those for which I determined that obtaining an accepted verdict is impossible.
, These problems continue to occupy the list of unsolved problems in the
PROBLEMSET, and there is no
→ Pay attention
→ Top rated
| # | User | Rating |
|---|---|---|
| 1 | Benq | 3676 |
| 2 | Kevin114514 | 3659 |
| 3 | jiangly | 3640 |
| 4 | turmax | 3450 |
| 5 | tourist | 3408 |
| 6 | strapple | 3360 |
| 7 | Um_nik | 3354 |
| 8 | squareOf105 | 3348 |
| 9 | maroonrk | 3312 |
| 10 | idontwannadothis…e | 3191 |
→ Top contributors
| # | User | Contrib. |
|---|---|---|
| 1 | Qingyu | 154 |
| 2 | nik_exists | 151 |
| 3 | maspy | 149 |
| 4 | AmShZ | 146 |
| 5 | Um_nik | 143 |
| 6 | Errichto | 139 |
| 7 | BledDest | 136 |
| 8 | adamant | 135 |
| 9 | maroonrk | 133 |
| 10 | cry | 130 |
→ Find user
→ Recent actions
You can use several words in query to find by all of them at the same time. In addition, if you are lucky search understands word forms and some synonyms. It supports search by title and author. Examples:
305— search for 305, most probably it will find blogs about the Round 305andrew stankevich contests— search for words "andrew", "stankevich" and "contests" at the same timeuser:mikemirzayanov title:testlib— search containing "testlib" in title by MikeMirzayanov"vk cup"— use quotes to find phrase as istitle:educational— search in title
Results
1.
0 Problems Remaining [日本語記事(For Japanese Speakers)](https://maspypy.com/codeforces-all-ac)
----
Previous post: https://codeforces.me/blog/entry/150057
Submission: [submission:384239819]
2026/07/26 03:13:42 JST (2026/07/25 18:13:42 UTC)
I have solved every problem in the Codeforces PROBLEMSET except for those for which I determined that obtaining an accepted verdict is impossible.
# Scope
I considered the problems listed in the [PROBLEMSET](https://codeforces.me/problemset).
I have solved very few problems from the [GYM](https://codeforces.me/gyms). The only collection I worked through systematically was the PROBLEMSET.
I determined that it is theoretically impossible to obtain an accepted verdict for the following 31 problems:
[problem:775A], ([92101](https://codeforces.me/problemset/problem/921/01) ... [92114](https://codeforces.me/problemset/problem/921/14)), [problem:927A], [prob...
2.
I've completed Project Euler It was a beautiful journey full of internet digging, searching for patterns, learning stuff, fighting with formulas on paper, making crazy observations, coming up with brilliant ideas, implementing crazy optimizations, waiting for the programs to finish, suffering when something was wrong, and so on (and each of the mentioned not once not twice took multiple hours).
It's been a couple of months since I was left with the last unsolved problem and finally I did it! I didn't give up and I obtained the answer alone, without anyone's help, like in the rest of the problems (I was using only internet sources created before the publication of the problem). I'm writing this blog because I am bursting with joy and I wanted to share it with the community. I highly recommend PE as most of the problems were definitely very high quality (and some were a real pain in the ass, but they still teach how to overcome stuff that you're uncomfortable with).
Here's a little souvenir for me:
3.
Valentine's Day Contest 2020 Hello everyone!
Will you be single and bored during Valentine's Day? Never fear, as [user:zscoder,2020-02-06] is here to cure your boredom.
I would like to invite you to Valentine's Day Contest 2020, which will take place on [Friday, February 14, 2020 at 12:30 GMT](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200214T2030&p1=122&ah=3&am=30). The contest is unofficial and unrated, but the quality of most (if not all) of the problems are comparable to problems from a Codeforces round. I am the author of all problems.
The contest format will be IOI format, which means that each problem is worth $100$ points, and there are subtasks for each problem. There will be no time penalty. The problems are **not sorted in increasing order of difficulty**. Unlike IOI, you are allowed to use any templates or notes you have.
There are **7 problems** to be solved in **3.5 hours**. There is an interactive problem, so feel free to learn about them [here](https://codeforces.me/...
Problem B: Unsolved during contest time :(
Announcement of Valentines Day Contest 2020
4.
WF23 Luxor _(Long blog ahead. Reader discretion advised.)_
I feel we have a rather interesting WF story (note: we did the 47th finals, as the University of Maryland, <b><i>as 2 people</i></b>... explained below), so I figured I'd tell it.
Exposition
----------
It actually starts way before WF, too. Our teams were decided on (some form of) merit based on an internal qualifier. My team for the regional and NAC (North America superregional) ended up as {me, [user:Navick,2024-04-24], [user:mr.banana,2024-04-24]}. We did [fairly](https://nasouth22d1.kattis.com/contests/nasouth22d1/standings) [well](https://nac.icpc.global/wp-content/uploads/2023/06/NAC23-scoreboard.pdf) in those. However, for WF, my two teammates only had single-entry visas for the US, meaning that if they left, they couldn't come back into our country. So they couldn't really go with me...
Luckily, in such situations, ICPC lets you just replace your teammates. So we held another internal qualifier, and ended up with two ...
E was unsolved entirely), and yet, it was still feasible for me to solve. It
was definitely lucky, gone for one of the other unsolved problems (B/E/J at the time). But I didn't
know that, so I didn't, to be solved (only before E and J, where J got two solves across both 46 and
47 and E wasunsolved
5.
Are we close to machines solving ICPC problems? Hi, all,
I with few other folks at [NEAR](http://near.ai/blog) work on teaching machines to program. A particularly exciting sub-project of that is teaching machines to solve competitive programming problems.
In this post I would like to give a quick overview of where the state of the art is today, what the major challenges are, why this is not a popular area of research, and how the CodeForces community can help to address some of the issues the program synthesis community is facing today.
We also have a certain budged allocated for this project, and we are paying to the CodeForces members who help us with some data annotation challenges. We have paid more than $10k in our first two annotation projects, and are launching three more projects today. Scroll to the end if you are interested.
Competitive programming as a benchmark
======================================
With the emergence of deep learning, neural networks started performing almost at a human level in many ta...
mostly unsolved as of today.
6.
Lockout Bot for codeforces Hello everyone, I'm sure many of you have been watching and enjoying the recent [lockout streams](https://www.youtube.com/watch?v=bBNIIg8REUU&feature=youtu.be) organized by [user:ecnerwala,2020-06-08] and [user:scott_wu,2020-06-08] and would be wanting to compete with your friends in a similar format. I have made a discord bot that does exactly the same. The source code for the bot can be found [here](https://github.com/pseudocoder10/Lockout-Bot).
The bot gives a set of 5 problems with ratings from [x, x+400], where x is chosen by you and the point distribution is [100, 500]. The first person to solve a problem gets the points for it. The match ends when someone has >= 800 points or 45 minutes have been elapsed. The bot automatically updates the status when someone solves a problem but you can also do it manually.
To invite the bot to your discord server, click [here](https://discord.com/oauth2/authorize?client_id=669978762120790045&permissions=0&scope=bot). If you don't wanna ...
type `.match accept` and the bot will chose 5 random unsolved problems by both
the participants in, To accept a challenge, simply type `.match accept` and the bot will chose 5
randomunsolved
7.
[Tutorial] On Range LIS Queries, Part 1 Hello, Codeforces!
At some point of life you want to make a new data structure problem with short statement and genius solution. LIS (Longest Increasing Subsequence) is a classic problem with beautiful solution, so you come up with the following problem:
* Given a sequence $A$ of length $N$ and Q queries $1 \le i \le j \le N$, compute the length of Longest Increasing Subsequence of $A[i], A[i + 1], \ldots, A[j]$.
But on the other hand this looks impossible to solve, and you just give up the idea.
I always thought that the above problem is unsolved (and might be impossible), but very recently I learned that such queries are **solvable** in only $O(N \log^2 N + Q \log N)$ time, not involving any sqrts! The [original paper](https://arxiv.org/abs/0707.3619) describes this technique as *semi-local string comparison*. The paper is incredibly long and uses tons of scary math terminology, but I think I found a relatively easier way to describe this technique, which I will show in t...
up the idea. I always thought that the above problem is unsolved (and might be
impossible), but, I always thought that the above problem is unsolved (and might be impossible),
but very recently I
8.
fix problem ratings pls (the rainboy effect) [The first few paragraphs of this blog, above the first spoiler, are just for story purposes and are irrelevant to the problem statement]
One fateful day, a naive and young version of me from about 5 days ago had a dream. A dream to stop being so terrified of hard problems. A dream to conquer the most challenging stuff that CF ever had to offer. A dream to... ok, enough of that, that's so stupid. Basically, I've been grinding 3500s lately, mostly for fun (and my god, has it been fun).
Two days prior, I found myself solving [1919G](https://codeforces.me/contest/1919/problem/G). That went fine, but after getting it, I noticed that despite G being 3500, it wasn't even the hardest problem in the contest — that honor went to the next problem, [1919H](https://codeforces.me/contest/1919/problem/H) (the subject of this blog), which had **no solves in-contest**. I concluded that I would have to be insane to try that, and moved on to other problems.
Well, yesterday, I decided I...
alternate example, the two contest-unsolved problems from [Pinely
2](https://codeforces.me/contest/1863, submissions shortly after the contest/system testing ended), but most other
contest-unsolved problems do, -unsolved problems from [Pinely 2](https://codeforces.me/contest/1863) have
their appropriate 3500
9.
Bayan 2015: Finals [Final scoreboard](http://contest.bayan.ir/en/contest/final_2014/scoreboard/)
[Introduction](/blog/entry/17541)
[Arrival](/blog/entry/17631)
[History](/blog/entry/17633)
[Some photos from contest and closing ceremony](/blog/entry/17733)
Interview with Bayan CEO Ali Ghadiri and some photos from the event will be published tomorrow
Places 10-15 received bronze medals
Top 3 receive gold medals. Silver medals for next several places: 4. Adrian Budau 5. Peyman Jabbarzade 6. Pooya Zafar. Places 7-9 also received silver medals, unfortunately I could not keep up with announcers
Nikola Djokic is third!
