400 and 1500 rating problems to strengthen my understanding of basic algorithms and data structures.
- Focused Practice: I’m trying to work on specific areas like sorting, binary search, and dynamic programming, but sometimes it’s hard to know which topics to prioritize.
- Time Pressure: In contests, I struggle to solve problems fast enough to get a good rating boost.
Questions for You
- How did you break through to the Specialist rank? Was there a specific approach, topic, or routine that helped?
- Any tips for improving speed and accuracy under contest conditions?
- Are there particular topics you found cru...
Hello Codeforces community, I've been working hard to reach the Specialist
rank, but I feel like, I've been working hard to reach the Specialist rank, but I feel like I'm
hitting a wall. I've put
53.
April Fools Day Contest 2018: editorial #### [problem:952A]
JAPE riddle generator is a program which can produce question-answer puns. This problem has been inspired by one of the witticisms produced by it:
What do you call a quirky quantifier?
An odd number.
All you had to do was to check whether the given "quantifier" was "quirky".
#### [problem:952B]
This problem was inspired by the awesome book "Surely You're Joking, Mr. Feynman!" In one of his stories Feynman asks a librarian to fetch him a map of a cat, having a zoological chart in mind. Of course, such a serious interpretation was unsuitable for my purposes :-)
This was a perfectly straightforward problem: just pet the cat!
[cut]
If the reaction you get is "no", try a different spot, otherwise you can figure out what kind of a cat this is right away. Just make sure you're not carried away: both kinds of cats get bored after 7th attempt to pet them and send you away without letting you guess their kind.
One thing I didn't take into account was ...
thinking. It is really hard to win betting on a number or even on two numbers
(although I've seen a
Tutorial of April Fools Contest 2018
54.
Topic : Bit manipulation (Roadmap) <img alt="Logo" src="/predownloaded/63/91/6391eafacef8f14113ae3c6051c58402c1e369f2.png" style="width:35%; height: 35%; margin-left: 30%;
margin-right: auto; max-width: 100.0%;max-height: 100.0%;" />
<br>
In this blog, I will gather some study resources and problem sets to help you understand the topic of bit manipulation. I will provide explanatory videos (in Arabic) followed by easy and medium-level problem sets.<br>
### **<span style="color:#800080">Explanatory Videos</span>**
##### <span style="color:#800080">video 1</span>
Watch [this](https://youtu.be/sK0uVbs_J6Y?si=wAr_tZvI06Z_LYDJ) YouTube video and Learn basic Bit operations. (made by [solver to be](https://solvertobe.com/))<br>
##### <span style="color:#800080">video 2</span>
Watch [this](https://youtu.be/ldwGf-iVsdU?si=ZU-1pMVmmNBlRZwU) YouTube video and Learn more patterns and concepts. (made by [Dr. Mustafa Saad](https://t.me/mostvision))
<hr>
### **<span style="color:#800080">Problem Sets</span>**
These probl...
%;" />
In this blog, I will gather some study resources and problem sets to help you
understand
55.
Tutorial and tips to reach Expert. Before the start of the blog, I'd like to thank [this blog](https://codeforces.me/blog/entry/53341) for motivating me to write it.
However, this blog is quite outdated in many factors like the rating system, and people starting cp in 2020 may have trouble following these. Therefore, I would like to write new tips for doing well in codeforces. The goal is getting to expert, or rating 1600.
I would write this in 3 steps, but the most important thing here is **Practicing hard**. You won't get to 1600 if you don't practice, you don't have to do it on the blog's way, but you should practice.
Step 1: from 1000(grey) to 1200(green)
------------------
First, read [introduction to the new rating system](https://codeforces.me/blog/entry/77890) and judge your skill. Note that you'll need to take part in about 5 contests to judge your skill. If your rating is under 1200, read the next part and practice.
If you use div3, you'll need to solve 3 problems in 30 minutes. That means you...
. I would write this in 3 steps, but the most important thing here is
**Practicinghard**. You won't
56.
DP Tutorial and Problem List Today I've listed some DP tutorials and problems. Actually, I made it for my personal practice. But I think It may Help others too.
Update: I write stuff [Here](https://duoblogger.github.io) in Bengali. I probably have one or two basic DP tutorials too. If you understand Bengali, it may help.
**Note: If you have some other tutorial links and nice problems, mention them. I'll add them here. It'll help me too.**
## Dynamic programming:
* [Topcoder Tutorial](https://www.topcoder.com/community/competitive-programming/tutorials/dynamic-programming-from-novice-to-advanced/)
* [Dynamic Programming,from novice to advanced](https://www.cnblogs.com/drizzlecrj/archive/2007/10/26/939159.html)
* [Learn DP and other tricks](https://www.codechef.com/certification/data-structures-and-algorithms/prepare#foundation)
* [Non-trivial DP tricks](https://codeforces.me/blog/entry/47764)
* [Everything about Dynamic Programming](https://codeforces.me/blog/entry/43256)
* [Digit DP 1](https://...
/inoi/online-study-material/problems/rivers.php) * [Coffee
shop](https://www.iarcs.org.in/inoi
57.
Chinese Teacher:Give up your hobbies at once that take 30+ mins a day! Hello Codeforces!
Today I had a problem with what my teacher said in school.
Our politics teacher, Mrs. Cai, told us something in class about the 'right' way to study for the Junior School Academic Examination that made us doubt.
She started telling us to give up all our hobbies: 'If anything other than studying takes up more than half an hour a day, you must give it up right away! There is nothing more important than the Exam.'She even said,'You have to give up even if you can't!Also,'You should have given it up when you were in Grade 6.’
Someone learnt to play the piano, and it usually took hours to practise, he learnt for a long time and really loved it.Mrs. Cai replied,'If you want to be Ronald, let you go!Do whatever you want!But you have to give up any hobby to waste your time studying as long as you're going to take the Exam.
If we do as what she said:
```
I take part in Codeforces contest for 2 hours.Give it up!
I learn linear alegebra for 3 hours.Give it up...
teacher, Mrs. Cai, told us something in class about the 'right' way to study
for the Junior School, There are counter-Examples everywhere! It's even hard to find a good student
who doesn't have a
58.
5th place curse in Turkish Team Selection Contest and my goodbye Hello, I want to talk about an ongoing curse in Turkey. I am the most recent victim of that curse at it's 9th year. Let's start with the beginning.
#### 2015-2016
Curse starts with [user:ErdemKirez,2023-05-10] taking 5th place in 2015. After that year, he tried his best and was in the team in 2016. But because of some reasons Turkey team wasn't able to participate IOI 2016. After that, the curse has started. You can look at this [blog](https://codeforces.me/blog/entry/54007) for details.
#### 2017
I don't know who was at 5th place that year. But probably curse was active.
#### 2018-2019
In 2018, [user:TahsinEnesKuru,2023-05-10] got 5th place. 3/4 of that team was at their last year so he had a high chance of being in the team at 2019. But he didn't know, he was already cursed. He missed the team with a difference of 3/700. He also has a [blog](https://codeforces.me/blog/entry/66811) about it.
#### 2020
At that year, [user:ExpertHunter,2023-05-10] got 5th place. He was at hi...
anything. Because last years tst really broken me. I am now at 12th grade and
I also need tostudy for
59.
I have solved problems on Codeforces for 500 days in a row It's been a while since I started my journey into competitive programming and in this year and (almost) a half I would say that I learned a bit not only about problem solving but also about myself, so I wanted to share my reflections on some mental aspects of practicing competitive programming hoping they can help someone else.
Please note that these reflections are merely personal and mostly stem from personal experience, if you disagree with something I would like to know your point of view!
I would also like to thank [user:Intellegent,2025-12-08], [user:turska,2025-12-08] and [user:LMeyling,2025-12-08] for proofreading.
#### Some background
I used to do math olympiads for 8 years before starting university, in hindsight I did not really like it that much since I never practiced on my own and would've rather played League of Legends / Minecraft / VALORANT or whatever game I was obsessed at the time. ...
not my main interest and not something that I wanted to study. Now if you are
serious about
60.
Streak... I don't know how many of you can **feel** me, but there is something I need to express to my **Code-Mates**...
I have never been consistent in my life. Never. Since my school days, I always used to plan for something and follow it for no longer than two days. It felt like the universe was conspiring against me. Maybe I was just consistent in one thing — Laziness. I procrastinated on everything, even the things I enjoyed.
Due to this, I failed numerous times. I took motivation from my parents and some friends, got back up, and then failed again. It felt like a non — ending cycle that I couldn't escape.
Even in my competitive journey, if you just look at my profile, you'll see that I joined Codeforces in July. I did it well for two weeks, and then I got some reasons to take a break for two days. And it took me the next three months to realize that I have never been consistent in anything. (Before Codeforces, I spent nearly a year on CC with the same story.)
And th...
per day**. In the beginning, I found it hard to stick to this, but later on,
it became a part of my, **. In the beginning, I found it hard to stick to this, but later on, it became
a part of my habit
61.
As an CNOI Gold Medalist: How I Train CNOI Gold Medal Winning Competitive Programmers This post is about:
1. The Main Two Abilities You Need in Competitive Programming
2. How to Choose Problems of an Appropriate Difficulty
3. How Should You Work on a Problem
4. When You Should Learn New Knowledge (Like New Algorithms)
5. How to Train Before an Important Contest
6. Free Content, Personalized Subscription Services, and Potential Opportunity for One-to-One Coaching
7. Survey About the Services
I won a gold medal at NOI 2024 in my second year of high school and was admitted to the Turing Class at Peking University. After securing my admission, I continued pursuing competitive programming: I began studying new material at university in advance while also challenging myself in higher-level competitions. During the winter of my final year of high school, I competed in the Universal Cup 2025 Finals and placed fifth among many strong contestants from around the world.
At the same time, I became a competitive programming coach because I wanted to give back to the ...
as a competitive activity rather than as the study of an ordinary school
subject. It is more like, competitive programming as a competitive activity rather than as the study of
an ordinary school subject
62.
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 ...
study CS and another in which I'll study medicine, But it is really hard to
make my final decision
63.
OCPC 2024 Fall — wrap Hi everyone!
<center><a href="https://ocpc.mathos.unios.hr"><img src="https://ocpc.mathos.unios.hr/images/ocpc.svg" height="100px"></a>
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<center>
<b>Sponsored by</b><br>
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Last Sunday marked the conclusion of the fourth [Osijek Competitive Programming Camp](https://codeforces.me/blog/...
nevertheless fun. I jokingly called it playing ping pong on hard mode 😁
Overall, the whether
64.
Am I spending too much time on a single problem? Today I solved [this 1600-rated problem](https://codeforces.me/contest/1497/problem/C2). <br/>
I tried this problem (for about 2h+) around one month ago and I wasn't able to solve it then. So I left it for later, without seeing the editorial.<br/>
Today I tried it again in two sittings and devoted 1h + 2h time to it. I was stuck multiple times, but I just wanted to solve it on my own, really didn't want to give up.<br/>
I finally managed to solve it on my own without seeing the editorial.<br/>
Though it was very satisfying to solve it, I am still **confused about whether I wasted too much time(overall 5h+) on this problem**.<br/>
This happens to me a lot. I spend 1.5h+ on average on a problem and it's very common for me to spend around 5-6h+ on some problems.<br/>
Every time I get stuck on a solvable problem and I have the option to jump to the editorial, I am afraid. <br/>
I fear that I will miss the important skill development that I can get if I manage to solve this prob...
65.
Have you regretted quitting competitive programming? I began to learn about CP during the last quarter of my first year at college through the CP community at our university.
I created an account on Codeforces and attempted to solve random problems, often aiming for higher rating problems to prove to myself that I was skilled.
I wasn't following any strategy, and there was no one to guide me. I simply pick random problems with ratings higher than my actual skill level and try to solve them even if it takes me days to do it.
I managed to reach a Specialist with no knowledge. and after gaining some random knowledge in various topics, I stopped training and CP for almost a year, barely solving problems when I was bored. Now, I realized all my mistakes and understand that I wasn't actually training; I was simply wasting my time.
The issue I'm facing now is that I'm in my third year at college, and in my country "Egypt", passing a job interview requires more than just problem solving you also need to know abo...
backend development and study AI for graduation project) So, let me ask you
66.
Way of problemsetter *The mystery of creating rounds unveiled by author of the 4 of them!
The guide for preparing the round without horror-fiction and pastorals!*
Thanks for [user:RodionGork,2014-06-13], who push me to writing this post and thanks for [user:lucAbalo,2014-06-13], who push [user:RodionGork,2014-06-13] to pushing me to writing this post.
Also, many thanks to [user:RodionGork,2014-06-13] for the translation of this post to English.
##1. Inventing problems
It's hard to advise anything on this point. There's no some standard way of creating problems — and if one have existed we'll have only "complicated algorithmic exercises" instead of "problems". People who participated in Russian Code Cup do know well the tasks of that sort.
To cook good and interesting problem there should be some **idea!** which came to your mind (and later to minds of participants of the contest). Even the simplest problems of `A` level for the `Div2` should have some **idea**.
So here is the war...
translation of this post to English. ##1. Inventing problems It's hard to
advise anything on
67.
Remembering Childhood dream ! Before I start programming and studying for ACM, I wanted to be a civil engineer (My dad's job). In Iran, we have to participate in konkoor exam, in order to be able to enter good universities. My score was not that good to be accepted in computer engineering, And so I chose to be a civil engineer and I was accepted to Amirkabir University of technology, 3rd university in Iran. In all semesters, I was saying "oh Man, don't you want to change your Major to computer engineering? The one that you had dreams about becoming a famous ACM er! But, civil engineering was good! I was ranked one in my faculty, so why would I change my major?" I decided to double major with it instead of changing my major completely. But I was still only taking courses from civil eng faculty not any from computer engineering. I was not sure. I already had a good condition at the Civil Engineering faculty on Amirkabir university of technology so why should I ruin it? why shouldn't I continue my masters in it or in ...
as good (and as hard to pass courses) as Amirkabir and that scores would not
be counted in my
68.
Indian ICPC Camp 2024 (and scripts to host your own camps!) Greetings Codeforces!
=====================
IIIT Hyderabad Programming Club is excited to announce Indian ICPC Camp 2024, a collaborative effort from top Indian colleges and universities, sponsored by [Databricks](https://www.databricks.com/). This camp offers an excellent opportunity to advance your skills in competitive programming and team contests.
<center>
<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/6/63/Databricks_Logo.png/440px-Databricks_Logo.png">
</center>
**TL;DR**
First contest will be held on September 22. One contest almost every Sunday. The deadline to fill the form is 23:59 IST, 15 September 2024. Scripts for hosting your own camp at the end.
[Registration Form](https://forms.gle/F6Ttn3KnrGyWXcPh7)
[Discord Server](https://discord.gg/W8xv5kfFay)
About ICPC Camp
---------------
### Contests
We have planned ICPC style contests (5 hours, with difficulties corresponding to Indian regionals and higher) over the next 8+ weeks. Eac...
! Contest Sources --------------- Problem setting is a long and hard task, and
coming up with 8 ICPC
69.
[Consistency] Finding Motivation Hello, CodeForces!
Recently, one of my students had a really bad contest. Even though he worked really hard in the last couple months, he could not pass an important qualifying round of an arguably easy, new, Romanian contest. The first 4 'official' contestants qualified, and sadly he was the fifth. He was really upset after the contest, and had a hard time gathering enough motivation/discipline to continue working, because there were scenarios in his head such as "what if this will happen in training camp?" or "what not passing had a really bad turn on my future?"
Today, I am going to share with you all a simple method that can help you get over a bad contest or just motivate you to work more in general. Keep in mind, I am not a specialist in this domain, I am only a teacher with experience, so there might be better methods out there, but throughout the years I have seen that what you are about to read worked best on many of the my students. I advise you to also read this great ...
really hard in the last couple months, he could not pass an important
qualifying round of an
70.
hard situation hello everyone, I would be glad if you would share your opinion about my situation, I just can't decide whether I should continue to engage in competitive programming or stop doing Olympic programming. a year and a half has passed since I started doing competitive programming. last year I passed the school stage of the Republican Olympiad and could not go further to the third stage.
after that, I only solved Div2A, but then I started solving other tasks from other platforms and Div2 B. I also tried different ways to study competitive programming, but since then there has been no noticeable progress (I still continue to study like this) one year has passed? and today the school stage of the republican Olympiad has passed. most likely I didn't pass this year, let alone the next stage. should I continue to do sports programming or stop doing it. I also study in the 10th grade, I have 2 two years before graduation and I also need to do a bunch of things to get into university, I myself wa...
hard situation, tried different ways to study competitive programming, but since then there
has been no noticeable
71.
Any solution to the problem of 'aging'? Dear competitive coders,
(this is as lengthy as 'Codeforces problem statements' and irrelevant to improving your skills, so never mind it if you are short of time, but if you could read it and find an 'AC solution' to my problem, I would like to deeply appreciate it)
The past 2 years made the most tedious period of my life. Time has revealed to me a miserable truth that I am too old to be a coder or even anything. If one takes a look at my rating graph, it would be crystal clear that my 2 years of lifetime has been wasted. The line was just fluctuating around some certain points depending on my emotional states (approximately 1600 at first, then 1850 thanks to the recent "Rating Inflation", I was actually happy with it for a while though). No improvement, yeah, 2 years without any improvement at all. I start to wonder if I am really aging that fast.
Never can I forget the first time I started coding, 8 years ago. When my friends were learning Excel, I was coding my the first inf...
and the ";" for something more beautiful :p and receive red warnings all over
the windows, buthard, beautiful :p and receive red warnings all over the windows, but hard work
beats smart mind, I made
72.
How do you progress when you feel stuck? Hello CodeForces!
This is my first time writing a blog post so please hang on with me c:
I'm currently a student in US studying Computer Science/Engineering. I never focused much on programming like my fellow peers in the Uni I go to (some of them apparently did USACO or some form of olympiad), and I have this feeling that I'm falling back behind regardless of how hard I try in school. # Note that I do have some mathematics background, qualifying for AIME with a score of 9 (which isn't that amazing, but still something).
However, that feeling of falling behind is the reason I started doing CodeForces again (did a few competitions freshman yr), with a sole objective to become a better coder.
The problem is:
I'm able to solve first two problems in D2, but cannot seem to find solutions for the next few problems. However, the topics in C and D in D2 problem sets are topics that I'm relatively familiar with, but only after I read the editorial I understand how to apply these...
olympiad), and I have this feeling that I'm falling back behind regardless of
howhard I try in school, ), and I have this feeling that I'm falling back behind regardless of how hard
I try in school
73.
[Tutorial] Generating Functions in Competitive Programming (Part 2) Welcome to Part 2 of my tutorial on generating functions. The [first part](https://codeforces.me/blog/entry/77468) focused on introducing generating functions to those without any background in generating functions. In this post, I will demonstrate a few applications of generating functions in CP problems. Let us start with some relatively straightforward examples.
Note: Unless stated otherwise, all computations are done modulo a convenient prime (usually $998244353$). Also, $[n]$ denotes the set $\\{1,2,...,n\\}$.
### Blatant Applications in Counting Problems
**Problem.** [AGC 005 Problem F](https://atcoder.jp/contests/agc005/tasks/agc005_f) You have a tree $T$ with $n$ vertices. For a subset $S$ of vertices, let $f(S)$ denote the minimum number of vertices in a subtree of $T$ which contains all vertices in $S$. For all $1 \le k \le n$, find the sum of $f(S)$ over all subsets $S$ with $|S| = k$.
Constraints: $n \le 2 \cdot 10^{5}$.
<spoiler summary="Solution">
First, ...
and usually the hard part is to reduce your sums into a form that can be seen
as the convolution of
74.
First RED-INDIAN AI Cheater? **NOTE: RED INDIAN IN THIS BLOG DOESN'T REFER TO THE NATIVE AMERICAN RACE. IN THE CONTEXT OF THIS BLOG, RED-INDIAN REFERS TO AN INDIAN WHO CHEATED HIS WAY TO RED, THAT IS, GRANDMASTER.**
The person I am going to talk about here is none other than the most recent Indian Red Coder [user:arnabmanna,2025-04-27], who achieved this feat in the last Division 1, [contest:2097] after solving 4 problems and getting a Global Rank of 62 and India Rank 1 in the contest, giving him a whooping 119 rating boost. Such a jump not only made him red but also made him surpass 2 existing Red Coders [user:cerberus97,2025-04-27] and [user:invertedwinger,2025-04-27] in all time India leader board, making him the 5th highest rated coder in India and 582nd Globally.
His progress seems very inspirational (for a certain group of people who follow his footsteps) since he achieved this feat with just 425 problems solved for all time, 74 of which happen to be 800s. Not just this, he went from Newbie to Gr...
. Coincidently, AI researchers and Future AI Anthropologists who happen to study
the evolution of AI
75.
Running a College Club (Somewhat Successfully) #It’s just a club
https://www.youtube.com/watch?v=GzPqp1gWfe4&t=633s
If it is, don’t read ahead. You lack passion for running it. Just think of it, what in this modern world has been accomplished without passion. Nothing. People really loved something, were driven by something and that is why pursued it. Not just because it was a means to an end. If it was, it didn’t end up as great.
It fulfils a mission that you truly believe in and want to spread. You really are happy when the members of the club succeed or even surpass you. You just become selfless and give yourself to the club. This is when the club thrives. You think what’s best for the club, not for you. You are the Mother, (he he he).
College Clubs (in India) are rarely run by passionate people. They just want to maintain what had happened last year, or keep doing the same kind of stuff. It’s never new. The issue is that, the majority of the people’s purpose for being in the club is getting an LoR from their faculties...
within, only and only then will the members work hard for the club. It’s a
niche group of cool
76.
Specialists are the Real Lower Class of Codeforces # Specialists are the Most Annoying Rating Bracket and objectively the Worst of the Lower Class on Codeforces
Newbies are new. Candidate Masters are actually pretty good. Masters and above have already proven themselves. Specialists, meanwhile, have somehow managed to combine the confidence of a seasoned competitor with the accomplishments of someone who still gets stuck on Problem C every other contest.
A Specialist's entire personality consists of being exactly one contest away from greatness. They don't solve hard problems; they almost solve hard problems. They don't become Experts; they are about to become Experts. They don't improve; they have a training plan that will definitely work starting next week. Every conversation eventually circles back to the fact that they're on the verge of a breakthrough that has somehow been imminent for the last two years.
Every Specialist also has a detailed explanation for why their current rating is fake. They're underrated. They're unl...
greatness. They don't solve hard problems; they almost solve hard problems.
They don't become Experts
77.
Gap Check: Free Adaptive Coding Skill Diagnostic Tool Hey Codeforces!
We're Codetree — a bunch of competitive programmers and former IOI/ICPC medalists who grew up grinding contests right here. This community shaped us, and now we want to give something back.
**We've all seen the struggle:**
- Grinding CF for interview prep but stuck at Grey/Green/Cyan despite putting in hours
- Can't seem to break out of DIV 3/4 contests
- No idea if you're actually getting better or just spinning wheels
- Watching others climb while you feel stuck
Been there. It sucks.
So we built something we wish we had years ago: Gap Check — a **completely free** tool that exposes the difference between what you think you know and what you actually know.
**How it works:**
1. Choose your starting point:
- Just jump right in!
- Pick an algorithm tag you're studying
- Link a Leetcode problem you've been working on
- The Codeforces problem linking feature is currently under maintenance.
2. Our adaptive testing ...
78.
not sure next step of my life — Would appreciate your advice Hello Codeforcers,
I find myself facing a challenging situation in my career and I would like to share my story. I graduated from uni about two years ago with a major in Electrical & Electronic Engineering. However, during my time in university, I realized that my true passion lies in algorithms and computing. So, I decided to take a risk and pursue a career as a programmer/software engineer while simultaneously completing my major coursework. I worked hard and managed to secure internships immediately after college. I was fortunate enough to be hired by big tech company X. After working there for a year, I sought new challenges and applied to Amazon, where I was hired as a entry-level(L4) software development engineer.
Initially, everything seemed to be going well and I was grateful for my hard work and self-motivation that led me to where I am today. However, things took a turn for the worse. After a few months at Amazon, I was assigned to a project that proved to be extremely ...
while simultaneously completing my major coursework. I worked hard and managed
to secure internships
79.
To admins (cheater report) Hello everyone, I want to report 2 cheaters today.
2 days ago there was CF Round #395 Div2. I participated in contest also, problems were really good. Let's look [standings](http://codeforces.me/contest/764/standings). Hmm, good, 3 people solved all problems, 2 of them are Chinese. [user:ljh2000,2017-02-04] and [user:MashiroSky,2017-02-04]. Ok, I looked their profiles, saw that they are living in same place, studying in same school. Hmm, it doesn't like coincidence. Then I looked their solutions.
Solutions for problem A: [user:ljh2000,2017-02-04]'s [solution](http://codeforces.me/contest/764/submission/24367006), and [user:MashiroSky,2017-02-04]'s [solution](http://codeforces.me/contest/764/submission/24365605). Looks similar, but it's easy problem, most peoples solutions looks same.
Solutions for problem B: [user:ljh2000,2017-02-04]'s [solution](http://codeforces.me/contest/764/submission/24369314), [user:MashiroSky,2017-02-04]'s [solution](http://codeforces.me/contest...
, and other one wrote things in work function in main. THEY'RE CHEATING HARD!!!
How Codeforces
80.
Harsh Truth of diversity hiring and difficulties faced by mens. Actually I want to talk about diversity hiring or inclusive hiring that is happening in most of the engineering colleges. We literally receive tons of emails about only-women hiring, only for female candidates, girls who code and bla bla bla.