Ali Haghani is second. Congratulations!
And the winner is Evgenii Kapun aka ~eatmore,2015-05-02
Winners will be announced shortly!
Speeches, videos and performances — all the usual things for closing ceremony.
Closing ceremony is underway. We'll know winners shortly
Scoreboard is frozen
|Place|Name|Country |A |B |C|D |E|F|G |H |Score|
|-...
solved as well. Only problems D and F are unsolved (though I solved them both
during test run) 1, 1:53 Problem G is solved as well. Only problems D and F are unsolved (though I
solved them both
10.
SWERC 2022-2023 <img src="/predownloaded/70/37/703737cf76db63e4b7bbb9fd63a01a3dc446371e.png" style="width:250px; float:right; margin: 0 1em 1em 1em"/>
The Southwestern Europe Regional Contest will take place on the 19th of February in Milan.
It is the ICPC regional contest (i.e., the winning teams will advance to the ICPC World Finals) for teams from France, Israel, Italy, Portugal, Spain, and Switzerland.
The mirror contest [contest:1776] will be held on Codeforces at [contest_time:1776] and will last 5 hours.
The mirror contest will contain the problems from the official competition plus some additional problems.
I am the chief judge for the competition and I want to thank:
- The amazing set of judges who proposed and prepared the problems: [user:cescmentation_folch,2023-01-24], [user:cip999,2023-01-24] (vice chief judge), [user:gangsterveggies,2023-01-24], [user:giove,2023-01-24], [user:gog.gerard,2023-01-24], [user:jinlifu1999,2023-01-24],
[user:Petr,2023-01-24], [user:Simon,2023...
solution. So, morally, this problem is still unsolved! In the next days I
might decrease the time, , morally, this problem is still unsolved! In the next days I might decrease
the time limit. We have a
11.
Codeforces Raif Round 1 Editorial [problem:1428A]
------------------
Setter: [user:bensonlzl,2020-10-17]
Prepared by: [user:errorgorn,2020-10-17]
<spoiler summary="Hint 1">
Consider when $x_1=x_2$
</spoiler>
<spoiler summary="Hint 2">
Consider when $x_1 \ne x_2$
</spoiler>
<spoiler summary="Solution">
We consider 2 cases.
The first is that the starting and ending point lie on an axis-aligned line. In this case, we simply pull the box in 1 direction, and the time needed is the distance between the 2 points as we need 1 second to decrease the distance by 1.
The second is that they do not lie on any axis-aligned line. Wabbit can pull the box horizontally (left or right depends on the relative values of $x_1$ and $x_2$) for $|x_1-x_2|$ seconds, take 2 seconds to move either above or below the box, then take another $|y_1-y_2|$ seconds to move the box to $(x_2,y_2)$.
</spoiler>
<spoiler summary="Code (C++)">
```c++
#include <bits/stdc++.h>
using namespace std;
int main(){
ios_base::...
**Bonus $2$ (unsolved):** Solve for $0 \leq a_j \leq 4$.
Tutorial of Codeforces Raif Round 1 (Div. 1 + Div. 2)
12.
SecondThread vs. galen_colin Lockout Duel (ft. neal, stevenkplus) SecondThread vs. galen_colin Lockout Duel (ft. neal, stevenkplus)
==================
Good morning everyone!
There are three great unsolved questions on Codeforces that every pupil dreams to one day know the answer to:
- What's the best opening move when playing the Epsilon Guessing Game against a geometry problem?
- How many cyans is [user:Um_nik,2020-11-27] worth, modulo $10^9+7$?
- Who is *really* the 229th best programmer on Codeforces: [user:SecondThread,2020-11-27] or [user:galen_colin,2020-11-27]?
While we may never know the answer to the first two, Colin and I will settle the third question once and for all this Sunday in a 1v1 duel! Don't miss it!
Join us at [this time on Sunday](https://www.timeanddate.com/worldclock/fixedtime.html?msg=SecondThread+vs.+galen_colin+Lockout&iso=20201129T0830&p1=234&ah=1) where we will compete head-to-head in a 1v1 lockout at https://www.twitch.tv/nealwu, with live commen...
morning everyone! There are three great unsolved questions on Codeforces that
every pupil dreams to, There are three great unsolved questions on Codeforces that every pupil dreams
to one day know the
13.
Personalized competitive programming ladders Hello Codeforces!
For the past couple of years I have been developing a competitive programming platform that would aggregate solutions from different OJs. It was initially written for assigning tasks for my preparations (and some professors used it in our university for grading students in algorithmic courses).
Recently I have been developing a "ladders" feature, because I wanted to train and realized that this would be the best way to do it. Now, I am excited to say that I have decided to "go public" with this feature and invite you to try it out.
### How it works
Do the steps below:
- Create an account at https://competitive.herokuapp.com
- Add your handles to your profile (Codeforces/Atcoder/etc.)
- Go to ladders and start solving problems
- When you start a task, a 2-hour timer starts; you have to solve the task in this time limit
- Tasks that are solved successfully are marked green, tasks that were unsolved are marked red
- You can also see a leaderboard with...
marked green, tasks that were unsolved are marked red - You can also see a
leaderboard with the, successfully are marked green, tasks that were unsolved are marked red - You
can also see a leaderboard
14.
Codeforces Data Scraping Websites There are many useful websites that extract data from Codeforces and give some statistics, problem recommendations, graphs, etc.
I thought that collecting them all in one place would be a good idea. Please comment the websites you find useful :D
List as of now:
- [CF-Predictor](https://cf-predictor-frontend.herokuapp.com/) ([Original Blog](https://codeforces.me/blog/entry/50411)): Predicts the expected rating change during and after contests.
- [Code-Drills](https://code-drills.com/) ([Original Blog](https://codeforces.me/blog/entry/48991)): Recommends problems for a list of user & gives statistics on total number of problems solved.
- [Codeforces Visualizer](https://cfviz.netlify.com/) ([Original Blog](https://codeforces.me/blog/entry/50326)): Gives various statistics for a user, and supports comparison between two users.
- [CF Statistics](https://cfstatistics.herokuapp.com/) ([Original Blog](https://codeforces.me/blog/entry/60775)): Comparison between 2 users ...
"unsolved problems" as opposed to Codeforces' last 15 unsolved., and which haven't been solved (but attempted). Essentially, a complete list of
"unsolved problems" as
15.
Indian ICPC Camp 2026 ## Greetings Codeforces!
This year, that pride comes with something new: some of India's strongest competitive programming communities are stepping up to help the next generation make the same leap. IIT Roorkee, IIT BHU, IIT Delhi, IIIT Hyderabad, IIT Indore, IIT Kanpur, IIIT Delhi, IIT Hyderabad, IIT Madras, IIT Kharagpur and IIIT Bangalore will each be hosting one week of this year's camp — several of them home to teams heading to the World Finals themselves. Each host college will also conduct a class on a topic relevant to their week's contest, so you're not just solving problems set by these communities, you're learning directly from them. The people setting your problems and running your contests this year are drawn from the very communities pushing India towards the top of competitive programming. If that isn't motivation to give this camp everything you've got, we don't know what is.
With that, we're...
have solved. There have been multiple instances of easier problems going
unsolved due to leaderboard, that other teams have solved. There have been multiple instances of easier
problems goingunsolved due
16.
Checklist for OI Problems (WebApp) Hello Everyone,
I guess everyone who is preparing for OI already know about this [Checklist for OI Problems](https://codeforces.me/blog/entry/59422) prepared by [user:ko_osaga,2018-11-01]. I've been using this for quite a long time, and it is really helpful!
But since the checklist gets updated from time to time, I found it hard to migrate from the previous checklist to new checklist. So, I made the following web app for the same purpose! Now you don't need to worry about migrating, I can just add the problems to database and it'll update automatically!
Link: [OI Checklist](https://oichecklist.pythonanywhere.com)
Please find the features and changes to the main checklist bellow:
Features and Changes
------------------
1. First of all, now the checklist contains direct link to each problem, while the main checklist had link to some parent of the link. And clicking on a contest name will lead to the official "Task" page of that contest, which generally contains jud...
state of a problem is easy, just click on the cell. It will change state from
unsolved to solving to, 5. Toggling state of a problem is easy, just click on the cell. It will change
state fromunsolved
17.
[ICPC blog series #0] My last ACM experience Disclaimer
==================
This isn't really a first tutorial in the series. If you are interested in reading what participating in ICPC World Finals feels like, you can enjoy my <s>pathetic</s> behind-the-scenes story of the Cambridge silver-medal performance in WF2020. I tried to write a spoiler--free blog so that it contains minimum information about the problems.
Motivation
==================
In 2016 I have written a blogpost [My first ACM experience](https://codeforces.me/blog/entry/48082). It made sense to me to also close some chapter of the book by writing up about how my last serious contest went. I advise not to take the blog too seriously, it is just an honest stream of consciousness (some facts may not even be 100% accurate, though I will fix things people point me). Feel free to comment, praise, <s>or hate</s>. For a different perspective, check out [user:IBaloff,2021-10-07]'s [blog](https://codeforces.cc/blog/entry/95526).
The hero and heroine of the story o...
solved by any team at that time. H, K, L, N remained unsolved and in some
cases even unattempted. David
18.
Indian ICPC Camp 2025 Greetings Codeforces!
---------------------
Indian ICPC Camp 2025, proudly sponsored by Go For Gold (powered by NST), is organized jointly by leading Indian institutes including IITs, NITs, IIITs and BITs. This camp is a continuation of last year’s massively successful edition, which saw participation from over 3000 teams across India.
## Schedule
Contest window: 31 August 2025 – 19 October 2025
Contests every Sunday, 2 PM – 7 PM IST (unless otherwise mentioned via Discord/WhatsApp).
First contest: 31 August 2025.
Ranklist freeze after 4 hours.
## Educational Sessions
Alongside contests, we’ll host topic-focused sessions by some of India’s best competitive programmers — including ICPC World Finalists and Codeforces Grandmasters. These will cover advanced algorithms, data structures, and problem-solving strategi...
instances of easier problems going unsolved due to leaderboard-bias. So attempt
unsolved problems too, multiple instances of easier problems going unsolved due to leaderboard-bias.