So I read about it, and found that it was introduced to help so called "weaker-sections of society" so that they can get equal opportunities in STEM fields. In India, this "weaker-sections" mainly includes mostly women only (in USA also includes black people). See, i appreciate the thinking that there should be equal opportunities for men and women and other genders as well. But, what is disheartening is that, in order to achieve so called "equality" these companies and corporates have now become biased for female candidates. There are separate hiring drives only for women, separate training and internship programs especially focussed on women, there are these coding competitions all these are held by big companies like Twitter, Google, Uber et...
i asked this and they gave bizarre logic that the society was patriarchal,
women have ithard, they
81.
Open Problems in Algorithms Research for Ph.D. at Indiana University Hi all,
This is a follow-up on my previous blog post about Ph.D. positions in Algorithms and Machine Learning at Indiana University, USA (http://codeforces.me/blog/entry/45559 ). For the details about the application process see the original post and this link: http://grigory.us/phd-call.html (deadline for full applications is Dec 01, 2016).
Since that post generated some interest I have compiled a list of possible open problems in algorithms research to consider during a Ph.D.: https://www.dropbox.com/s/4mf2b6f9fa9rx91/open-new.pdf?dl=0 It is also intended to give one a sense of how modern research in algorithms looks like. The list includes a diverse set of problems covering massively parallel computation, clustering, various forms of graph sparsification, algorithmic questions in testing analytic properties of high-dimensional functions used in machine learning and topics in communication complexity.
Please, note that most of these problems are quite hard and have been stu...
communication complexity. Please, note that most of these problems are quite
hard and have been, Please, note that most of these problems are quite hard and have been studied
by many researchers
82.
Finally expert! Hi all! I want to write 'cause I am totally happy about my last ranking promotion; to expert!
It have been now 3 years of hard work, and, let me say, It is worth! Who can say learning is boring?
I still remember the old days, in IOI2015, That times I was weak and still very shy. I was a mosquito, and IOI the bazooka.
Moreover, one fact I would like to share: I am currently not aiming to be a computer scientist, I am currently studying to be a electronics engineer, so this is not my principal field. However computer science is widely used here and I find, to learn it very complementary, it helps me with my field, although it is not strictly central, It is something not very well taught in my courses but that is it useful.
I hope you all the best wishes! Ask me problems if you need help :) I love trying to explain hard things.
! It have been now 3 years of hard work, and, let me say, It is worth! Who can
say learning is boring
83.
(Kind of) A brief overview about the near future of Competitive Programming Think about this. In the near future, let's say 10-15 years, technology will improve drastically, and artificial intelligence (AI) will probably be a very important thing in daily life and work. What would be its effect on Competitive Programming? This topic is not new, Every 1-2 years there's someone talking about it on numerous platforms. And probably all received the same answer: It's dubious, only time will tell us, which is true. But in some way, we can just imagine and make probable guesses about what may happen to CP in the future. This blog will mostly summarize my guesses and questions about the near future of CP, and we can discuss it somewhat to hope for an even better community in the future.
#### **I. Competitive Programming Problems**
One thing we can agree with is in the near future, with a huge potential in the CP community and the existence of AI, the quality of the problems may be better. The knowledge standard will increase over time, to match the improvement o...
this will be a hard thing to get with. But with a lot of problems having a
little bit of something
84.
2147G Number Theory Approach # G. Modular Tetration — a Number Theory Solution
## Preliminary Comments
I deleted the first post and am publishing a new one with preliminary comments. This problem turned out to be problematic and spoiled the contest for strong participants, since some cheaters copied it, but it didn’t seem difficult to me, except for deriving the final formula and a bit of implementation. During the contest, I managed to work out the implementation on paper, but I couldn’t handle the coding.
I am a junior in mathematics, focusing on number theory and algebra (at the last JBMO I managed to solve both of these topics), but I still have many gaps in CP and implementation. In number theory I solve or make substantial progress on many problems from IMO shortlists. If you assign a CF-like rating to those problems, I solve problems steadily up to 2000, sometimes up to 2500, and there have been harder ones.
Now I want to use number theory and mathematical implementation of programming problems ...
paper, everything else is psychologically easier to study, learn new things
and thus grow. The main
85.
How to prepare for ACM ICPC? Well I would suggest you to check out Programming Competition,Programming Contest,Online Computer Programming. Here is the details about as the codechef team promote the students for ACM-ICPC or you can also check out the actual university site which conduct ICPC The ACM-ICPC International Collegiate Programming Contest
And to practice problems you can you can refer following sites
1. http://codechef.com
2. http://spoj.com
3. http://hackerrank.com
4. http://codecademy.com
5. http://topcoder.com
6. http://codeforces.com
Good Luck...
for the details about ACM-ICPC 2015 you can read the details ACM ICPC 2015 | CodeChef.
I hope you'll find most of the things...
Here are some steps to get started and be good at it.
Get comfortable writing code in either of one of these languages C, C++ or Java. Why only C, C++ or Java? Because these are the standard languages allowed in any programming competition.
If you are already good at C, it is suggested to learn C++. It...
not focused, I go watch a stupid video on youtube and the whole day is gone.
It is reallyhard for, try to completely change your schedule and study and practice in all of your
free time. Completely
86.
We teach wrong When I was a child, I knew software development well (though not much of C++), and my parents motivated me to try out competitive programming.
The first thing I tried was dkirienko's section. In the first 20 minutes, GCD and the Euclidian algorithm were explained, the complexity of the Euclidian algorithm was proven, and that was pretty much it. We were then asked to solve a problem set on Codeforces individually. I didn't understand much from the complexity proof, couldn't solve a single problem, failed to figure out what I was supposed to do, and left crying. So yeah, stuff like that doesn't work.
I understood simpler topics, though. I knew basic math, like how to solve linear systems and quadratic equations, and could make simple observations, so the school stage of ROI was quite easy to get through. (The hardest part was to explain to my then-informatics teacher that yes, I want the adult problems.) During the municipal stage, I had 3 hours to solve what I'd classify as a 5-t...
" or as hard as "use five linear passes". In a roundabout way, solving
algorithmic problems gave
87.
100 days into competitive programing Hey everyone! This is my first blog and I'm not a native speaker so I'm sorry for any grammar mistakes I might make here.
I've tried to start in competitive programming at the end of September after the ICPC South America Brazil, but i was so bad at this that i got frustrated and i gave up pretty quickly.
Some time later, in October i started to study it and try to get better at this for real. Today is the 100th day I've been doing problems every single day (I personally didn't think i would get this far but here we are). I had a personal goal to become pupil by the end of 2025 but i couldn't make it by then. **BUT** in the Hello 2026 for the first time I've done 4 questions in a global round and reached it!! (i ended up falling to newbie again in the last div.3 but its alright)
#### Why I'm posting this blog
Well, apart from celebrating my achievement, i want to encourage some people that might...
pretty quickly. Some time later, in October i started to study it and try to
get better at this for
88.
Codeforces contests performance improving tips ^^ _Recently, I've successfully promoted to become a candidate master on Codeforces, which is one of my target this year. And to celebrate this, here is my first blog on Codeforces._
**Climbing ranks on Codeforces takes time** _(unless if you known the platform and the contests well in the first place)_. During that time, by pushing yourself to climb to your target ratings, you might find out that you learned a lot. E.g.: more efficient coding skills and strategies, more cohesive thinking and more creative algorithms or uses of data structures,.... That's why I always tell myself
[cut]
that decreasing of ratings is okay, as long as you learned something after _\*that\*_ contest. That's the first tips on climbing: **To have a positive mindset**.
I heard some avoids rating decrease by violating contest rules (for example: submitting others' codes) and get a _"skip"_ after the system calculating rating changes. I think this is not showing the sportsmanship and fairness when partici...
well. - **Check** the _editorial_: try to follow it. If some tasks are too hard
, you can skip
89.
Topic-wise practice resources Today, I will be sharing some topic-wise practice resources...
Practice by Topic – Recommended Resources:
**YouKn0wWho Academy** is a platform where problems are organized topic-wise, and each topic contains standard problems sorted by difficulty levels such as Easy, Medium, Hard, and Very Hard.
This site is extremely useful for beginners because it provides a clear learning path — which topic to learn first, and what to study next.
It also suggests the appropriate problem rating for each topic, helping learners improve step-by-step.
Overall, it's a great resource for beginners to build a strong foundation.
(https://youkn0wwho.academy/topic-list)
**LightOJ** offers a topic-wise problem list with categorized difficulty levels such as Easy, Medium, and Hard.
A big advantage is that it also includes previous ICPC problems, making it a perfect platform for competitive programming preparation.
Highly recommended for intermediate-level learners.
(https://lightoj.com/pro...
contains standard problems sorted by difficulty levels such as Easy, Medium,
Hard, and Very Hard. This, each topic contains standard problems sorted by difficulty levels such as
Easy, Medium,Hard, and
90.
Representation of an integer into sum of eight squares Disclaimer: This might enter the realm of mathematical trickery, and not competitive programming itself, but I think it's beautiful enough to mention it here in Codeforces, and maybe invite some competitive programmers to somewhere else where I've recently moved to...
Problem
------------------
Given an integer $0 \leq N \leq 10^9$ as input. Count how many $8$-tuple $x \in \mathbb{Z}^8$ are there such that $x_1^2 + \dots + x_8^2 = N$. The answer may be large, so just output the answer modulo $10^9+7$.
Ideas
------------------
Obvious brute-force takes $O(N^8)$. Observing that iterating in the square root range is enough reduces it to $O(\sqrt{N}^8) = O(N^4)$. Trying to divide the problems into two $4$-tuples with $x_1^2+x_2^2+x_3^2+x_4^2 = M$ and $x_5^2+x_6^2+x_7^2+x_8^2 = N-M$ reduces to $O(N \cdot \sqrt{N}^4) = O(N^3)$. Reformulating the problem into DP/Knapsack gives an $O(N^{\frac{3}{2}})$ algorithm. Can we do better?
It turns out that in this case, there is an exp...
a self-study notes to actually go through and internalize what I've learned.
Please let me know
91.
ICPC 2015/16 Study Group Hello, I'll be preparing more seriously for this years subregionals/regionals for the months to come. So I thought this would be a good idea.
I've created a mailing list for a study group here: https://groups.google.com/forum/#!forum/icpc-2016-study-group
The idea is to create a study group where whenever we find a good problem that helped we learn something new in a good way, or some good materials to learn something, etc, we share so we can help each other prepare better for the ICPC this year. Or maybe motivate ourselves and push each other to work harder as well.
(For asking questions I think it's probably better to do it here because then more people can see it/learn from it, but maybe in a study group we can ask more "silly" stuff without being afraid as well lol).
Anyone that wants to join is welcome, but please contribute if you do so! =)
ICPC 2015/16 Study Group, come. So I thought this would be a good idea. I've created a mailing list for a
study group here, The idea is to create a study group where whenever we find a good problem that
helped we learn
92.
[Archive] My Father is Ratist **UPD 26/10/2023**: I find this blog very funny and a very relatable pasta for some of us, so rather than archiving it, I'll just post this. By the way, please to all the people out there. Don't feel like practicing CP a burden. It's something you should enjoy, and if you don't please quit. My relationship with my father doesn't get any better since I've posted this two years ago. But at least now that I'm turning 21 makes my brain a bit more considerate to people.
---
Hi everyone. Competitive programming is an entertaining activity. I love it, and it really helps me even in my daily university courses I had. I've been doing CP for 5 years (well, I had breaks in between and other stuff to do and study besides doing cp).
This post is not a rant or a "hello sir, can you help me improve in cp"-type of post. I just wanna share some story that makes me sad. But don't feel pity for me and say I'm a crybaby and I should get good. I'm in catch with my goal and trying my best.
I don...
stuff to do and study besides doing cp). This post is not a rant or a "hello
sir, can you help me
93.
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...
] shared with me HLD-based solution for distinct substrings on segment, which
was toohard for me to
94.
Breaks between tasks (or their absence) **Sometimes it’s harder to tear yourself away from tasks than it is to solve the tasks themselves**, because a non-standard solution might “pop up” at any moment. Therefore, different people handle the need for rest in different ways. Below are four typical CodeForces characters, each of whom has their own attitude toward time-outs between rounds:
**Someone who is always online**
Seems like they have ten CodeForces tabs open simultaneously: during lunch breaks, in class, and even before bed. Do they even take any breaks? Their main principle is: “ _It’s better to be intensely focused on something than to do nothing._”
**The snack lover** ( _5–10 minute breaks_ )
These participants have the superpower to instantly switch from pressing the space bar to grabbing a sandwich. For them, it’s important to give the mind a short rest so it doesn’t overheat. They believe that a quick dash to the kitchen for a cup of tea can work wonders: after all, your thinking process is more efficient...
95.
I'm back! If you asked...lol Someone dmed me and asked me how I was doing.
First off, today was a great day, with a long break due to high school in the States, thanksgiving has allowed me to do some codeforces rounds!
At first, I dropped quite a bit in rating (even going back to newbie!). However, I pushed through and today it paid off. All the stars aligned. It was like magic. I didn't even get a single wrong answer. It was almost too easy.
137th without unofficial, and 62nd with only trusted individuals. Pretty awesome.
As for training, after I had school, I would try to push myself and do some challenging problems. Also, I started reading more. When I was waiting in my school's lunch line, I would read about anything computer science-related. Binary Tree, Heaps, Hashing, things that are not just competitive programming related, just to have fun. I think a lot of people look towards results too much. (As do I) But especially...
for where I was, I had to do school lol. I have SATs to study (it's a
standardized test for many
96.
I Reached GM! Hello, codeforces community,
After the last round of 2024, [contest: 2053], I finally reached Grandmaster (GM)—an achievement I had dreamed of ever since I became a Master 2 years ago, but doubted I could achieve. In Spring 2024 I set myself a goal to reach GM before the end of 2024, which felt ambitious and even unrealistic at times. But here I am, thrilled to share that I have accomplished my goal!
Some of you have noticed that upon reaching 2400 rating I used magic to change my rank to CM. Why? For two reasons: first, I quite like the CM color. Perhaps it is because CM seemed like such a cool rank when I started. Second, I wanted to give myself more time to write this blog, so I hope you will enjoy it!
While some of you might know me, I assume most are seeing my name for the first time. Allow me to introduce myself briefly. I am a 19-year-old Serbian competitive programmer who has been doing CP for around 8 years now. My journey is filled with many highs and lows — ma...
codeforces.** When you are just starting and do not even know ifs and for
loops, codeforces is quitehard
97.
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 ...
think hard on them. The foreigners had to hand in everything taking into
account the penalty time
98.
IOI 2026 day 1 — My solutions for them 
Since there is not much discussion going on I decided to make a post about my solution for the problem, be aware that I will go straight to the full point solution and won't discuss the partial score to save time for you. I'm quite busy lately so I don't have enough time to implement the code and submit to the online judge. Please give your opinion with your comments
**P1**
Putting ball with a value in the leaves, it will ascend to the root as much as possible and only stop when another ball blocking them, then harvest from them the dfs order of the vertices based on the value of the ball on each vertex, then discard all the balls and begin anew.
There is a limit on how many different value you can use (B) and number of them you harvest (K) that seems quite low compared to number of vertices (N ~ 1000) and leaves (M ~ 200) (B + K <= 44)
An unga bunga experiment you will urge to try is simply to c...
observation to overcome the (201 > 44) wall : If we want to study how leaves T
+ 1, T + 2, ..., connect to
99.
What Happens When You Do CP Without Discipline > This isn’t one of those "how I became Candidate Master in 6 months" stories.
> This is what happens when you say "I’ll do it tomorrow" for 3 straight years.
I’m not red. Not purple. Hell, I’m not even consistent.
I’m just someone who started CP with big dreams — and then made every mistake possible.
If you’re stuck, lazy, unmotivated, scared, or feeling like you’re not improving...
**Read this before you waste the same time I did.**
---
## Mistake #1: Practicing only when I felt motivated
I’d solve 5 problems in one random burst, feel proud… and then disappear for 10 days.
I blamed mood, college, stress, sleep.
But here’s the thing:
> CP doesn’t care how you feel.
> If you're not consistent, you're not improving.
---
## Mistake #2: Clicking the editorial the second I got scared
I’d read the statement. Felt hard. Editorial. Copy-paste. Move on.
And then I told myself, "Well, at least I understood the idea."
No. I didn’t.
> I skippe...
editorial the second I got scared I’d read the statement. Felt hard.
Editorial. Copy-paste. Move
100.
Red coders strategy Hello Codeforces
Nowadays I am preparing for ACM-ICPC regional finals, I became master 2 months ago, but I think its by luck, because I have solved a lot of problems(almost 2500) and I know typical problems, therefore I solve them very fast(speedforces), because I have experience with them.
What I want to know how to go further, I think its hardest level to become red coder from master, what strategy should I use, I have seen a lot of people who stuck at orange for many years and some people who are becoming red coder from orange in 6 months.
I have set up my target as becoming International Master till Regional Finals(April 2021) and I believe in the last 2 years of my study I will go to ICPC Finals
Thank you, GL & HF
International Master till Regional Finals(April 2021) and I believe in the
last 2 years of mystudy I
101.
Overview of the Moscow International Workshop @MIPT Recently I returned from the Workshop and wanna share my impressions.
The post will be divided into several parts depending on an aspect I am covering in it.
[cut]
<be/>
####**Place**<br/>
The Workshop is held entirely in MIPT: contestants live in MIPT dorm and have the trainings&lectures at MIPT study buildings. The most distant points in this system are at most five minutes from each other and it was really nice, since one shouldn't care about getting up 30 minutes earlier in order to come to the contest in time. <br/>
In CIS the word "dorm" itself is quite scary, because almost everybody has a vivid experience of coming to some competition to some city called N-vodsk and living in cold, stinky dorm with no water or something like this. However, all the contestants were settled in a new dorm, which was pretty nice and comfortable as for a dorm. I had four guys, including me, living in a two-rooms flat with kitchen and bath.<br/>
Canteen... Well, as for CIS, it was OK, b...
&lectures at MIPT study buildings. The most distant points in this system are
at most five minutes from
102.
Our adventures on Unicamp 2026 Introduction
==================
Over the past two weeks, my friends [user:jackson.souza,2026-01-31], [user:pedrinho_eu,2026-01-31], [user:holanda2103,2026-01-31], [user:realani,2026-01-31], and I attended the ICPC Brazilian Summer School — an event that brings together competitive programming students from Latin America. During this time, we studied full-time, fully focused on the competitions that will take place throughout the year.
Also, we had some cool adventures that I would like to share with you.
1. The water
------------------
When we arrived, one of the first things we realized we needed was water. We went to the mall, but the Carrefour was already closed. So we stopped by a small local market on the way to the hotel where we would be staying for the next few weeks.
At that point, [user:realani,2026-01-31] and [user:holanda2103,2026-01-31] decided to head back to the hotel, while the rest of us stayed behind to deal with the water situation. As they were lea...
most athletic people in the world. The bags dug painfully into our fingers,
pullinghard against
103.
Catalan Numbers and Generating Uniform Balanced Bracket Sequences Hi everyone! Today [user:nor,2022-05-27] sir and I would like to talk about generating uniform bracket sequences. Over the past few years when preparing test cases, I have had to generate a uniform bracket sequence a few times. Unfortunately I could not figure out how, so I would like to write a blog about this now. Hopefully this blog would be useful to future problem setters :) Scroll down to the end of the blog to copy our generators.
First, let's define some things. A bracket sequence is a string with $n$ $\texttt{(}$ s and $n$ $\texttt{)}$ s. A **balanced** brackets sequence is a bracket sequence with the additional constraint that it becomes a valid arithmetic expression when we add some $\texttt{1}$ s and $\texttt{+}$ s. Let $p$ be the prefix sum array of a bracket sequence (we assign $1$ to $\texttt{(}$ and $-1$ to $\texttt{)}$ and take the prefix sum). For example, if our bracket sequence is $\texttt{())()((())}$, then $p=[1,0,-1,0,-1,0,1,2,1,0]$.
An alternate way to thi...
too hard and you should prove it yourself, but for completeness, I will put it
here.
104.
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...
anytime and let me tell you, he was a monster. It was so hard to keep up with
him even though he was
105.
ECPC Teens qualification contest 2024 Hallo everyone,
I'm writing this post just to be a memory about that day.
Few days ago (exactly on **22/7/2024**), me and my teammate [user:youssef_hany,2024-07-27] participated in the ECPC Teens qualification contest.
It was our first time, we have been preparing for it for months.
Unfortunately, we were not qualified to participate in the next division as there was some issues in the problemset and it was inappropriate as all the problems were either too easy or too hard.
Overall the experience was great, we solved 5 problems and we were trying to solve the 6th one for the last second, we had a lot of fun.
So hope that we can participate the next year, it will be exhausting because we will be in 3rd secondary which requires much effort to study and solve problems at the same time.
congratulations for the qualified teams and wait for us next year ;-)
Finally I'd like to thank [user:zyadhany,2024-07-27] for supporting us and helping us in the preparations (he is...
the problemset and it was inappropriate as all the problems were either too
easy or toohard
106.
[Tutorial] Hungarian algorithm in Õ(mn) or O(n^3) I once read a paper that claimed and used the fact that the Hungarian algorithm can be
implemented in such a way that it runs in $O(m n \log n)$ time. Using the soft-O notation which ignores
log factors, the complexity can be written as $\tilde{O} (m n)$. If the graph is dense, i.e. $m = \Theta(n^2)$, the log factor can be removed
There are many tutorials on how to get $O(n^3)$, but I couldn't find any references that directly show how
to do $\tilde{O}(mn)$ from end to end (but I found just enough to conclude that it is probably possible).
So I decided to write one up myself and well, this is as good a place as any.
In my [last blog](https://codeforces.me/blog/entry/128552), I showed how thinking in terms of linear programming and duality can be useful when working with maximum flows and minimum cuts. The usefulness of this is best demonstrated with examples, and this is a good example. In fact, this is pretty much **the** primal-dual algorithm: it was one of the prototypes th...
intuition of the concept. As I said, this algorithm makes a nice case study of
linear programming and
107.
Subject-based Math Practice Hey! As you all study up math in preparation for the next MathForces round, would love to share some subject-based problem sets compiled from old competitions that you may enjoy. Each of these was chosen because they were either nice or educational. They each have a difficulty rating — if there are any you find uninteresting, I'd recommend trying ones of a higher difficulty!
The fun part about these is you can do them in a competitive setting against a lot of other contestants, with a rating :)
Hope you enjoy! (Higher difficulty rating means harder)
[Algebra Set 1 #1 (800)](https://mathdash.com/contest/one-problem-contest-8693400215) <br />
[Algebra Set 1 #2 (800)](https://mathdash.com/contest/one-problem-contest-8801443023) <br />
[Algebra Set 1 #3 (1200)](https://mathdash.com/contest/one-problem-contest-5930391188) <br />
[Algebra Set 1 #4 (1200)](https://mathdash.com/contest/one-problem-contest-8922939634) <br />
[Algebra Set 1 #5 (1200)](https://mathdash.com/c...
Hey! As you all study up math in preparation for the next MathForces round,
would love to share
108.
How Can I Solve Problems Harder Than 800 Rating? Hello, I am Gustavo from Brazil.
I would like some tips to help me improve. Currently, I can solve problems rated around 800 in Div. 4. I can solve problems A, B, and C in Div. 4 contests, but no more than that. In Div. 3, I can sometimes solve problem A, but I don’t know what to study to improve.
I’m in my first year of Computer Science and about to start my second semester. So far, I’ve only had one introductory algorithms course at university. I’ve learned about stacks, queues, sets, multisets, vectors, pairs, and algorithms like sort, upper_bound, and lower_bound. At the beginning of this year, I’ll also learn about trees.
I’ve attached an image of my solved problems. Most of them are rated 800, and I’ve solved 86 of them so far.
What should I do to get better? Any advice is welcome!
more than that. In Div. 3, I can sometimes solve problem A, but I don’t know
what tostudy to, sometimes solve problem A, but I don’t know what to study to improve.
109.
EQ Technologic Interview Experience In this particular blog, I am going to share my interview Experience with EQ Technologic. It was in mid — June when I received a mail from the recruiter for the Software Developer Role, University Graduate (2022).
Day 1: Online Assessment
========================
I received a mail regarding the aptitude and coding round. The exam is divided into 2 sections.
Section 1: Aptitude
-------------------
Consists of 14 questions of Logical Reasoning. The total duration of this section was 14 minutes and I was able to attempt 11–12 questions. The level of Questions varies from Easy to Medium.
Section 2: Coding
-----------------
Consist of 2 questions Data structure & Algorithms. The total duration of this section was 60 minutes. The level of Questions varies from Cakewalk to Simple, took me 15 mins to code both the questions.
Day 2:
======
Round 1: TPS-1 (Technical Phone Screen-1)
-----------------------------------------
The interview was taken by one of the software develo...
Easy-Medium to Hard. the interviewer is more interested in how well you are
explaining your, and algorithms. The level of question is from Easy-Medium to Hard. the
interviewer is more
110.
dp on a functional graph hello. I have noticed after solving a few problems that there is little to no documentation on this topic, thus, I have decided to write a short blog. this is my first educational blog so please excuse me if there are errors.
note that this is simply an extension of dp on a tree, so it is strongly recommended you study dp on a tree before reading this blog.
firstly, a functional graph is defined as a directed graph where each vertices has exactly one outgoing edge. a key feature of these graphs is that in a connected functional graph, there is always one and only one cycle present. a proof is attached [here](https://math.stackexchange.com/questions/1110332/prove-that-a-graph-with-the-same-number-of-edges-and-vertices-contains-one-cycle). this is crucial for our dp later.
now, let us find an [example problem](https://dmoj.ca/problem/mcco19c2d2p3) for this topic. this problem can be summarized as the following:
Given $n$ people, person $i$ can donate $a_i$ but will not donat...
strongly recommended you study dp on a tree before reading this blog. firstly,
a functional graph is
111.