So attemptunsolved problems
19.
Introducing cp-notes.com — a place for your interesting competitive programming problems! **Update in 2025:** I've mostly forgotten about this site, but recently something rather funny came up: I was looking for a way to get a relatively large number of free subdomains (name of the url not mattering at all), when I realized I was still paying for cp-notes.com. So I tried to login to the AWS account owning the domain (which I haven't done in years), but it prompted me to check the email associated with it for a verification code... Unfortunately, I had used my Columbia university email out of convenience, but that has been disabled! (which I suspect has something to do with me dropping out?) I actually can still update the website (not that I was planning to) since I have some keypair saved which allows programmatic access, but not being able to use the console is a huge pain. I could also contact AWS support, but I feel like that would take a while...
Anyways, it is time for me to express some of my frustrations: Fuck Columbia University! In addition to disabling my emai...
solved/unsolved problems from several different competitive programming
platforms. You can write
20.
I wrote a contest every day in 2025 and finally reached IGM! Hi Codeforces!
I was a ICPC contestant 10 years ago. In the past few years, I sometimes came here to participate some contests, and wandered between Candidate Master and Master.
One year ago, I wanted to reach IGM in 2025. I decided to write a contest every day.
I try to solve all the problems below 2400, and keep the unsolved 2400~2900 problems in my mind.
I keep thinking these problems, only look for editorial when I really can't figure it out.
Fortunately, I got a great performance in the last Div.1 and reached IGM.
Thank you to all the contest authors, I enjoyed every contest and every problem.
I will take a 6-month break and keep the IGM title.
Then I will start over again and try moving towards LGM, see you soon in June.
Wishing everyone get great performance in new year!
the unsolved 2400~2900 problems in my mind. I keep thinking these problems,
only look for editorial, I try to solve all the problems below 2400, and keep the unsolved 2400~2900
problems in my mind. I
21.
CP trainer — a new tool for training Hello, <br/>
I created a project for training and analyzing your performance during contests: [cp-trainer.com](https://cp-trainer.com). I believe it has some unique features non-existent in competitive platforms and can provide as a more sensible tool for training, especially for more experienced users, who have participated already in a bunch of contests. Below I will briefly discuss its functionalities:
Problem recommender
------------------
In this section, we will discuss the heuristics used for problem recommender, the system offers for the user 10 problems with the highest value of this heuristics. First we need to introduce a couple of metrics:
<ul>
<li> <b> get_dict_accuracy </b> — Dictionary of form (<b>tag</b> : average number of submissions to accept problem with this tag during contest) </li>
<li> <b> ratings_average_time_diffs </b> — Dictionary of form (<b>rating</b> : average time in seconds to solve the problem with this rating during contest) </li>
<li...
* Average rating of solved/unsolved problems — This shows, what is the
average highest
22.
CodeForces Statistics Tool Beta 1.0 Hi my second family,
After long thinking I decide to share my statistics website with you & because of currently I have no time I will stop developing it but soon I will back again.
**UPD Latest Contest**
_Codeforces Round #322 (Div. 2)_
[Play with it](http://smartcoder.me/cf)
Let's Go
--------
**-CodeForces Contestants Populations**
Do you want to see where Grandmasters live take a look at Contestant population page
if you are not a Grandmaster don't worry you can see your rating also ,you can swap between ratings with click and unclick
**-CodeForces standing filtered by country**
Standing filtered by country and barchart about solved & unsolved problems during contest.
it support teams
*
✅
- **Make upvotes and downvotes changable.**
✅
- **Add unrated registeration.**
✅
## UI/UX Improvements
- **Make official dark mode.**
- **Make the folder icon in the catalog clickable so that we can collapse certain columns while searching.**
- **In Fav. Blog Entries Option, blogs should be collapsed by default so that we can see multiple favorite blogs at one time otherwise it takes a lot of scrolling to see...
24.
World Finals: Live 15:24 — Closing ceremony will start shortly and you can watch it on ICPC Live. That's probably it for this translation. Bye-bye, see you soon
[cut]
15:10 — Moscow SU finished with 6
14:55 — I'll try to ask all top teams about number of problems they had solved right after the contest
14:51 — Tokyo trying to solve 2 almost simultaneously. Were they success?
14:48 — Seems like Gennady submitted B and very nervously walking in backgrounnd while Niyaz working on B. An by the wave of joy it seems they got it
14:28 — SPb SU get I quite likely. They are now seem to work on B
14:18 — Seems like SJTU got E right. Meanwhile ~tourist,2013-07-03 is seems to type B currently
14:08 — Based on their reaction Warsaw seems to have got something accepted. I probably would rather focus on video feeds of top teams, sorry for not fulfilling all photo requests
14:05 — Perm State University:
, for example.
**Important Information**:
- Rank List (Scoreboard): https://codedrills.io/contests/icpc-amritapuri-2020-regional-round/scoreboard
- Contest Page: https://codedrills.io/contests/icpc-amritapuri-2020-regional-round
- Contest Blog: https://codeforces.me/blog/entry/93818
- There are **726** qualified teams who will be competing for the world finals slots from this regional!
- Contest Duration: **4 hours**.
- Tentative Start Time: **18:30 IST**
**Announcements**:
- All problems have a memory limit of **1GB**, and solutions that exceed this would be marked as RTE instead of MLE due...
6, and puts the number of distinct problems solved at 8. 3 problems still
remainunsolved. We will, ! 4 problems still remain unsolved. ([Ranklist](https://i.gyazo.com, unsolved.
([Ranklist](https://i.gyazo.com/3c07f418142a8252eadcc7bd9625ec7e.png)) - **21:30
26.
Everything about Codeforces scoring system This is a tutorial to how Codeforces scoring system works and some basic strategies about it. I will only explain about rated rounds here, but note that there are other types of scoring in unrated contests.
Please do share this blog when you see questions about it.
Scoring types
------------------
There are two different types of scoring system:
- Standard (Div. 1 / Div. 2, Div. 1 + Div. 2)
- Extended ICPC (Educational, Div. 3, Div. 4)
The standard (this is not a formal name, but I don't know if one exists) scoring is Codeforces' own scoring system where each participant's rank is determined solely by their **final score**. On the other hand, extended ICPC literally uses the ICPC rule for calculating ranks, using **number of solved problems & penalty**, with slight modifications.
Standard
------------------
Contests using this scoring system have pre-determined initial scores on each problem. By initial it means you get that score when you solve it in the $0$-th min...
**solved** problem. Unsolved problem has NO penalty no matter how many
attempts you made on that, either the problem becomes unsolved with no other 'Accepted' submission, or
that submission becomes, . Unsolved problem has NO penalty no matter how many attempts you made on that
problem. Let's say the time
27.
UserScript to toggle on/off problem tags from the problem page itself. Problem tags could spoil a problem, so chances are you like to keep the problem tags switched off.
Even so, you would probably like to know about the problem difficulty (or rating) or sometimes have a quick look at the tags and retry a problem before moving on to the editorial.
It could be very tedious to go to your profile and change the settings to enable the tags, then after you finish your work, switch it off again.
This extension can solve both of the issues for you.
<br>When tags are hidden
<br>After you click on the button
Download Instructions :-
1. Download an user script manager like [Tamper Monkey](https://www.tampermonkey.net/).
2. Download the script from my [Github Repo](https://github.com/vishalagrawal22/tag-hider-codeforces).
3. **Switch off** "show tags for unsolved problems".
<spoiler summary="What is the extension doing behind the scenes">
**Problem:** Sim...
3. **Switch off** "show tags for unsolved problems"., unsolved problems". **Problem
28.
Codeforces Upsolving Helper <spoiler summary="UPD(July 24, 2020)">**Randomize Button** added at the end of each section in **All Problemset Recommender** .
</spoiler>
<spoiler summary="UPD(July 19, 2020)">
**Unattempted Problem Recommender** from **Past Contests** (as suggested by [user:sharatsachin,2020-07-20] and [user:mr_robot11,2020-07-20]) and from **All Problemset** (as suggested by [user:ekaerovets,2020-07-23]) has been introduced .
</spoiler>
<spoiler summary="UPD(July 14, 2020)">
**Team Mode** has been introduced as suggested by [user:socho,2020-07-13].
</spoiler>
<spoiler summary="UPD(July 11, 2020)">
Rated and Unrated Problems are now separated under respective headings in each section(when Problems are segregated by Index) as suggested by [user:gol_en_05,2020-07-12] .
![ ](https://drive.google.com/uc?export=view&id=1Z6aO...
all your Unsolved problems of Codeforces that you attempted (submitted their
solution at least, 1. Compiles at one place all your Unsolved problems of Codeforces that you
attempted (submitted, 1. Currently, on the Codeforces website, we could not see all our **unsolved
problems** at once
29.
A WhatsApp Bot for Codeforces Analytics, Visualizations, and More Hello Codeforces community,
------------------
I wanted to share a useful WhatsApp-based AI assistant that might help with our competitive programming workflows. The idea is to bring essential tools directly into your chat, saving the time you'd spend switching between different websites.
One of the most interesting features is its ability to generate a "true performance" graph for any user, which visualizes your performance rating in every contest.
How to Use
------------------
Click the link to open a chat: [Whatsapp Chat Link](https://puch.ai/mcp/ycGISc7uVo)
Send the pre-filled message that appears.
The bot will then be active and you can start sending commands.
Available Tools
------------------
Here is a list of its few functionalities. You can ask for them in natural language (e.g., "plot my rating graph" or "recommend a problem for me").
###Analytics & Information
`get_codeforces_user_stats`: Fetches detailed stats for one or more users.
`recommend_problems`:...
`: Recommends unsolved problems based on rating. `get_solved_problems`: Shows a
list of most, `recommend_problems`: Recommends unsolved problems based on rating.
30.
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...
First, you need to know that Hash Killer III is currently an unsolved Open
Problem. So, time
31.
Some Cool Hacks of Dark Reader Hey Everyone!