Blue Hello Codeforces, I am a 15 year old high school student that works hard to improve, after reaching Cyan with 4 months of practice, going on for another 2 months without much improvement and a 2.5 month break, I have just reached Expert after around 9 months. I would like to learn what difficulty range I should study from and what resources would be most beneficial in your opinion. Thank you in advance.
Hello Codeforces, I am a 15 year old high school student that works hard to
improve, after reaching
112.
Psychology for programmers I I always wanted to write article about what I have learned in psychology, and how it relates to programming. It was hard to come up with single article, so I decided that I will write multiple unrelated blogs.
The first post is about **Rating Anxiety**, there have been no scientific studies about this phenomena to my knowledge, but from self-reports of competition programmers, I conclude it exists, and I think a lot coders develop it to certain degree and certain peronalities are more prone for the developement.
Rating anxiety(RA) is when you feel bad about losing rating(TopCoder or CodeForces) and as a consequence of that you either **skip competition** or are nervous and under pressure because of that. In practice this pressure leads to poor performance(thrugh means I will describe in other post), and individual might gain better results if he gets rid of rating anxiety. If your in-contest and ot-contest performance differs somehow, it might be sign of RA. If you feel intese jo...
programming. It was hard to come up with single article, so I decided that I
will write multiple
113.
The Explanation Dilemma Hello Codeforces!
Lately, I’ve become deeply immersed in the world of competitive programming. For me, at least, this has meant a commitment to studying every aspect of it in depth, with the goal of “learning it the right way.” Like many others, I began with the basics—identifying which problems to tackle, figuring out how to practice effectively, and learning how to keep my motivation up during the inevitable struggles. I grappled with questions like whether or not to read editorials. But as I delved deeper, I found myself contemplating broader questions: **How do we truly learn?** And perhaps more importantly, **how do we process and retain information** when we’re trying to master something as intricate as competitive programming?
Like any curious person, I dove headfirst into this exploration, and I was surprised by the sheer volume of posts on this plataform that touch on this subject. There are masters who have ventured into the psychological depths, crafting entire article...
was hit hard by a similar realization: many editorials, algorithms, and data
structures were difficult
114.
Yandex.Algorithm Finals <img src="http://img-fotki.yandex.ru/get/5111/14594669.1/0_7da5c_affb50ad_L.jpg" style="float:right;width:250px;margin:0.5em;">
<p>Hi everybody!</p>
<p>Yandex.Algorithm finalists were gathering in Dolgoprudny... Everybody in their own unique way :)</p>
<p>
<a class="rated-user user-red" href="http://codeforces.me/profile/dzhulgakov" title="General dzhulgakov">dzhulgakov</a>, <a class="rated-user user-red" href="http://codeforces.me/profile/pieguy" title="Lieutenant colonel pieguy">pieguy</a>, <a class="rated-user user-red" href="http://codeforces.me/profile/levlam" title="Lieutenant colonel levlam">levlam</a> and <a class="rated-user user-red" href="http://codeforces.me/profile/Progger" title="Colonel Progger">Progger</a> turned out to be the most organized and arrived at the start of the <a href="it-edu.fizteh.ru/en">Summer School</a>. They've already socialized with other participants and began solving and competing in the practical bioinformatics problem using ...
Announcement of Yandex.Algorithm 2011: Finals
115.
but their hard work over ed when difficult and awkward, but their hard work over the years of sweat is hard to describe.The past two years, with the youth soccer community on Pill concern the improvement of the degree of attention, the local youth football development has been greatly improved. 2011 onwards, Pill campus football special funds included in<a href="http://www.freeasicscheap.co.uk/nike-free-run-2-c-26.html">nike free run 2 sale</a>
the budget, funded by $ 100,000 per year. It is understood that local authorities have views on further strengthening the implementation of the work to form youth football discussion paper, which proposed the establishment of Zhidan county football management, the preparation of 10 people, a substantial increase in the intensity of football funds invested, while building covers an area of 100 acres Comprehensive training base, each school had at least one sentinel professional football teachers. "Our starting point is not the pursuit of results, and the popularity of...
but their hard work over
116.
Palindromic tree: behind the scenes Hi everyone!
As some of you may know, on this summer camp in Petrozavodsk [user:MikhailRubinchik,2014-09-25] presented a new data structure, palindromic tree. I had the honor to participate in the study of the structure for the six months before that, and I want to tell about it now :)
[cut]<br>
But firstly a brief explanation. If you alredy know basic ideas of the structure, you may go to the <a href="#inter">interest part</a>. Let's to each palindrome assign corresponding string equal to its right half, i.e., its radius and the boolean variable indicating its parity. Now let's merge all our radii of subpalindromes of string $S$ in two prefix trees for even and odd lengths separately. Claim: such trie will be $\mathit O(n)$ in memory. Indeed, there can be no more than $n$ distinct subpalindromes in the string, and each node in trie corresponds with only one unique palindrome. Therefore, we have no more than $n + 2$ nodes.
Let's show that such structure can be constructed ...
study of the structure for the six months before that, and I want to tell about
it now :) [cut
117.
Can someone PLEASE help me out for upskilling myself iafter these contests ? Hi ! to whoever is reading this . I know this is another post crying out for some help to reach Pupil or Grandmaster but please , I really need some guidance . I had been practising CP from last 1.5 years on various platforms ( CP , not DSA or core concepts ) and initially I could solve Div 2A , 2B in half and hour and 2C after the Contest :( but I was never admant to reach an appreciable level on the platform.
But , SInce last 20-30 days , I have been toiling hard and practising and studying DSA and all the core concepts of CP on various platforms , solving problems , reading solutions and again repeating the cycle and this time , after a very large gap , I decided to again take the challenge and reach atleast reach green in 2-3 Contests ( too much overconfidence ) but , to my shock , I rarely cross Div 2A these days and Div 2B also seems undoable . I don't know what went wrong in that large gap .
SO , this is just a request if some experienced people can guide me — h...
on the platform. But , SInce last 20-30 days , I have been toiling hard and
practising and, But , SInce last 20-30 days , I have been toiling hard and practising and
studying DSA and all
118.
The Case for Fixed Contest Days on Codeforces First and foremost, a huge thank you to the creators and team behind Codeforces for providing such an incredible platform. Your hard work has made competitive programming accessible and engaging for programmers around the world. However, there’s one enhancement that could make Codeforces even better: fixed contest days.
**Predictable Scheduling**
Imagine if contests were held on the same day every week—say, every Saturday. This regularity would allow participants to plan their practice and participation with ease. No more uncertainty or scrambling to fit contests into unpredictable schedules. A fixed day each week means you can integrate these events into your routine seamlessly.
**Boosting Participation**
A predictable schedule encourages more consistent participation. Knowing exactly when contests will take place helps you set aside time to prepare and compete. This could lead to increased engagement and a more vibrant community. Regular contests could become a weekly hig...
an incredible platform. Your hard work has made competitive programming
accessible and engaging for
119.
How can I qualify to ACM ICPC World Finals 2018 being a sabbatist? I'm a brazilian student who has been training Algorithms for some years. I'm a seventh day adventist, religion that keeps the Sabbath holy. As a consequence of this I can't participate in the Latin America regional phase at all, due to the timezone.
This is my last chance to go to ACM ICPC World Finals and it will be very difficult to my team to qualify without me. I'm not genious, but I have studied hard to do this competition. What should I do?
Thanks in advance!
studied hard to do this competition. What should I do?
120.
Is IOI a pay-to-win game? I would refrain from mentioning any specific examples because this isn't the point of this blog.
Let's consider this situation, Alice and Bob want to study for an exam. Alice will study on his own, may use the internet to look for resources if there's any. On the other side, Bob will be taught and guided by the world's best teacher who has 50+ years of experience and he is the one who will be writing the exam. Both, Alice and Bob, will do their hardest and study for the exam, but could we say that this situation is fair for Alice? Bob has essentially worked hard, but Alice did too, he just didn't have the resources and the personalized guidance that Bob got.
Many countries spend thousands on IOI camps (and on Olympiads in general). That forced the gap between poor and rich countries. Of course, you have countries that rely on talented students and don't care to train them. However, some care more about their students and do more camps and invest in their students. The point is, a...
Let's consider this situation, Alice and Bob want to study for an exam. Alice
willstudy on his own
121.
Quadratic binary energy function minimisations by Flow ## Motivations
I tried to read [https://codeforces.me/blog/entry/148438](https://codeforces.me/blog/entry/148438) and failed. It contains a lot of extra explanations and intuition that I either already knew or could reconstruct immediately. That is not inherently bad, but for me personally it made the key ideas harder to see. (I think most contestants would not struggle with visualising binary logical relations...)
As I asked around (and with help from LLMs), it became clear that the underlying structure is the Kolmogorov–Zabih characterization of which quadratic binary energies are solvable via a single max-flow.
This blog is essentially a reweighting of that material: shorter, more “algebraic”, and aimed at people who are already comfortable with max-flow / min-cut and with abstracting away implementation details. This blog is also just essentially an extremely long comment that is too long to fit in comment section.
## Declarations
While writing this, I did **not**...
**: * Study the original Kolmogorov–Zabih proof in detail beyond a surface
understanding: [https
122.
How does IT work in Iran. Part 1 I took this chance being in Tehran to learn more about professional life of an IT specialist in Iran. This path actually starts in the school, continues at the university followed by a professional career.
Here is the first part of my research, it is an interview with Mr. Ali Ghadiri, the founder and CEO of Bayan. Being not only an IT-entrepreneur, but also serving as a school teacher for over 10 years, he provided information on educational system of Iran as well as about job situation.
Education
---------
**How is the educational system organized in Iran in general? E. g., does one have to pay for school or university?**
Ali Ghadiri: Both paid and free-of-charge models co-exist.
The best schools, especially high schools, are not free. Besides entirely private schools, there are semi-government ones, where you have to pass entrance exams. They are called “sampad” and exist in many cities in Iran, in Tehran there are about 10 sampads for boys and 10 for girls _(Comment ...
universities are the government ones, where students don’t have to pay. In
order tostudy there, you have to
123.
What does the State Space of a BFS means? Recently i tried to solve the [Amazing Robots](https://ioinformatics.org/files/ioi2003problem5.pdf) task in IOI 2003.My first Idea was to run dijsktra while updating weights by calculating the position of guards. As we cannot wait in a position without a command this won't work. After that i have no idea how to solve this.
I googled for a solution and this is the only one i found from [here](https://www.iarcs.org.in/inoi/online-study-material/problems/amazing-robots-soln.php#solution) .
~~~~~
Do a BFS on the state space.
Naive state space is
Position of robots in each grid.
Position of each guard.
This is too large (state space is 400 × 400 × ....).
Instead, compute the guards' positions as a function of time. In this case, we need to maintain:
Position of robots in each grid.
Current time T.
State space is still 400 × 400 × N, where N is the number of steps till they get out, which may become too large.
Observe that the guards' beats are of length 2, 3 or ...
](https://www.iarcs.org.in/inoi/online-study
-material/problems/amazing-robots-soln.php#solution
124.
Convolution, In the Perspective of 3-Dimensional Tensors Hello everyone!
Convolution is perhaps the first class of algorithms that one encounters in competitive programming requiring algebraic knowledge. There are many types of convolutions that we are interested in, including:
- **Sequential convolution** (i.e., polynomial multiplication),
- **XOR convolution**,
- **AND/OR convolution**,
- **GCD/LCM convolution**,
- **Subset convolution**, and others.
One of the most well-known ways to understand fast algorithms for these convolutions is through their associated algebraic structures. These algebraic structures can often be decomposed using the Chinese Remainder Theorem (CRT) into simpler components, i.e., direct products. For instance, in the case of XOR convolution, the algebraic structure arises from the computation rules of the group algebra:
$$
R[\mathbb Z_2^n]\colon \left(\sum_{g\in \mathbb Z_2^n} a_g g\right) \left(\sum_{g\in \mathbb Z_2^n} b_g g\right) = \left(\sum_{g,h\in \mathbb Z_2^n} a_g b_h (g+h) \right),
$$...
no longer hold, and determining the tensor rank becomes an NP-hard problem.
Tensor rank serves as
125.
Is GM in 2–2.5 years realistic? (Current rating: 1036, Aiming for IOI Gold ) Hi everyone,
I recently started taking competitive programming very seriously. I don’t come from a strong olympiad or elite math background, but I am extremely determined to change my life through focused hard work.
My question is simple but very important to me:
Is it realistically possible to reach Codeforces Grandmaster in 2 to 2.5 years?As I have only 3 years and some months to take preparation for IOI.
I am ready to:
Practice 6–10 hours a day if needed
Follow a strict learning plan
Compete in every contest
Study editorials deeply
Track my weaknesses honestly
But before I fully commit my life to this goal, I want brutally honest feedback from experienced competitive programmers.
What I want to know:
How fast do top improvers usually gain rating?
What kind of background do most GMs have?
How many people actually make it compared to how many try?
What mistakes should I absolutely avoid from day one?
Please don’t sugarcoat the answer.