First of all, **"Merry Christmas"** and **"Happy New Year"** to all, hope you all would be doing good :)
#### Hack #1: Fix Background for Dark Reader
As codeforces's looks gets changed between christmas and new year's eves so due to change in background some of us who use dark reader or any dark themes would be facing issues while exploring codeforces.
<spoiler summary="like this :(">
</spoiler>
So if you facing the same issue you may do following to get the following result :)
<spoiler summary="like this :)">
</spoiler>
You just need to add the following code to dev tool of "Dark Reader" for "codeforces.com" under "CSS".
~~~~~
body{
background:url(..) !important;
}
~~~~~
#### Hack #2: Remove/Hide Tags for Codeforces Problems
As you would have to download any additional extension to hide ...
the tags for unsolved problems via codeforces settings(but once a problem get
solved tags get visible!)., the tags. Or you may be disabling the tags for unsolved problems via
codeforces settings(but once a
32.
Rating the Difficulty of Codeforces Problems **Update:** Due to popular request, we created a script for you to generate your own rating profile. For detailed instructions, refer to our [ui page on github](https://github.com/yjiao/codeforces-api/tree/master/ui). We plan to rewrite our code in Javascript to expand functionality, but hopefully this is helpful in the meantime. Please let us know if you have any suggestions!
This project was written jointly with [user:yj12,2016-07-28].
Several heuristics exist for finding suitable practice problems on Codeforces. One common piece of advice is to sort all problems by the number of solvers and to work down the list. However, the number of solvers depends on a number of factors, including the recency of the contest, and the date and time the contest was held. Another heuristic is to try to solve problems at a certain level, for instance, all Div. 1 C problems. However, the difficulty of such problems can vary greatly from contest to contest.
We decided to create a better measur...
is especially apparently in a few problems that are unsolved by Div. 2
participants but have been, problems that are unsolved by Div. 2 participants but have been solved by Div.
1 participants. This
33.
Insomnia 2016 Brace yourselves, Insomnia is coming!
PAG and SDSLabs, IIT Roorkee bring to you their flagship programming contest, Insomnia'16.
Contest begins 21:00 IST on 9th of April, 2016
It will be a team event (upto 3 members). Languages allowed are C/C++ and Java. The contest will consist of 20 problems, tough enough to keep you engaged for the entire duration.
It is being conducted on our own platform, [CodeVillage](https://codevillage.sdslabs.co/).
Carrying forward the tradition of Insomnia, which started as an overnight programming contest, it is the second consecutive time that it is being organised as an 24-hour contest.
Problem setters include members of 11coders, ACM-ICPC world finalist for this year and previous world finalists as well.
Follow the event at our facebook [event page](https://www.facebook.com/events/195338937517187/).
**Update:**
Cash prizes worth 40K INR to be won!
Overall: 1st Prize — Rs. 15,000 2nd Prize — Rs. 10,000
Indian Teams: 1st Pr...
after solving 5 problems. 8 problems are still unsolved. Register now and
solve them!, sequentially, now faces the hardest problem of the set, yet unsolved. It's
going to be interesting to see how, . 8 problems are still unsolved. Register now and solve them! **Update 3:**
With just a, 4 problems still unsolved! Register at https://codevillage.sdslabs.co/ to see
if you can solve
34.
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...
exercises are left unsolved, as they are intended to be worked through by the
reader.
35.
IOI graders: linking C with Pascal and Java Good time of the day.
As some of you know, ~yeputons,2014-08-19 and I have an archive of IOI-tasks. While preparing it, we had understood, that we have no resources to prepare graders for all languages,so we want to find a way to write a grader only for C, and to link other languages to it.. Also, I think it's better to have one grader and adapters to avoid code duplicating, which can cause errors.
There were some problems with linking Pascal, but they were mostly solved. I'll write about one unsolved problem further. It would be very good if someone have ideas how to solve it.
Next year Java will be available on IOI. So I tried to write Java adapter for graders.
[Here](https://yadi.sk/d/aYWQG5Uva3K6w) is one for the problem 2010.cluedo.
I think this one works well.
I publish this because I think someone else can be interested in it. Also I have some problems, which I don't know how to solve. Probably someone here can solve them.
First of all, we need to include `jni....
one unsolved problem further. It would be very good if someone have ideas how
to solve it. Next, unsolved problem further. It would be very good if someone have ideas how to
solve it.
36.
Invitation to Insomnia 2024 Hello, Codeforces!
The Computer Club of MNNIT Allahabad, India, is thrilled to invite you to its annual programming contest— **Insomnia**! An ACM-ICPC style team programming competition held on Codeforces, as part of our tech fest, **Avishkar**.
What Awaits You?
- Intense 3 Hours of Coding
- Teams of Up to 3 members
### **Prize pool : INR 15,000**
**Winner: INR 10,000**
**Runner up: INR 5,000**
Mark your calendars, gather your team, and get ready to compete on [contest_time:565733]
[Contest Link](https://codeforces.me/contestInvitation/ad6c644c98973f15f1a18c39a8889d1ec58d6190)
==================
Registration link for MNNIT students: [Link](https://forms.gle/W1Qx5EFfbMFfYTKT6)
Problem Setters: [user:Aditya.Rai,2024-11-14], [user:lucifer223,2024-11-14]
Problem Testers: [user:Aditya.Rai,2024-11-14], [user:lucifer223,2024-11-14], [user:amansingh27,2024-11-14], [user:current_newbie...
**: [user:SmolBrain,2024-11-20] and [user:shiven,2024-11-20] Problem H —
Remainedunsolved, Problem H — Remained unsolved
37.
Chrome/Firefox Extension to analyse Codeforces profiles ### Hello coders!!
Recently I have developed a chrome extension which analyses codeforces profiles and presents the chart/data on the profile webpage itself. Just open any profile on Codeforces after installing this extension.
[**Install Now for Google Chrome**](https://chrome.google.com/webstore/detail/hhljbjodjdbjbggddjaidojnlmaobcpo)
[**Install Now for Mozilla Firefox**](https://addons.mozilla.org/en-US/firefox/addon/cf-analytics/)
Also, you can find the source code on [Github](https://github.com/ApoorvaRajBhadani/cf-analytics).
The chart includes —
1. Problem rating chart — Bar chart for the number of problems solved for each problem rating
2. Tags chart — Doughnut chart for the number of problems solved for each tag across all problems
3. Unsolved problems — Gives the count and also lists all unsolved problems.
Extension in action:
The UI blends easily wi...
problems 3. Unsolved problems — Gives the count and also lists all unsolved
problems., . Unsolved problems — Gives the count and also lists all unsolved problems.
Extension in action
38.
Daily Diary (Competitive Coding in Summers) I realised that there is only one way improve one's skill, and that is through practice. So I decided to practice more topics and more problems on codeforces and different judges. This is simply a daily record for what I did through my vacation.
I also want to tell you about **stopstalk.com** . It is a good site to make and keep you daily coding record.
##**16 MAY 2017**
##### **Problems Solved** -
###### 1. http://codeforces.me/problemset/problem/535/D
This was a simple problem and it used Z function for prefix length calculation
###### **solution link** — http://codeforces.me/contest/535/submission/27152004
###### 2. http://codeforces.me/problemset/problem/551/B
Although the problem was simple, I had some trouble in understanding the language of the problem. It took time more than required.
###### **solution link** — http://codeforces.me/contest/551/submission/27160921
<br>
##### **Participated Contest** -
I participated in a v...
##### Problems Unsolved -, ##### Problems unsolved -, ###### It would be a great help if someone could help me with the unsolved
problems.
39.
LeekCF Rating 2.2.0 is out **Faster, blurred tags, rank colors, and settings!**
Get it here: [Chrome Web Store](https://chromewebstore.google.com/detail/leekcf-rating/fnkoldggbbjmndapidpegfpkkokboklp) | [Firefox Add-ons](https://addons.mozilla.org/en-US/firefox/addon/leekcf-rating)
Hi everyone! A new version of LeekCF Rating, the extension that shows a problem's rating without spoiling its tags, is now available. Here's what changed.
**Tags are revealed one at a time.** Tags now appear blurred. If you're stuck, click a single tag to get one hint instead of seeing all of them at once. "Show All Tags" still works if you want everything.
<img src="/predownloaded/17/ed/17ed535a4e02d9f921393ad389a13c191e43e0ab.png" width= 350px> <img src="/predownloaded/18/34/183465b775353548d9cd23edbaf814937058d433.png" width= 350px>
**New display features.** The rating is now colored by Codeforces rank, from gray to red, and you can see how many people solved the problem. For fully blind practice, you can also hide ...
Codeforces tags turned on.** You no longer need to turn off "Show tags for
unsolved problems." If, to turn off "Show tags for unsolved problems." If Codeforces' own tags box is
showing, the extension
40.
Invitation to CodeRed 2026 
# Hello Codeforces!
Ready for a high-intensity ICPC-style battle?
We are excited to announce **CodeRed**, one of the flagship competitive programming events of **Aparoksha**, the annual tech fest of the **Indian Institute of Information Technology Allahabad**.
If team strategy, whiteboard arguments, last-minute hacks, and the sweet sound of *Accepted* excite you, this contest is for you.
---
## Contest Details
**Date:** 12 April 2026
**Time:** 5:00 PM – 8:00 PM (IST)
##### **Contest Link**
Kindly use the invitation link below to register for the contest: https://codeforces.me/contestInvitation/baac2882fdbed30238dedbb68160772bfcde6bff
##### **Finals (Offline Round)**
Top performing teams from the **online round** will be invited to the **offline finals at IIIT Allahabad**.
The finals will be conducted **on campus**, where selected teams will compete in an intense **ICPC-style s...
Note: In case any question remains unsolved, the prize money allocated for that
question will be
41.
My first ACM experience Hey!
Polish Collegiate Team Programming Contest (AMPPZ 2016) took place today, organized by University of Wroclaw. This is my first ACM experience, and I want to share with you my impressions.
To begin with, I'm still a high schooler (2nd grade). However, thanks to generosity of UWroclaw organizers team and some charity institutions, a few best high school teams were able to participate.