I...
focused hard work. My question is simple but very important to me: Is it
realistically
126.
900 rated problems so hard Hey guys, I just started CP. I am able to solve 800 rated problems very easily but find 900 rated problems hard(especially number theory or math problems). I am currently in 8th grade and studying algebra 1. I am curious if the lack of my high school math skill is the reason solving 900 rated problems very hard.
900 rated problems so hard, problems hard(especially number theory or math problems). I am currently in
8th grade and studying
127.
Codeforces Round 987 (Div. 2) Editorial <spoiler summary="A little backstory about the round (ACGN)">The Highschool CPers (HSCP) Discord server was created in April 2022 by [user:pwned,2024-11-14], which over time grew into a close-knit community of highschool competitive programmers. I joined in the same month of its creation, and in the next month I approached [user:pwned,2024-11-14] about the possibility of setting a contest. Thus the HSCP round concept was born.
Over the next month or so, the initial problems were born; the current problems A and F were produced in June-July 2022. We had several problem ideas by then, enough to set a div.2 round. However, as I was going to be busy in my 5th year of high school, and may not be that responsive to coordinators, the contest was in the ownership of [user:pwned,2024-11-14], who needed to wait until he reached master in order to propose the set on Codeforces.
However, this step took almost 1.5 years as he would stay at candidate master for 57 consecutive contests, eve...
above. The result is as follows and can be hard-coded:
$\mathtt{1~3~3~4~4~5~5~6~6~1~2~7~7~8~8~9~9
Tutorial of Codeforces Round 987 (Div. 2)
128.
July, 6 — 13, we welcome students to Discover Vladivostok 2019 boot camp Dear Codeforces!
We invite you and your team to take part in programming camp **Discover Vladivostok by Moscow Workshops ICPC** in the Far East Federal University Campus from **6th to 13th of July 2019**. Waiting for talented competitive programmers (and future competitive programmers too!) Official language is English.
We invite you not only to study, but also to admire Vladivostok, the Pacific gate of Russia.
Citizens of 18 countries can apply for a **free electronic visa** and stay in Vladivostok for 8 days starting from the date on entry. It means that students from Algeria, Bahrain, Brunei, India, Iran, Qatar, The People's Republic of China, The Democratic People's Republic of Korea, Kuwait, Morocco, Mexico, The United Arab Emirates, Oman, Saudi Arabia, Singapore, Tunisia, Turkey and Japan have an opportunity to proceed 10-minutes online registration, and then come to Russia. And they are not requ...
) We invite you not only to study, but also to admire Vladivostok, the Pacific
gate of Russia
129.
Performance Ratings vs Ratings of Solvable Problems for the Recent GPT Models The GPT models have made great advancements in competitive programming recently. I saw from [user:Qingyu,2024-12-21]'s [blog](https://codeforces.net/blog/entry/137534) earlier that the new o3 model claims to achieve a 2727 performance rating.
However, I'm slightly uncertain of how this 'rating achieved' should be interpreted. There is very little detail publicly available on how the performance ratings are computed. The only available detail I could find regarding their benchmark methodology is the following quote from the ['reasoning with LLMs' blog](https://openai.com/index/learning-to-reason-with-llms/):
> Finally, we simulated competitive programming contests hosted by Codeforces to demonstrate this model’s coding skill. Our evaluations closely matched competition rules and allowed for 10 submissions.
This does not really offer any detailed computation methods. Given the limited details, I'm hypothesising that the LLM doesn't need to solve problems anywhere close to the 270...
. To study the above, I've collated some data from the recent Division 1
contests. For each contest
130.
Competitive Programming PyPy 3-64 Template for Beginners Hello Dear Friends,
I hope you and your families all are doing well during these tough times. Being a beginner in CP I found it very hard to come up with faster solutions in Python (the only language I am good at) and recently while going through some Git Repositories I found out a Python (PyPy) template for Competitive Programming. But since that Repo was outdated, I decided to make my own version of the template after doing some study on the previous template. So here I am presenting to you all my version of the Python Template which runs fine in all versions of Python in both Codechef and Codeforces. I have uploaded 3 templates and some boiler plate code to save time in Contests.Hope you guys find it helpful.
Repository : https://github.com/CyberkidAdithya/CompetitivePython
I hope my repository will be helpful especially for beginners (1 star and 2 star coders) who are just entering world of CP. Feel free to play with it and make tweaks as per your needs. :) And do let me kn...
. Being a beginner in CP I found it very hard to come up with faster solutions
in Python (the only
131.
Codeforces Round #331 Editorial [Problem A](http://codeforces.me/contest/596/problem/A)
==================
It is a necessary and sufficient condition that we have exactly 2 distinct values for $x$ and $y$. If we have less than 2 distinct values for any variable, then there is no way to know the length of that dimension. If there are at least 3 distinct values for any variable, then that means more than 3 vertices lie on that dimension, which cannot happen since there can be at most 2 vertices in a line segment. The area, if it can be found, is just the difference of values of the $x$ coordinates times the difference of values of the $y$ coordinates.
**Complexity**: $O(1)$
**Code**: [Solution](http://codeforces.me/contest/596/submission/14290507)
[Problem B](http://codeforces.me/contest/596/problem/B)
==================
No matter what, we make $|b_1|$ operations to make $a_1$ equal to $b_1$. Once this is done, $a_2, a_3, \cdots a_n = b_1$. Then no matter what, we must make $|b_2 - b_1|$ operations ...
/Representation_theory_of_the_symmetric_group)). Essential objects in the study
of $S_n$ are Young diagrams and standard
Tutorial of Codeforces Round 331 (Div. 2)
132.
How can I quickly improve my level? Please give me some advice on how you did it. Hello, everyone! I am a ninth-grade student, I am involved in sports programming, and I want to achieve success in this field, but I have some problems.
Basically, I need to work very hard, but my studies take up a lot of my time. I would like to ask you how you did sports programming while studying. How did you get the most out of the tasks? Please share your overall experience in sports programming and give some advice based on your experience.
**Thank you, everyone!**
Translated with DeepL.com (free version)
achieve success in this field, but I have some problems. Basically, I need to
work veryhard, but my, Basically, I need to work very hard, but my studies take up a lot of my time. I
would like to ask
133.
A Christmas Gift for CP: CodeMentor ## CodeMentor: Your AI-Powered Companion for Competitive Programming
Hi Codeforces!
I'm excited to share **CodeMentor** — a Chrome extension I built that gives you progressive AI hints and explanations when you're stuck on problems, without spoiling the solution. It's designed to help you learn and grow, whether you're practicing for contests or preparing for interviews.
## What It Does
**For Codeforces & CodeChef (Competitive Programming):** Get progressive hints to improve your CP skills without spoiling solutions. Perfect for when you're stuck during practice or want to understand a problem better after a contest.
**For LeetCode (Interview Preparation):** Get detailed explanations and hints to understand problems better for technical interviews. Learn problem-solving patterns and approaches that interviewers look for.
---
## Features That Will Help You
### Progressive AI Hints & Explanations
**The Problem:** You're stuck on a problem. You've been sta...
level? Too easy? Too hard? - **Suggest features** — What else would make your
competitive
134.
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'd have a fighting chance at taking down the best. But problems A and B were
unusuallyhard this
135.
Advice about solving probabilities and expectation problems Hi,
I'm trying to improve myself in solving problems about probabilities and mathematical
expectation, but I find most of problems hard to me especially those problems where
I need to find the expected value, because I feel that every problem needs a way
to think about that is different from the other problems, and trying to apply
the formal definition of the expected value is always useless.
So, could you please provide me with a way to improve myself or some stuff to study from ?
expectation, but I find most of problems hard to me especially those problems
where I need to find
136.
Please help me with my problem Hello, my name is Suhana and my life became a nightmare. I was a student at Indian Institute of Technology Hyderabad, during that time I was studying hard, ignoring all parties and cf rounds. Just after graduation my boyfriend Kumar and I have decided to go to the nearest pub and celebrate my successful graduation. This was a huge mistake, I remember how we entered the pub and don't remember anything that happened after. Nine months later I gave birth to my son Rishabh. Kumar wasn't ready for kids, so he left me alnoe with my baby.
In order to raise a child I need money badly. I have diploma in Computer Science, but my CF rating is poor (I dedicated myself to studies and had no time for CF). As you may already know, having high CF rank in order to get a job in India is a must. Clearly, I don't have time for participating in CF rounds, but I need the job. I would be so thankful, if someone could sell me his/her yellow profile (or better). I am ready to give 25000 INR (around 350 USD...
Technology Hyderabad, during that time I was studying hard, ignoring all
parties and cf rounds. Just
137.
How to approach Square Root Decomposition Problems? Hi everyone,
Recently I came across a problem [RACETIME](http://www.spoj.com/problems/RACETIME/) on SPOJ.
After trying hard for the problem when I couldn't make a progress I searched internet for a solution.
Discussions on various forums talked about the technique of **Square Root Decomposition**.
So I studied about this technique from [here](http://www.infoarena.ro/blog/square-root-trick).
I looked for various other problems also which used this technique like [1](http://codeforces.me/contest/86/problem/D),[2](http://codeforces.me/gym/100255),[3](http://acmp.ru/?main=task&id_task=647) and [4](http://www.codechef.com/problems/FNCS)
But after going through all of them my question is
**What thinking process does one undergo before coming up to the conclusion that a particular problem can be solved using Square Root Decomposition?**
Sometimes they even divide the queries into _sqrt N_ buckets and then solve them?How does that one even think that.
I have searched...
/) on SPOJ. After trying hard for the problem when I couldn't make a progress I
searched internet for
138.
HARD PROBLEM FOR ME Hello, I recently started studying algorithms in computational geometry, I seem to have problems with the following computational geometry problem, I have searched long and hard but still cant find a solution: it goes: given n points, find the triplicate whose angle is close to 90 as possible. any suggestions will be appreciated.
HARD PROBLEM FOR ME, with the following computational geometry problem, I have searched long and
hard but still cant find a
139.
Let’s Stop AI Cheating — A Simple Start for Codeforces Contests on Codeforces don’t feel the same anymore. Many of us spend weeks learning, solving, and struggling, while others just open AI tools and take unfair ranks. This makes honest coders feel ignored, and if this keeps going, real competition will slowly die. The winners won’t be the best programmers anymore, just the best at talking to AI tools.
My proposal is simple, and just a first version: Codeforces could create an official browser extension. To join a contest, you must turn it on during the contest. It blocks AI pages and cheating tools. I know it’s not a perfect solution, but it’s a fair first step. It makes cheating harder and protects those who want to compete honestly.
An extension works because site blockers already exist. If Codeforces builds its own version, the community can improve and update it. Start small: block obvious AI tools. Later, combine it with copy-paste checks and stronger measures.
To everyone who does not cheat: you are not alone. Please don’t...
140.
IQ is Pure COPE, Here's Why (Useful CP and Life Information #5?) Background
------------------
On CF I think you can tend to see people attributing good rating to IQ. This is often associated with hopelessness when people are stuck in gray/green.
I think it's the perfect cope — it's the easiest thing to say that completely explains why you're 1100 and your friend is orange, and, bonus, if anyone tries to prove you wrong, you can just claim that they are privileged and intelligent.
You may think I am 2000 and thus out of touch to be able to comment on this topic, which _may_ be true. However, I was also once a noob who got 28/1000 on a USACO silver round. And I was pretty overweight as a kid and sucked at sports and always thought of myself as not having the genetics to be an athlete, but [I now hold the squat, bench, and deadlift 18-and-under state records in my powerlifting federation](https://pa.liftingdatabase.com/records-default?recordtypeid=72&categoryid=603&weightclassid=5). (Probably not for long though lol)
A lot of this i...
Milkshake" study, hormonal hunger responses to food were affected by whether
the milkshake was
141.
**Smart Practice Guide for Competitive Programming** **Salam everyone,**
This blog is a **simple and practical guide** on how to practice competitive programming, how to learn new algorithms, when to read others’ code, and how to prepare for **NOI / OI-style contests**.
Everything here is based on **practice ideas**, written in **easy English**, with **no extra theory**.
---
## 1. How to Learn a New Algorithm
**Do NOT learn algorithms first. Learn them when you need them.**
### Correct way to learn an algorithm:
1. Pick a problem.
2. Think seriously for about **15 minutes**.
3. If you are stuck, read the **editorial**.
4. If the editorial uses a new algorithm or idea you don’t know:
* Read **one article** about it (USACO Guide, CP-Algorithms, or CF blog).
* Understand the idea, not memorise it.
* Implement it **in that same problem**.
5. Move on to the next problem.
### Why this works:
* You learn the algorithm **in context**.
* You remember **when to use it**, not just what it is.
* Important...
. * Important algorithms appear again naturally in future problems. ### Do NOT:
*Study algorithms by
142.
Studied C++ for Four Months I studied cpp for four months. I've been a speacialist! But I've not solved a C in codeforces contest(Div2). I must stedied harder and harder. My goal is to become an expert.
143.