Now let's talk about the contest. My teammates were Paweł Burzyński([user:pawelek1,2016-10-29]) and Kacper Kluk ([user:wonrzrzeczny,2016-10-29]). None of us is a really fast coder, so we just decided to focus more on accuracy than speed. As we'll see later, this was kind of a good idea.
The contest started with no delays. I was not expected to be the coding monkey, but somehow it happened that three first and easiest tasks were accepted by me. These were not really challenging, so let's just ignore this fact. Some time later, Kacper scored the "ifologic" problem C. Then, the difficulty ha...
an interesting F and Kacper was implementing G. B was still unsolved, but we
were giving it a try, , Paweł scored an interesting F and Kacper was implementing G. B was still
unsolved, but we were giving
42.
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...
back to contests that you participated in way earlier, and solving harder
unsolved problems one good
43.
HackerEarth Collegiate Cup Final Round Results Hi Everyone,
We conducted the final round of the HackerEarth Collegiate Cup on 5th November, 2016. There were 2 contests. One was the [Onsite Round](http://hackerearth.com/hackerearth-collegiate-cup-onsite-round/) and other was the [Mirror Round](http://hackerearth.com/hackerearth-collegiate-cup-mirror-round/). There were 12 problems to be solved in 5 hours (ACM ICPC style) in both the rounds.
**Onsite Round:**
4 problems remained unsolved. Top 3 teams in the Onsite Round are:
1. FacelessMen ([user:alecsyde,2016-11-06], [user:TerryMcGinnis,2016-11-06], [user:Sahilgrover,2016-11-06]) : Indian Institute of Technology, Kanpur
2. FruitSalad ([user:yashkumar18,2016-11-06], [user:kuldeeppatel,2016-11-06], [user:Sumeet.Varma,2016-11-06]) : Dhirubai Ambani Institute for Information and Communication Technology
3. mobius_treap ([user:vmrajas,2016-11-06], [user:tanujkhattar,2016-1...
) **Onsite Round:** 4 problems remained unsolved. Top 3 teams in the Onsite
Round are: 1, 1 problem remained unsolved. Top 3 teams in the Mirror Round are:, 4 problems remained unsolved. Top 3 teams in the Onsite Round are:
44.
Where to Practice Topic wise for Competitive Programming ? **UPD** — We are sorry for the inconvenience faced by all. Now Website is Live again. Keep Coding ON.
Hello Codeforces!
_I hope all is well!_
**" Which website to practice? "** is always a confusing question for us. I felt the same when i started Competitive Programming.
Not to Worry now , i have created a website named [**Codedigger**](http://codedigger.tech/) which will solve this problem and boost your confidence in **Competitive Programming**.
#### How?
- We have collected handpicked problems from top 4 coding platforms — **_Codeforces, Codechef, UVa and SPOJ_** , All at One Place.
- A diversified List of **Topics** and before starting any topic you can also learn some amazing techniques on that topic through **video editorials** beforehand.
- You can test your knowledge by a **virtual contest** based on a particular topic and a video editorials will also be provided so you won't get stuck and further learn new concepts.
- You can also Practice To...
see all your unsolved questions at one place. Also You can sort it by Rating.
You can Improve your, **UPD2 :** Now you can see all your unsolved questions at one place. Also You
can sort it by Rating
45.
New Extension for AtCoder Hey everyone at Codeforces!!
Codeforces is a really well structured website, it is really easy to navigate to a problem and track your peers.
Atcoder on the other hand, though it does has some cool features feel hollow when compared to Codeforces. It is like being surrounded by walls.
So I have implemented a few features which are already present on Codeforces in AtCoder. I used Kenkoooo API to fetch rating for each problem and did get some inspiration from CF Analytics. Here are the features and the link to extension of course!!
**Link for the extension:** [AC Analytics](https://chromewebstore.google.com/detail/ac-analytics/fbliobpicoanacbncphlgaghdkodkgme)
Key Features
1. Activity Calander : Is added to better track your progress like in Github and Codeforces.
2. Problems Solved by Rating : See what you had been solving and up solve when needed.
3. Unsolved Problems : Easily identify and tackle unsolved problems to improve your skills.
4. Submission Histo...
. Problems Solved by Rating : See what you had been solving and up solve when
needed. 3.Unsolved, 3. Unsolved Problems : Easily identify and tackle unsolved problems to improve
your skills.
46.
My solutions didn't get evaluated on main tests Hello!
Yesterday I participated in Codeforces LATOKEN Round 1 (Div. 1 + Div. 2) and passed pretests on problems A, B, C, D, E during the contest. However, my solutions were not further evaluated on the main tests and they are still being displayed with "Pretests passed" in the submissions tab and as unsolved in the standings. This resulted in a delta of -302 :(.
I have never seen this before and I don't know what could have caused it. Does anybody know what went wrong or is it a bug? I'll also ping [user:MikeMirzayanov,2021-06-14], asking for help.
Sorry for writing an unuseful post but I don't know where else I should ask.
unsolved in the standings. This resulted in a delta of -302 :(.
47.
India ICPC — Amritapuri 2020 Regionals Results Hi ICPC Amritapuri Contestants,
It was originally planned to release the ranklist at the ceremony on 21st August, Saturday. However we got some feedback from the contestants that it will be important to know the ranks before other regionals. After discussions between the setting team and the RCD, we have decided to <b>provisionally release the ranklist subject to plag checks</b>. The solution discussion and award ceremony will still be on 21st August. Congratulations to the winners and hope you enjoyed the contest.
1. IIT- Roorkee — [user:amnesiac_dusk,2021-08-15] [user:piyushsethia1999,2021-08-15] [user:harshhx17,2021-08-15]
2. IIT Kanpur- [user:Dragnoid99,2021-08-15] [user:mohanraghug,2021-08-15] [user:abhinavvv306,2021-08-15]
3. DA-IICT- [user:nishant403,2021-08-15] [user:Jaydeep999997,2021-08-15] [user:harshrajani460,2021-08-15]
4. IIIT Hyderabad — [user:gaurav172,2021-08-15] [user:shaanknight,2021-08-15] [user:vivace_jr,2021-08-15]
5. Bits Pilani — [user...
Remained unsolved in the contest.Cubical had 1 AC and Lag had 3 AC.Top team
solved 8 problems,4 teams, Cat and Dice problem Remained unsolved in the contest.Cubical had 1 AC and Lag
had 3 AC.Top team
48.
[Website] CF UpsolveX — Automated Upsolving Companion for Codeforces (Web App + Chrome Extension) Hello everyone!
I built **CF UpsolveX**, an automated upsolving companion for Codeforces.
It consists of a full-stack web application along with a Chrome extension that helps you track, prioritize, and consistently upsolve the problems you missed in contests.
---
### Problem:
While participating in Codeforces contests, I often found myself saying:
*"I'll upsolve the remaining problems tomorrow."*
But after a few contests, dozens of unsolved problems start piling up and it becomes difficult to decide:
* Which problems should be upsolved first?
* Which contests still have pending problems?
* How much progress has been made overall?
* Whether I am actually being consistent with upsolving?
Since upsolving is one of the most important aspects of improvement in competitive programming, I felt there should be a better system for tracking and prioritizing missed problems.
---
### Solution:
So I built **CF UpsolveX**.
It automatically tracks your missed...
problems tomorrow."* But after a few contests, dozens of unsolved problems
start piling up and it, * **Contest History:** Solved vs Upsolved vs Unsolved statistics & Progress
tracking for every, But after a few contests, dozens of unsolved problems start piling up and it
becomes difficult to, Instead of showing hundreds of unsolved problems in a flat list, CF UpsolveX
ranks every problem
49.
OI Duel Bot Hi, I made a duel bot where you can challenge other users in a OI styled duel. It is sort of like a combination of regular duel matches and lockout challenges. You can find the bot at [OIDuelBot](http://t.me/OIDuelBot). The bot is currently available only for Telegram, but I have plans to make one for discord as well.
### Rules
You can challenge other users in a OI styled duel. In the duel, you have to race against time to solve the subtasks before your opponent. If your opponent solves a particular subtask before you, they gets the point for that subtask, and you won't get any points for it even if you solve it in the future. The player with more points at the end of the duel wins the challenge.
### How to use
First, you need to add the bot in a telegram group. Here are the commands you can use in the bot
`/register [oj.uz username]` — you have to register yourself in order to enter your duel
`/challenge [telegram username]` — you can challenge other user...
. ### How the bot works When you challenge a user, you will get a random problem
unsolved by, When you challenge a user, you will get a random problem unsolved by both users
from [oj.uz](oj.uz
50.
Сайт "Unsolved Codeforces Problems" — Лучше его аналогов? <spoiler summary="Предисловие">
На самом деле я должен был опубликовать этот пост год назад, однако из-за некоторых проблем мне не удалось опубликовать его, а дальше и вовсе забыл об этом всём. Лучше поздно чем никогда :)
</spoiler>
<spoiler summary="Разве нет на данный момент подобных сайтов? -_-">
_Я знаю, что это не единственный сайт, который показывает список нерешенных задач пользователя Codeforces, но я бы не стал делать его, если бы не имел преимуществ перед другими :)_
</spoiler>
**Всех приветствую.** Я создал open-source сайт, показывающий список нерешенных задач в Codeforces с использованием (*барабанная дробь*) API Codeforces.
<spoiler summary="Больше скриншотиков">
</spoiler>
#### Сайт доступен по данной [ссылке!](https://azer.is-a.dev/unsolved-cf-problems/)
Исходный код проекта доступен на [GitHub](https://github.com/sadykhzadeh/unsol...
"Unsolved Codeforces Problems" website — Better than others?, Сайт "Unsolved Codeforces Problems" — Лучше его аналогов?, created a site that shows a list of unsolved Codeforces problems, but I
wouldn't do this site without, not the first person who created a site that shows a list of unsolved
Codeforces problems, but I, ### Why is "Unsolved Codeforces Problems" better than its analogues?, ### Чем же "Unsolved Codeforces Problems" лучше своих аналогов?, #### Website is avaiable [here!](https://azer.is-a.dev/unsolved-cf-problems/), #### Сайт доступен по данной [ссылке!](https://azer.is-a.dev/unsolved
-cf-problems/), **Hi, everybody.** I created an open-source site that shows a list of unsolved
CodeForces problems, /unsolved-cf-problems/) Исходный код проекта доступен на
[GitHub](https://github.com/sadykhzadeh, You can find source code in my [GitHub](https://github.com/sadykhzadeh/unsolved
-cf-problems), Исходный код проекта доступен на [GitHub](https://github.com/sadykhzadeh/
unsolved-cf-problems)
51.
What If... Virtual Contests were REAL? [cfscripts] Hey everyone!
With inspiration from
* the great [research](https://codeforces.me/blog/entry/86596) by [user:galen_colin,2022-06-25].
* [user:MiuraMiuMiu,2022-06-25]'s [Codeforces Anytime](https://codeforces.me/blog/entry/83122).
* ... and of course the various Codeforces performance predictors!
I proudly present **cfscripts**. *cfscripts* is a collection of scripts for Codeforces that uses the [cf-API](https://codeforces.me/apiHelp) to do different things.
For instance, *cfscripts* includes a script named **What If?** (yes, very fancy), which allows you to **simulate Codeforces contest rating changes** over time, but **including virtual and unofficial contests**.
You can choose to include only positive rating changes (this feature is dedicated to [user:galen_colin,2022-06-25]).<br/>
You may ask: *...
rating at the time of participating). * **Unsolved Contest Problems** - Find
unsolved problems, your rating (the rating at the time of participating). * **Unsolved Contest
Problems** - Find
52.
Introducing Lynkforces -- A Smarter Way to Practice Ever felt like Codeforces tags are too limited? [Lynkforces](https://lynkforces.vercel.app/) (pronounced link-forces) lets you fly around a 3D map of problems and discover clusters by reasoning and technique. Click points to fly to problems, see related ones, adjust rating, and enter your handle to see solves!
Full link: [lynkforces.vercel.app](https://lynkforces.vercel.app/)
## What it is
- Two maps:
- Reasoning — clusters by similarity of how you think about the solution.
- Tags — clusters by techniques/data structures (segment tree, DSU, XOR basis, etc.).
- Color key: white = unsolved & not relevant (default), green = solved, purple = relevant (darker = more relevant), blue = solved + relevant (darker = more relevant).
- Dataset note: coverage isn’t comprehensive; latest I saw while testing was about a year back (Round ~995-ish). 3D clustering isn’t perfect since high-dimensional vectors were compressed to 3D, so some related points may still be far apart.
Main map...
= unsolved & not relevant (default), green = solved, purple = relevant (darker
= more relevant), blue, .). - Color key: white = unsolved & not relevant (default), green = solved,
purple = relevant (darker = more
53.
Meet IT Codeforces Round Editorial Thank you very much for taking part in the contest!
<spoiler summary="Contest timeline">
- -0:05. Starting the chat with the Questions Answering team: [user:tnowak,2020-11-15] and our beloved coordinator [user:antontrygubO_o,2020-11-15]. We hope that there won't be that many questions :)
- -0:01. One minute to go! I hope that everything goes smoothly. I'm so afraid of posting the editorial accidentally that I moved this timeline into another blog...
- 0:01. First blood in Div2! Congratulations to [user:majorro,2020-11-15]!.
- 0:03. First blood in Div1 as well! Congratulations to [user:Errichto,2020-11-15], your knapsack is ready for a journey to win!
- 0:04. [user:Sho10,2020-11-15] first to solve Div2B. Well done!
- 0:05. We also have the first question. So far so good...
- 0:06. [user:Um_nik,2020-11-15] gets the first pretests pass in Div1B. The cheaters are caught!
- 0:09. [user:bandiaoz,2020-11-15] packs the first Knapsack in Div2! A difficulty spike is coming...
- 0:12....
successful attempt on Div1F. There's still one more unsolved task left... -
1:13. [user:ksun48,2020-11-15
Tutorial of Codeforces Round 683 (Div. 1, by Meet IT)
Tutorial of Codeforces Round 683 (Div. 2, by Meet IT)
54.
CodeChef strike chrome extension Hello coders,
probably some of you know [CodeChef](http://www.codechef.com/) (another programming contest page).
Why am I writing about another page? Because I believe, that when you want to make your rating higher, you have to compete in contests. Some coders think, that practice and contest are the same (just solving the problems), but definitely they are not for me. In contest I'm under the pressure (time pressure, fear, that if I do not solve the problem my rating will be lower, ...) and so I'm doing a lot of mistakes in real contest (like not reading statement carefully, missing some conditions, trying to submit quickly without precise testing and so on).
[cut]
That's why I want to share with you, that on CodeChef page there are long contests. For me it's something in the middle between practice (no competition, no fun) and competition, because you are not under the time pressure.
But real reason, why I'm writing about CodeChef long contests is, that I worte extensi...
for unsolved problems , last result for unsolved problems
55.
Only Div 2 round = BIG PROBLEM Hello CF community!
This blog is my way to draw attention and perhaps start an initiative to solve one big problem on Codeforces.
Before every only div 2 round,CF get hundreds of 'new ingenious users' , and they done all problems, have around 5-6 hacks per round and become candidate masters.That means no opportunity for regular div 2 competitors to jump with rating and feel how to be a winner.Maybe this is unsolved problem , but if we try together to stop this , I belive that we will achieve ceratin results.
Now I will write some of my suggestions , I'd love to read your :)
First:
Div 1 competitions are rarely ,but everybody who prepare tasks for only div 2 contest can ask someone with a high rating to help him around the idea of the most difficult problems.This is certainly reduce only div 2 contest.I think that the best users like [user:tourist,2015-03-01] ,[user:Petr,2015-03-01],[user:WJMZBMR,2015-03-01]... give some advice and help about preparing(Maybe I a...
div 2 competitors to jump with rating and feel how to be a winner.Maybe this is
unsolved problem, winner.Maybe this is unsolved problem , but if we try together to stop this ,
I belive that we
56.
Regarding authorship of problems Suppose than person A comes up with an interesting task, but is not able to solve it. Then, A sends this problem to his friend B and asks for help in solving it. After B successfully does that, the question appears: whose problem is that, A's or B's?
I don't like the approach when A is considered an author as in that case he can, for example, just spam B with tons of statements he just came up with without any intuition if those are solvable, and that doesn't sound as highly intellectual work. From the other hand, I don't like approach when B is considered the author too: he is doing the same amount of job as any contestant would do during the contest. A more interesting example: if A sends his problem to both B and C and they solve it with a difference of 5 minutes. Would be weird to say they both are coauthors, would be weird to say that the first one who solved is author either.
To avoid confusion, I just prefer not to share my unsolved problems with anyone, but in this case, ...
To avoid confusion, I just prefer not to share my unsolved problems with
anyone, but in this case
57.
Codechef Snackdown 2017 Qualification Round and my feelings after solving all !!! It is one of the most happiest and excited moment in my coding life !!
Solved all the problems of Codechef SnackDown 2017 Contest (Qualification Round) !!
Now our team rank is 1 (combined).
I am unable to express my excitement and how much fun I have got by solving the last problem !!
Today I had an mid term exam. But till yesterday, we solved 2 problems out of 4, still there was two unsolved problems.
Azad Abul Kalam sir told us to solve the rest. Sakib vai also inspired me.
Then I try to solve the third one. In my first attempt I solved that problem.
Since I had a mid term exam today, I thought to skip the last one. So I just read that problem and came out from the contest.
But from the time of reading the last problem, only this thinking was running in my head, "How to solve this?". I just couldn't give attention to anything else. Whatever I was trying to do, just this thinking was making me mad. I couldn't do a single math for today's exam. In the mean time ...
two unsolved problems. Azad Abul Kalam sir told us to solve the rest. Sakib
vai also inspired me., unsolved problems. Azad Abul Kalam sir told us to solve the rest. Sakib vai
also inspired me
58.
CodeHunt: A Site for Problem Filtering and User Comparison Hi Coders! We have launched **[CodeHunt](https://codehunt.cc)**!
**[CodeHunt](https://codehunt.cc)** is made to help **Codeforces** and **UVa Online Judge** users filter their problems with convenience and ease. You can also compare yourself with friends and rivals to motivate your practice and growth.
What inspired us to make CodeHunt?
----------------------------------
Before any other site, we practiced our competitive programming using **UVa**, assisted, of course, by the incredible site, [uHunt](https://uhunt.onlinejudge.org/), made by _Felix Halim_. As we began to participate in **Codeforces** contests and solved more and more problems here, we never had the same level of motivation for the long grind as we did when using **uHunt**. We realized it was because there wasn’t a tool out there for **Codeforces** that was as convenient in tracking problems.
After a while of looking for the right tool...
**filtering** of problems (Difficulty, Solved, Unsolved, Attempted, Included
Tags, Excluded Tags, and more, problems (Difficulty, Solved, Unsolved, Attempted, Included Tags, Excluded
Tags, and more) - Multiple
59.
ICPC Gwalior-Pune 2020 Regionals Results Hi ICPC Gwalior-Pune Contestants, We are provisionally releasing the ranklist subject to plag checks. Congratulations to all the winners and hope you enjoyed the contest.
1. IIT- Bombay; [user:TheOneYouWant,2021-08-15] [user:BhaskarTM,2021-08-15] [user:Shivam_18,2021-08-15]
2. IIT Guwahati- [user:Enem,2021-08-15] [user:zeus_iitg,2021-08-15] [user:BrownieTK,2021-08-15]
3. IIT Madras- [user:Kira_1234,2021-08-15] [user:KDVinit,2021-08-15] [user:rtzrtz,2021-08-15]
4. IIT Kanpur; [user:aryanc403,2021-08-15] [user:umang99m,2021-08-15] [user:_Aaryan_,2021-08-15]
5. IIT Kharagpur ; [user:cheems,2021-08-15] [user:bhagwa_brigade,2021-08-15] [user:RahulSenpai,2021-08-15]
Pass-the-message,House Hunting and La La Langton's Ant problems Remained unsolved in the contest.Shinobu had 1 AC and Wakka and Molly had 2 AC.Top team solved 7 problems.