If you ask me how to improve your algorithm competition skill, I will give you the link of this blog. In recent one year, I don't know why, but there are many people send messages to me for asking similar problems. So I decide to create this blog.
In the beginning, I must to say, you may feel disappointed after reading this blog. Because I don't have any special tips. My study method waste many many time.
There are some basic points I think you have known.
Practice, practice, and practice. I take so many time to think and solve problems. I think I do it 5 hours in a day on average.
Make friends with many awesome people. I know many awesome people. For example, arosusti, kelvin, peter50216(0O0o00OO0Oo0o0Oo), seanwu, Shik, takaramono, tmt514, ... If I have some problems that I can't solve in few weeks, I can almost get solution from my friends.
Then I say what I do for training myself.
When I do problems. There are two possible order for choosing problem.
Start from most people solved one.
Solve consecutive Numbers of problems and try to solve all of...
disappointed after reading this blog. Because I don't have any special tips. My
study method waste
144.
Surprise! [My surprise in the latest Surprise Language Round #8](http://codeforces.me/blog/entry/45454?#comment-300476) got me thinking. What is a surprise? Everybody is surprised by different things. If someone is new to competitive programming, there is an easy way to surprise him: just let him multiply two numbers. The constraints don't even have to be 10^9, 10^5 is enough:) But surprising more experienced coders is much harder.
I like the problems that have some element of surprise or anything non-standard. The problems that somehow force the contestant to dig deeper. Something more than just reading the problem statement and converting it to DP. In the regular rounds most often the surprise comes from the missing knowledge about the particular algorithm. If I didn't know about the algorithm, I can google it after the contest, study it, add to personal library and wait for the next contest with similar problem. How can a problem statement be even more surprising?
There is a link betw...
algorithm, I can google it after the contest, study it, add to personal
library and wait for the next
145.
On how to practice Introduction
============
Hello, CodeForces! Firstly, I would like to thank Mike Mirzayanov, as well other organizers of competitive programming events, and their sponsors for ability to freely (or at least cheaply) participate in contests (including onsite ones) and sometimes even win prizes. I have some -- yet not very outstanding -- experience in the field, yet have never really contributed something to the community. Today I would like to break such silence and write my first blog post with humble opinion on standard topic: that is, on how it is optimal to practice competitive programming. I understand that most people will not agree with me, but at least some will listen due to my rating exceeding theirs.
Context
=======
In long distant year of 2018 when I started to compete, I had quite intense desire: to learn how to solve problems, or at least so I formulated my intention. Despite achieving some success in the field of competitive programming I have not been satisfied,...
there even exist singular method to solve problems? Although it is hard to
disprove existence of
146.
cGPA vs Programming Contest If a person loves programming too much and can never concentrate on academic studies which one he should prefer mostly?Programming or cGPA?I'm asking this because i worked too hard and spent too much time in coding in the last few months but didn't get the desired result!I started programming too late.It's almost 2 years.And i started participating in contests 8/9 months ago.So it's taking too much time for me to fill the gaps.I just have 2 years left of my graduation.And my cGPA is going down semester by semester.So i just have two choices left.Either i have to continue spending most of my times in coding to become more skilled or i have to give much time for academic courses to make my cGPA higher.But i really prefer programming over everything.Though my performences are not that much good till now but i want to give my 100% for it to become a very skilled coder before next year.I'm just frustrated and confused!I would really appreciate some suggestions!
should prefer mostly?Programming or cGPA?I'm asking this because i worked too
hard and spent too much
147.
How can I improve my rank... Hi, I'm Chinese student looking for some tips for improvement in my OI studies. I have been working hard in this subject and although I believe my efforts are not in vain, my performance in school contests has been consistently poor. I feel discouraged with my low ranking. Can you provide me with some suggestions or techniques that can help me improve my performance within the next two months? Thank you very much! Please forgive me for any mistakes in my English. I am using ChatGpt to assist me in amending it.
working hard in this subject and although I believe my efforts are not in
vain, my performance in school
148.
I need a teacher ... I got stuck at this [problem](http://usaco.org/index.php?page=viewproblem2&cpid=943) while trying to learn sweep line technique. I've read [the editorial for that problem](http://usaco.org/current/data/sol_cowjump_silver_open19.html) and got seriously confused at the "y coordinate for a segment" part. Like ... how can we compare the y coordinate when a segment consist of two points ? (Apparently I think it has something to do with sorting points by increasing x coordinate, but can't figure out why ...). Also why do we only check for intersection with the "above" segment in the `active` set when we first meet the beginning of a segment, but check for both the "above" and "below" when we meet a segment's end ? Please explain all of my question in details if possible.
P/s : Remember that I have 2 questions ...
Edit:
There's no respond ... At this point let me ask something straight, and possibly easier : Do you know any red or generally high ranked people that are willing to answer...
get in the way of one of my sleep phase. But as I study more, there's one
clear disadvantage : I have, ranked contest, as it always get in the way of one of my sleep phase. But as I
study more, there's one
149.
Suggest Implementation-heavy problems please. My implementation skills are so bad it needs to be studied. I struggle to implement even the simplest solutions, even though I have the right idea in my mind. Please tell some really hard/heavy implementation problems that I can practice to get good. Thanks!
simplest solutions, even though I have the right idea in my mind. Please tell
some reallyhard/heavy
150.
Tourist Gave Me The Challenge Of My Life I met tourist at the training camp last night. He looked right at me, a focused intensity in his eyes I recognized instantly. We skipped the small talk. He grabbed his laptop and led me to the study lounge. Against the whiteboard in the corner, he started sketching a problem. Fast, complex, demanding. He pushed me to find the optimal complexity. His hand went straight for the keyboard, typing the first few lines of a template quickly. I felt the pressure as I looked at the constraints. He grinned. We rushed back to the main lab nearby. Keyboards started clicking as soon as the door shut. His logic was amazing. Strong and efficient. I sat down and started debugging his complex segment tree. It felt intricate and clever. He groaned as he realized he had a memory leak, grabbing his hair in frustration. Then he pulled me up, spinning the monitor around. He pushed me to handle the edge cases on his rug-covered workspace. He optimized his loops and functions quickly. He teased the solution w...
eyes I recognized instantly. We skipped the small talk. He grabbed his laptop
and led me to thestudy
151.
Relation between data structure and design pattern [Design Pattern 101](https://codeburst.io/design-patterns-101-9fe18d5a1bd9?source=friends_link&sk=e0a82f4a24100530f9c079a71fe5a706)
I just read this article, liked it very much. I think for begineers like mine, it's a good read.
Here is a summary: For more detail you can check the link.
The design pattern is one of the most important but feared aspects of software engineering, especially for people who are new to the topic. The main reason for this was that the terms which are used in the patterns are pretty hard to understand at first. Besides this, it can be hard to know which books should you read or which websites provide better guidance around the concept, so knowing how to progress can be tricky.
A design pattern is a solution to a commonly occurring software development problem. Every design pattern has a structured template.
Consider a design pattern is the same as a well-known Algorithm with structure. As new computer science students become more used to data struct...
patterns are pretty hard to understand at first. Besides this, it can be hard
to know which books
152.
The SIMPLEST FFT explanation EVER! You know FFT can be used to solve a lot of hard problems that require multiplying two polynomials, for example yesterday's hardest problem. Also many string matching problems can be transformed into an analogous polynomial problem and be solved using FFT.
Have you ever tried studying FFT but gave up because it was too mathy and difficult to understand?
Well, that won't happen anymore! Because a kind programmer who goes by the handle of RiAst decided to write a tutorial so that we, the ones who don't know much math, can finally understand and implement FFT. Here's the **Ultimate Guide** to understanding FFT once and for all!
Without furthed ado, here's the link to said glorious tutorial: [Simple FFT Tutorial by RiAst](https://www.youtube.com/watch?v=dQw4w9WgXcQ)
You know FFT can be used to solve a lot of hard problems that require
multiplying two polynomials
153.
how become a newbie? How to become a newbie?To do this, you need to work very hard and it's not as easy as it seems! At the beginning it seems that this is impossible, but do not give up!After many hard and difficult training sessions, you can become a newbie!I advise you to study the programming database and devote an average of 25 hours a day to programming and solving problems of IOI, ICPC and many other world-class competitions (very useful
How to become a newbie?To do this, you need to work very hard and it's not as
easy as it seems! At
154.
TCO 2011 as seen by a blogger, p.2 <a href="http://codeforces.me/blog/entry/2788">Part 1</a>
<br /><br />
My further narration becomes less sequential and consistent than the first part. This is mostly due to the fact that competition rounds themselves are covered in the official blog (not to mention that I haven't followed all of them from start to finish), so I'll focus on the interesting things which were happening between the rounds, after them and sometimes even instead of them :-)
<br /><br />
At the end of July TopCoder Studio ran a <a href="http://studio.topcoder.com/?module=ViewContestDetails&ct=30022930">contest</a> to get some ideas of how to entertain people at the onsites. The voting for the ideas had a very poor interface (I wonder whether there was a single person who has read all the ideas before voting?), but still it allowed to choose four ideas:
<br />
[cut]
<br />
1. Football game. Originally it was supposed to be a real football game, but it turned out to be tricky implementation-wise, so it was...
tasks (it's hard to believe, but none of them required even going to the
beach, not to mention the
155.
A Recap of My First Year in CodeForces Hello all on Codeforces!
------------------
It’s been just over a full year since I created my Codeforces account. Since then a lot has happened on my Codeforces journey so far. With everything that’s happened I want to look back at how I got to my current point, share what I learned in the process, recap some of my best moments, and laugh at whatever I was thinking on a few of these contests, because a lot happened. The only issue is that there’s no way I’m going to detail all **60** contests I took part in 2022. Instead I’ve chosen to “award” the 9 most memorable contests, wheter it be because I did exceedingly well or self destructed in almost hilarious fashion.
A few notes before I begin: No full solutions for any problems are shown in this post but there are code snippets and discussions that are spoilers for these problems. I apologize in advance.
### First Contest — [Hello 2022](https://codeforces.me/contest/1621)
This was the first contest held in 2022, ...
about 4 terms of Computer Science study at SFU, a few offhand miniprojects, a
solid math foundation
156.
A blog on the Sprague-Grundy Theorem So, I ended up making a talk on Sprague-Grundy as part of a club at my school, and thought that the denizens of codeforces would appreciate it. As follows is roughly what was on the handout, which goes over Sprague-Grundy along with the application of its theory to Nim. As this is my first blog post on Codeforces, please do let me know if there are any mistakes in formatting.
I hope you find this interesting, as writing and explaining this helped me understand how to apply it to problems. This handout was written as more math-oriented, so it may be a bit heavy. The exercises are left unsolved, as they are intended to be worked through by the reader.
If you just want to get to what the Sprague-Grundy is defined as, search for "The Sprague-Grundy function of a game" after reading how games were defined.
Way too much theory
=============================
A necessary definition of games
-------------------------------
For this talk, a game will be a two-player sequential game o...
157.
Help me! Hello everybody!
I'm studying DP at this moment, and i'm a little bit lost.. I know the basics DP's,but in the hardests i'm not very good. Can anyone help me saying good DP exercises like (DP+bitmask) or some hard DP's.Thank you!
+bitmask) or some hard DP's.Thank you!
158.
How to be better at coding ? Hello CODEFORCES!
I'm finding a problem with improving(I want to higher my rate) while keeping up with my life(studying ,sport , hanging out...).
I started to use USACO GUIDE , I know It's helpful ,but I sometimes find It a little hard .
Sooo... if anyone got any ideas to tell me how they improve cuz I'm still a Newbie :(
------------------
,but I sometimes find It a little hard . Sooo... if anyone got any ideas to
tell me how they
159.
Meritocracy, Intelligence, and the Uncomfortable Question at the Heart of Competitive Programming Competitive programming communities are built upon a deeply appealing idea: that performance is earned. The premise is straightforward. Those who study more, practice more, and persist longer will eventually rise. Ratings, in this view, are not merely measurements of skill but reflections of effort, discipline, and commitment. It is a narrative that resonates because it feels fair. Everyone enters the system under the same rules, and the number beside their name appears, at least on the surface, to reflect what they have achieved.
Yet beneath this narrative lies a question that is rarely discussed directly, perhaps because it is uncomfortable to even phrase correctly. To what extent do ratings reflect improvement over time, and to what extent do they simply reveal what was already there in the first place?
Anyone who has spent enough time in the community has witnessed a pattern that is difficult to ignore. Two participants may begin learning at roughly the same time, use similar...
earned. The premise is straightforward. Those who study more, practice more,
and persist longer will
160.
Some thinking about randomization. ## Introduction
Chinese Version:[Link](https://www.luogu.com.cn/article/gt9xd9oo)
**UPD#1 18.12.25: Fixed relevant typos and rigorousness errors; added the randomization concept in Treap.**
Mention "randomization" and most people's first reaction is probably flipping a coin to bet on `YES` or `NO`.
Randomization itself, often seen as an "unorthodox method" (or "dark art"), is generally discarded by teachers in standard educational institutions and is rarely explained in depth.