The full scoreboard is available at https://codedrills.io/contests/icpc-gwalior-pune-2020-regional-round/scoreboard
The goal is simple:
> Given my public submission history, what should I practice next?
The system uses Codeforces as the strongest source because it provides public submissions, verdicts, problem ratings, tags, rating history, and problemset metadata. It also has adapters for LeetCode and CodeChef, but Codeforces is the main difficulty anchor.
---
## 1. Main idea
AlgoRadar converts public CP activity into explainable features and ranks unsolved problems by **learning value**, not just rating or popularity.
Rough pipeline:
```
handle
-> fetch public submissions/problem metadata
-> build profile/tag/difficulty features
-> classify focus areas
-> estimate solve probability
-> rank candidate problems
-> buc...
AlgoRadar converts public CP activity into explainable features and ranks
unsolved problems by
61.
CF Analytics Pro, because the numbers don't lie, they just don't talk. Hi Codeforces,
Like many of you, I spend a lot of time on Codeforces but I have always felt the profile page tells you *what* you solved, not *how* you solve.
After a few months of looking at my own submissions manually (rating distribution, weak tags, unsolved problems), I decided to automate the parts I kept checking by hand. I also added two small quality-of-life features along the way: one-click bookmarks on any problem, and auto-fill on the submit page.
The result is **CF Analytics Pro** a small browser extension that adds analytics to any Codeforces profile.
[cut]
<br>
#### What kept bothering me
Four small frustrations pushed me to build this:
- Codeforces shows a flat "problem count" per tag, but not where the unsolved ones actually are.
- There is no easy way to see "what should I practice next?" you have to filter the problemset manually.
- Bookmarking is buried in the "Add to favourites" flow.
- You finish a problem, click submit, and then realize you...
(clickable). A **Weak Topics** section surfaces tags where you have unsolved
problems and links to a, my own submissions manually (rating distribution, weak tags, unsolved
problems), I decided to, **Unsolved tab**: Problems you have attempted but never solved, grouped by
persistence Stuck (5, , unsolved problems), I decided to automate the parts I kept checking by hand.
I also added two small, - Codeforces shows a flat "problem count" per tag, but not where the unsolved
ones actually are
62.
Codeforces Mobile Companion App Hi everyone!
I’ve always found myself checking my Codeforces profile, and contest history quite often – so I thought, why not make a mobile app for it? (PWA)
**Features-**
**View Your Rating & Contest History:**
Check your current rating, max rating, rank, and all past contests with ease.
**Rating vs Problems Solved Graph:**
A unique graph showing how many problems you've solved at each rating level!
**Track Submissions & Solved Problems:**
Browse your full submission history, filter by verdict, and view detailed submission stats.
**...
just a tap! **Full Problemset Browser:** Filter problems by tags, difficulty,
solved/unsolved, **Full Problemset Browser:** Filter problems by tags, difficulty, solved/
unsolved/unattempted
63.
Hi guys check out my new website cf-cool-graphs (WITH COOL GRAPHS) I know there's already hundreds of cf analytic projects but trust me i have cool graphs to show. check out the website on
https://cf-cool-graphs.vercel.app/
Cool Features:
Performance Calculator:
-> Calculate your in-contest and virtual performance (i know tle bot can calculate performance but it doesn't do virtual performance); virtual performance is just an estimate based on your placement compared to the official rankings;
Because I am poor the calculations will take a bit of time so sorry about that; but we do cache the calculations so it is faster next time; I also cache the contests queried if it is not yet cached so it will be faster the more the service is used;
Rolling Average:
-> Gives your 50-problem rolling average ratings; This is my favorite graph to be honest; its a good tell if you are improving or not, even if the rating is quite flat; I attached my recent 50-day average an...
problem after contest; The upsolve rate is strictly based on the next unsolved
problem of the contest but, the next unsolved problem of the contest but the upsolve count also counts
problems after that; Say
64.
Why editorials are so hard to understand ? Hi,
as usual, when you ask someone in codeforces tips on how to improve with the most amazing feature of this site has (that's constant contests rounds), they are all equal: compete, read all problem statements and then read the editorial to solve the unsolved ones. I follow this step by step, but when I reach the last one I fail completely.
What I mean is, why is so hard to understand most (Most because from the top of my head I can recall really good editorial writers like [user:zscoder,2017-06-05] and [user:Errichto,2017-06-05]) of editorials here ? Sometimes is like the contest writers want us to get inside their brain and understand what they mean by some paragraph. I get it, is really difficult to be great in explaining things, maybe the hardest thing in the job of creating a contest.
But sometimes I think it only requires time and effort. Some of the most interesting contest & editorials I've seen had depictions of how the idea of the algorithm works, or lots and lots ...
problem statements and then read the editorial to solve the unsolved ones. I
follow this step by step, statements and then read the editorial to solve the unsolved ones. I follow
this step by step, but when
65.
Codeforces Visulaizer Hello cool coders! This is my first post on CF. This is to share a small tool I built using the codeforces api.
Give it a try here: [http://cfviz.netlify.com](http://cfviz.netlify.com/). The source is available [here](https://github.com/sjsakib/cfviz). Please let me know if you found any bug or issue.
Current features are:
Single User Analytics
---------------------
- Verdicts chart
- Languages chart
- Tags chart
- Levels chart
- Total tried problems count
- Total solved problems count
- Average and max attempts
- Count of problems solved with one submission
- Max AC for a single problem (It indicates in how many ways someone solved a problem)
- List of unsolved problems
Comparison between two users
----------------------------
- Current, max and min rating
- Number of contests
- Best and worst position in contest
- Max positive and negative rating change
- Compared rating time-line
- Total tried problem count compared
- Tot...
of unsolved problems, single problem (It indicates in how many ways someone solved a problem) - List
ofunsolved
66.
How do you track unsolved and revision problems? This is what I tried I’m still quite new to competitive programming. I practice problems on multiple platforms, and I often struggle to keep track of what I’ve solved, what I’ve skipped, and what I need to revise later.
During contests and regular practice, I usually end up with a few good problems that I want to revisit. However, after the contest, those problems often get buried in browser bookmarks or are forgotten completely, which makes revision difficult.
I also tried maintaining an Excel sheet, something that Vivek Gupta ([user:acraider,2025-12-17]) suggested in one of his videos. While the idea itself makes sense, I found it hard to keep updating it regularly. Manually copying links, switching tabs, and filling in details after every problem felt time-consuming, and over time I simply stopped maintaining it consistently.
To reduce this friction, I ended up building a small Chrome extension .The main idea was to make problem tracking feel effortless, so I wouldn’t skip it after practice.
...
How do you track unsolved and revision problems? This is what I tried, - Optional bookmarking for unsolved Problems., unsolved problems to revisit later. It’s still a simple and evolving tool, but
it directly addresses
67.
Introducing Daily CF— Your Smart Problem Recommender for Codeforces Hey everyone!
=============
I’m excited to share something I’ve been working on — a Chrome extension called Daily CF.
It’s built to make your Codeforces practice more focused, consistent, and effortless by recommending daily personalized problems right inside the Codeforces interface.
### What is Daily CF?
Daily CF is a minimal, integrated extension that adds a new section named “→ CF Daily” to your Codeforces sidebar.
Every day, it suggests a small set of problems tailored to your current rating and problem history — so you can start solving instantly without wasting time deciding what to do next.
### Key Features
**Daily Personalized Problem Set**
Each day, Daily CF selects a fresh batch of unsolved problems near your current rating range using the Codeforces API.
You can also refresh manually anytime with the “Find”...
**Daily Personalized Problem Set** Each day, Daily CF selects a fresh batch of
unsolved problems
68.
After the Square869120Contest #4(Atcoder) In Apr/09/2017, there was a contest in Atcoder.<br />
The contest name is "Square869120Contest #4". [Click here](https://s8pc-4.contest.atcoder.jp/)<br />
<br />
How was it?<br />
Please write and discuss here about impressions and "qustions about solutions".<br />
<br />
Thank you for everyone.<br />
It is also advisable to solve those who are not participating or unsolved problems as past problems.<br />
<br />
=========================================================================================================<br />
past Square869120Contest<br />
Square869120Contest #4:[Click here](https://s8pc-4.contest.atcoder.jp/)<br />
Square869120Contest #3:[Click here](https://s8pc-3.contest.atcoder.jp/)<br />
Square869120Contest #2:[Click here](https://s8pc-2.contest.atcoder.jp/)<br />
Square869120Contest #1:[Click here](https://s8pc-1.contest.atcoder.jp/)<br />
<b>Update: If you can, please answer [the questionnaire](https://goo.gl/forms/m3DteS1XE54Z8TTN2) for the improv...
everyone.
It is also advisable to solve those who are not participating or unsolved
problems as, unsolved problems as past problems.
69.
CPOS: a local terminal + VS Code workflow for Codeforces/CSES practice Title: CPOS: a local terminal + VS Code workflow for Codeforces/CSES practice
Content:
Hi everyone,
I built **CPOS**, a local-first tool for competitive programming.
The main idea is to have one place for the parts of CP practice that usually get scattered across browser tabs, notes, extensions, and memory.
Tools like **CPH** are already very good for the editor-side workflow: capture a problem, create a file, run samples, submit, etc. CPOS is partly inspired by that workflow, but the goal is a bit broader.
CPOS has a terminal UI where you can manage practice, contests, submissions, and progress from one place.
[cut]
From the TUI, you can:
* browse Codeforces and CSES problems
* connect your Codeforces and CSES accounts locally
* open problems
* run samples
* submit solutions
* view upcoming and live contests
* track rating changes
* see an activity heatmap
* analyze weak tags
* get 30 recommended unsolved problems around your level
The TUI is the...
changes * see an activity heatmap * analyze weak tags * get 30 recommended
unsolved problems around, heatmap * analyze weak tags * get 30 recommended unsolved problems around your
level The TUI is
70.
CP-Vertex — 1v1 Duels and Weakness-Oriented Training Hi everyone!
Over the past few months I've been building **CP-Vertex**, a training platform designed around one simple idea:
> Most tools can tell you **what your weaknesses are**. Very few tell you **what to practice next.**
The goal of CP-Vertex is to bridge that gap.