However, in reality, the power of randomization is beyond your imagination.
## Magical Randomization
Randomization essentially means shuffling a set of data to make it lose some of its original properties, or to grant it new properties.
So, what’s the use of these so-called new properties? Let’s taste a few problems:
### Example 1: Countering Extreme Data
Suppose you need to implement a sorting algorithm, but you choose the unstable Quick Sort. Suddenly, a mysterious hacker from Code...
hard to hack this way. But similarly, no one has proved this thing is
invincible; it's just that
161.
Scaler Academy: Our side of the story: AMA Hello folks,
My name is Anshuman and I am the co-founder of Scaler Academy and InterviewBit.
I am a competitive coder myself, since 2006, been a part of Codeforces since 2009, when Beta rounds were happening. Been to ACM ICPC World Finals twice. Ex-Facebook where I was one of tech leads on the messages and messenger team.
I believe every company/program gets criticism and it should only be taken constructively. While most of the blogs here on Scaler Academy have been very far from truth, I never came to respond here because it’s hard to reason with anonymous fake accounts.
However, the past few days, these folks have started harassing and abusing current Scaler Academy students and mentors. They created a phishing website clone of ours to steal student credentials. They have bullied anyone who has tried to express their opinion if it was positive towards scaler.
**That, in my dictionary, is online bullying and very unethical.**
Attaching images of students and mentors wh...
, I never came to respond here because it’s hard to reason with anonymous fake
accounts. However
162.
Codeforces Round 979 Editorial Below is a timeline of the changes made to the round from start to finish. I hope this can depict what setting a contest is actually like for aspiring problemsetters. Please give me feedback about this in the comments. What else about the round would you like to know? Was this helpful?
<spoiler summary="Round Timeline">
To denote problems, I will use quotes to denote the number of problems proposed for that postion so far (e.g. A' represents the first A proposed for the round, A'' represents second A proposed, etc). If the problem is in the final set, then it will be **bolded**. For dates, I will use the american standard notation (mm/dd).
Also, I will not go in detail about why problems were rejected/unused because they might appear in the future.
8/11: [contest:1998] has just concluded and [user:sum,2024-10-18] has shipped himself off to college and won't have time due to <s>attending frat parties</s> his studies. I invite [user:vgoofficial,2024-10-18] to problemset with m...
="Solution (Hard Version)"> Let us find the contribution of $r[i]$, the right
endpoint of $i$-th
Tutorial of Codeforces Round 979 (Div. 2)
163.
Operating Systems Notes If you are struggling with the right track and a 10-min read for Operating systems from beginning to end, you're at the right place. Even I am not sure where to start, but we would figure it and if you are reading this, I have successfully completed these notes or at least am on right track.
Let's start our struggle for OS:
### The Track
I found many resources to learn, let's just list all:
(Galvin Concise PPTs)[https://www.os-book.com/OS9/slide-dir/index.html]: These were great but I felt that these are a little bit too much, so here are the chapters we would do:
1. Processes
2. Threads
3. Process Synchronization
4. CPU Scheduling Algorithms
5. Deadlocks
6. Main memory
7. Virtual memory
8. Virtual Machines
> I am skipping the introduction of OS for now as it was not that important, this is going to be a fast article that works like a last night dose.
<spoiler summary="A simple introduction(May skip if you are already familiar)">
An Operating system is like a...
many processes run simultaneously, we would have a hard time finding the
process containing the error
164.
An awesome list for competitive programming! This is a project I started from late January 2016.
My motive is that: Although there's fantastic information out there, I think they're still spread all over the place. Therefore, in my opinion it would probably be cool if there's an [awesome list](https://github.com/sindresorhus/awesome) for competitive programming! ( *It's now featured on the main list!* )
I'm actively updating the list here: [https://github.com/lnishan/awesome-competitive-programming](https://github.com/lnishan/awesome-competitive-programming)
# Awesome Competitive Programming [](https://github.com/sindresorhus/awesome)
A curated list of awesome `Competitive Programming`, `Algorithm` and `Data Structure` resources.
Created with a view to connecting people to information, this list below contains a complete collection of all the fantastic resources I've collected over the course of my 11...
MAEHARA (@tmaehara) | High-quality implementations of many hard algorithms and
data structures
165.
ICPC Asia West Continent Final Contest 2023 — Problem A and E #### Motivation
A few weeks back I had the opportunity to attend the [ICPC Asia West Continent Finals 2023](https://codedrills.io/contests/icpc-asia-west-continent-final-contest-2023) along with my teammates [user:VS-Codes,2024-04-11] and [user:om_mittal7,2024-04-11], where we encountered the following problems as part of the contest problemset. We weren't able to solve E in contest, and that kept bugging me for quite a while. I was especially motivated to try and prove the claims that we had made in the contest, which proved to be quite a hard challenge.
Finally, when I did manage to cook up solutions with reasonably sound proofs, the underlying ideas and the little observations made along the way felt so elegant that I decided to document it here for future reference, and to share with the community. I hope these ideas turn out to be useful for someone stuck in a similar place as I was.
Looking forward to your thoughts and suggestions!
## [A. Basic Vocabulary](https://cod...
had made in the contest, which proved to be quite a hard challenge. Finally,
when I did manage to
166.
day 3 12:21 on 15/8/25 -> i am attemting SYSTEM design cousors | cplog So today i will do some system designe course from codeWithAryan youtube channal https://codewitharyan.com/system-design/low-level-design -> this course i m finding it very good as per the thinking point of veiw
my weigth right now is 89 Kg i m over weight so thats y my body is not adapting to the hard work.
when ever i am studing i am getting lazy and very sleepy when ever my focus is inceasing my sleepness is incearsing idk what to do
12:25-> i m doing https://www.youtube.com/watch?v=xMNSTBGoGbU&t=35s
13:55 went to sleep after that now i came on 13:55 to study
14:35 -> i did https://www.youtube.com/watch?v=xMNSTBGoGbU&t=35s video and got to know many things -> going eat or lunch
15:24 -> watch some tv and now going to solve some CF queastion
the hard work. when ever i am studing i am getting lazy and very sleepy when
ever my focus is
167.
Rockethon 2014 Editorial In this post you will find the authors' solutions for the problems and subproblems featured in the competition, as well as some bonus questions related to these tasks.
[problem:391A]
--------------
Note that we can consider each maximal sequence of identical characters independently, since there is no way to insert a character and affect more than one such sequence. Also, note that there are multiple ways to correct a single maximal sequence by inserting one character into it: we can either insert a different character somewhere in this sequence and divide it into two sequences of odd length (this is always possible for a sequence of even length), or even just add the same character in any point of this sequence, thus increasing its length by 1 and changing its parity.
Therefore, the answer to the problem is the number of maximal sequences of even length. One can find all such sequences in linear time. A pseudocode of the solution follows:
~~~~~
i = 1
ans = 0
while i ...
subproblem: we are maximizing a sum composed of several components, the only "
hard" part of which is
Tutorial of Rockethon 2014
168.
Last 3 Days: Recursion Finally Stopped Feeling Like Magic Hi everyone!
Over the last few days, I focused almost entirely on **recursion**. Before that, I could sometimes write a recursive function by following a familiar pattern, but I did not always understand *why* it worked or how to discover the recursive idea in a new problem.
Now I have started approaching these problems differently. Instead of writing code immediately or trying to imagine every function call, I first define the meaning of the state.
## What I now do before writing recursion
Before coding, I try to answer four questions:
* what exactly the function should do or return;
* what the simplest possible case is;
* how the answer can be expressed using a smaller problem;
* why every recursive call moves closer to termination.
For example, if a function solves a problem for $n$, the next call usually works with a smaller value such as $n-1$, $n/2$, or another simpler state.
The most important thing is that recursion must not call itself forever. That is ...
study next Over the next few days, I want to practice: * DFS on graphs; * DFS
on two
169.
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...
especially useful for those who are reluctant to study segment trees (I
think). You are given an
170.
Max Flow Implementation #### Overview
In this post I will explain with an example one way to code the Edmonds Karp max flow algorithm to solve a problem.
#### The Problem
The problem we study is Array and Operations http://codeforces.me/problemset/problem/498/C. The basic idea is you have a sequence of numbers and a bunch of special pairs taken from the sequence. For any of the pairs you can divide each number by a common factor greater than 1 and replace the elements in the pair with the result of this division. The question asks what is the maximum number of times you can do this.
#### Converting this to a max flow problem
This section is specific to the problem. You can skip it if you just want to know how to implement Edmonds Karp on a given flow network.
Before we convert this problem to a max flow problem we make some observations. First if we have a pair of numbers the maximum amount of times we can perform the operation described on this pair is equal to the number of prime divisors the p...
flow algorithm to solve a problem. #### The Problem The problem we study is
Array and Operations
171.
Hello 2026 Editorial We'd like to thank you all for participating in the contest, and hope you enjoyed it. Any feedback would be appreciated!
<spoiler summary="Rate The Contest!">
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Great contest
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Good contest
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Average contest
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Bad contest
</spoiler>
## [2183A — Binary Array Game](https://codeforces.me/contest/2183/problem/A)
Idea & Preparation: [user:wangmarui,2025-12-23]
<spoiler summary="Rate The Problem!">
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Good Problem
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Okay Problem
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Bad Problem
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Didn't Solve
</spoiler>
<spoiler summary="Hint 1">
If the sequence $a$ consists entirely of $1$ s, what will Alice do?
</spoiler>
<spoiler summary="Hint 2">
Consider discussing the values of $a_1$ and $a_n$.
</spoiler>
<spoiler summary="Solution">
First, if the entire sequence consists of $1$ s, Alice wins immediately by operating on the whole sequen...
from the constructive proof in D2. ## [2183D2 — Tree Coloring (Hard Version
Tutorial of Hello 2026
172.
Hello , every programmer ! My name is Jacob Chou , and I'm a freshman about algorithm . Last night is the first time I enjoy CF's contest , well it's just a start , I'll be studying harder .
Even my English is bullshit , I also enjoy make friend with everybody who love algorithm . my E-mail is [email protected]
173.
C++ If you want learn C++. Study hard!!!
It's not easy
If you want learn C++. Study hard!!! It's not easy
174.
Good Bye 2024: 2025 is NEAR Editorial Thank you for participating in this round! Problems A and G are authored by [user: Cocoly1990,2024-11-23] and the rest by me.
Currently, I'm not sure if the editorials are fine enough. Please feel free to tell me where I can improve.
<spoiler summary=" Rating Predictions">
| | A | B | C | D | E | F | G | H | I |
| :--------------------------------: | :--: | :---------: | :--: | :----------: | :--: | :--: | :----------: | :--: | :----------: |
| [user:wyrqwq,2024-12-20] | 800 | 1200 | 1400 | 1700 | 1900 | 2500 | [2800, 3300] | 3200 | [800, 3000] |
| [user:Cocoly1990,2024-12-20] | 800 | 1300 | | | | | 3000 | | |
| [user:TheScrasse,2024-12-20] | 800 | 1200 | ? | 1800 | | 2500 | 3000 | 3000 | 3500 |
| [user:LMydd0225,2024-12-20] | 800 | ...
not have to be deterministic) We do not need any hard string algorithm.
Tutorial of Good Bye 2024: 2025 is NEAR
175.
Reusable modular integer for C++ (with static/dynamic moduli) <spoiler summary="A little bit about myself">
This is my first blog post on CF, and is probably a good starting topic for someone of my rating. Technically I'm not a CS, but an engineer who worked professionally as a software developer. CP was uncharted territory to me until recently, though now I find myself studying algorithms and working to improve my math skills so I can have fun solving difficult problems. :)
</spoiler>
So here's what I present: a structure for modular arithmetic operations which is short, reusable across static and dynamic moduli, supports 64-bit moduli and is as efficient as performing the operations manually. It requires the C++17 standard or newer.
### Motivation
For the most part, there's obviously nothing novel about this idea: it was inspired by other blog posts ([63903](https://codeforces.me/blog/entry/63903), [23365](https://codeforces.me/blog/entry/23365)), as well as by various submissions to CF problems. On the other hand, I haven't come a...
these structures: - [1984C2 — Magnitude (Hard
Version)](https://codeforces.me/contest
176.
An awesome list for competitive programming! This is a project I started from late January 2016.
My motive is that: Although there's fantastic information out there, I think they're still spread all over the place. Therefore, in my opinion it would probably be cool if there's an awesome list for competitive programming! ( It's now featured on the main list! )
I'm actively updating the list here: https://github.com/lnishan/awesome-competitive-programming
Awesome Competitive Programming Awesome
A curated list of awesome Competitive Programming, Algorithm and Data Structure resources.
Created with a view to connecting people to information, this list below contains a complete collection of all the fantastic resources I've collected over the course of my 11-year competitive programming career. I hope you'll find it useful :)
What is competitive programming? — Quora
Contributing
Please kindly follow CONTRIBUTING.md to get started.
You can also contribute by sharing!
Share the list with your classmates, your friends and eve...
problems described in the book are really hard but they are explained in such
a way that even
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