Website:
https://cpvertex.vercel.app/
Source Code:
https://github.com/aristoncodes/CP-Vertex
---
## The Training Loop
Instead of randomly picking problems, CP-Vertex follows a simple workflow:
> **Analyze your profile → Identify weak topics → Practice them → Test yourself in a duel → Upsolve missed problems → Repeat**
The focus is on helping you improve the topics that actually limit your progress.
---
## 1v1 Duels
Challenge another programmer to a live duel.
Problems are automatically selected around both players' ratings, making matches competitive rather than one-sided.
Features:
* Automatic problem selection
* Live progress updates
* Spectator mode
* Server-side d...
. * **Upsolve Tracker** — Automatically queues unsolved contest problems so
they don't get forgotten
71.
30 day challenge Hello everyone !
I'm fourth year software engineering student.I've been doing CP for three years .I learned many algorithms and I solved many problems but the problem is that I cannot do my best during contests for that I'm going to set myself a 30 day challenge :making virtual participation every day in a contest and upsolve all unsolved problems.
so if any one remember a good round (quality of problems,gap of difficulty between problems)please share it with me.
I'll update the blog every day to post my rating in the contest and let's see if this challenge gonna make me a
junior tourist ^__^.
first contest:[round 422](https://codeforces.me/contest/822)
[rank](https://codeforces.me/contest/822/standings/participant/31810110#p31810110):1368
second contest: [round 480](https://codeforces.me/contest/980) [rank](https://codeforces.me/contest/980/standings/participant/31837825#p31837825):1058
third contest: [round 353](https://codeforces.me/contest/675) rank:[1398...
every day in a contest and upsolve all unsolved problems. so if any one
remember a good round
72.
CodeForces Daily POTD (Problem of the Day) Tamper Monkey Script Hi,
I wrote a simple Tampermonkey script that adds a **POTD (Problem of the Day)** button on Codeforces.
Clicking it will give you a problem with a rating similar to your current rating.
**Links:**
- [Download Script (GreasyFork)](https://greasyfork.org/en/scripts/560655-cf-potd)
- [GitHub Repo](https://github.com/saitamapunches123/CF-POTD)
---
### DESIGN CHOICES
1. **Minimize API Calls During Contests**
All API calls are done **only when clicking "POTD"**, making the button slightly slower to respond, but keeping page refresh fast and lag-free during contests.
2. **User-Specific POTD**
Each user gets a **different POTD**, depending on their current rating (`curr_rating`).
3. **Rating Range**
POTD will be in the range: `[curr_rating - neg_delta*100, curr_rating + pos_delta*100]`
- `curr_rating` is rounded down.
- Example: If a user's rating is **1650**, POTD can be one of **[1400, 1500, 1600, 1700, 1800]**.
- You can cha...
change the distribution by modifying the `neg_delta` and `pos_delta`
constants. 4. **Unsolved, 4. **Unsolved Problems Only** POTD will **always be an unsolved problem**,
unlike LeetCode, unsolved problem**. This makes the POTD button work as both a **Problem of the
Day** and a **random
73.
CF Explorer : Your utimate Codeforces companion Hello, Codeforces community!
==================
First of all, I would like to thank [user:MikeMirzayanov,2025-04-04] for such an awesome platform. It’s been almost 2.5 years since I joined this community. From my experience, I believe analysis is key to improving problem-solving skills. Many beginners don’t analyze their weaknesses, solve problems randomly, or struggle to stay consistent. As a beginner, I made these mistakes too! That’s why I was motivated to develop a tool to make the Codeforces experience more enjoyable and effective.
**Introducing [CF Explorer : Your utimate Codeforces companion](http://cfexplorer.vercel.app)**.
How CF Explorer may help you:
#### Never Miss a Contest
- Upcoming contests in a beautiful slider view with a **countdown timer**.
- One-click **calendar reminders** to schedule contests instantly!
<spoiler summary="Screenshots: Homepage">
</spoiler>
#### Analysis on ...
types of **analysis on users submission**. - Find your weak points: A list of
attempted-but-unsolved, your weak points: A list of attempted-but-unsolved problems. - Rating history
& contest performance
74.
Codeforces during COVID-19 Hey guys!
I hope you and all your families are well and safe during this outbreak. May the sick be healed and the well stay well.
It is apparent that many of us now have significantly more free time on our hands, at least temporarily, and this is evidenced by the spike in participation to an astonishing 20,000 yesterday. Personally, I am spending more and more time on this website solving problems, and I'm sure many of you are too!
This is why I think it would be an excellent idea if we ramp up activities on this website, and create more fun community things to keep us busy with. (I'm not talking about only more contests, we can be creative in our activities).
I'm a relative newcomer to the site, so I don't know how exactly this could happen, but I certainly have some ideas:
1) The most obvious thing would be to increase the frequency of rated contests immediately, to accommodate for the spike in demand (as of now there are more people registered for the div 3 in two day...
(Reds, I'm looking at you) an unsolved CS algorithm? I would love to hear your
ideas; you guys, target, by a large number of skilled people (Reds, I'm looking at you) an
unsolved CS algorithm?
75.
Insomnia 2015 Qualifier (Team programming contest) Hi,
I want to invite you to the annual programming competition of MNNIT Allahabad, India, which is an ACM-ICPC style team programming contest of 3 hours duration.
**Prizes**
Members of top 2 teams will win Codechef goodies.
**Contest details**
Contest timings: Check [here](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Insomnia+2015+Qualifier-+MNNIT+Allahabad%2C+India&iso=20150906T2130&p1=2408&ah=3)
Contest link: https://www.codechef.com/INSQ2015
**Problem setters:**
[INSQ15_A](https://www.codechef.com/problems/INSQ15_A/) : [user:codefor6768,2015-09-07], [INSQ15_B](https://www.codechef.com/problems/INSQ15_B/): [user:kunal_rocks,2015-09-07], [INSQ15_C](https://www.codechef.com/problems/INSQ15_C/): [user:nishant_141077,2015-09-07], [INSQ15_D](https://www.codechef.com/problems/INSQ15_D/): [user:mgajabi,2015-09-07], [INSQ15_E](https://www.codechef.com/problems/INSQ15_E/): [user:amanmittal,2015-09-07], [INSQ15_F](https://www.codechef.com/problems/INSQ15_F...
:) **Second place:** [user:yancouto,2015-09-07] Still one problem left unsolved
, lets see who gives it a, Still one problem left unsolved, lets see who gives it a green tick first :P
76.
Upsolve it — Stop Guessing What to Solve on Codeforces ### Hi Everyone
<div style="overflow: hidden;">
<img src="/predownloaded/ea/3c/ea3ca5038d21aed7d64db88b0596f90924dd225f.png"
style="float: right; width: 400px; margin-left: 25px; margin-bottom: 15px;" />
<p>
If you train regularly on Codeforces, you've probably faced this.
</p>
<p>
You open a gym<br>
You see a long list of problems<br>
You spend time deciding what to solve
</p>
<p>
Is this too easy? Too hard? Even useful?
</p>
<p>
Most people don't struggle with solving.<br>
They struggle with <b>choosing what to solve</b>.
</p>
</div>
---
#### The Idea
I built **[Upsolve it](https://upsolve-it.hnuicpc.tech)**, a tool that gives you a structured way to train based on your level.
* No random picking
* No guessing
* No wasted time before solving
---
#### What It Does
* **Level-based training:** reads your Codeforces rating and hands you problems at the right difficulty, hidden until the session ends. You can also adjust the level ma...
targeting a different skill * **Automatic upsolving:** every unsolved problem
lands in a queue so, unsolved problem lands in a queue so you actually come back and finish it *
**Interactive learning
77.
CSES Pro: Collapsible Progress Dashboard, Codeforces-style Copy/Paste & Star Bookmarks Hello Codeforces Community!
The CSES Problemset (cses.fi) is widely considered one of the best platforms for mastering core algorithms and data structures. However, compared to platforms like Codeforces, it lacks a few quality-of-life features that can make your practice workflow much smoother.
Specifically:
1. You have to save your code to a file locally just to upload and submit it.
2. There are no copy buttons on the input/output sample test cases.
3. There is no built-in way to bookmark/star tasks you want to review later.
4. There is no dynamic category-wise progress tracker, solve streak counter, or random problem selector.
To solve these annoyances, I built CSES Pro -- a lightweight, completely free, and open-source Chrome Extension that injects these features directly into the native CSES site.
---
## Feature Showcase
### 1. Codeforces-Style Submit Editor
No more saving temporary .cpp or .py files on your desktop just to upload them. The extension repl...
* **Interactive SVG Donut Chart** showing solved vs. unsolved ratios. * **Daily
Solve Streaks
78.
Don't open that blog post ### What does the project do?
It takes input from the user:
- Rating Boundaries (min, max)
- Some tags (Optional, if no tags selected, all tags will be included)
- Number of problems (N)
- Some codeforces handles (Optional, can be added one by one or comma separated)
- All the above preferences can be saved/erased locally, so you can close your browser and come in any time and find your preferences ready for you
The app gives (N) codeforces rated problems (problems with not rating/tags are not included) their ratings are between min and max (inclusive), all of them do not have any tags out of the tags selected above:
if the user selected `number theory`, `math`, and `dp`, then all these combinations are valid and can be seen in the outputted problems:
- `number theory`
- `math`
- `dp`
- `dp`, `math`
- `dp`, `number theory`
- `math`, `number theory`
- `math`, `number theory`, `dp`
but you will not see none of these:
- `binary search`, `m...
and the (N) problems the user will have must be unsolved with any of the
handles entered.
79.
AI for Good - AI Blitz#3 Competetive Machine Learning )
Hello Codeforces!
**AIcrowd and AI for GOOD** are driven to solve real world problems through challenges and collective effort of the data science community.From experts to enthusiasts we appreciate and value the participation and contribution of each and every single member of the community.
We realised, that at the heart of solving these varied, complex , open-ended and sometimes 'yet-unsolved' real world challenges, lies the crucial art of problem solving, an art which is very much what this brilliant community of CodeForces is all about!
So we welcome you all to participate in our [AI for Good — AI Blitz #3,](https://www.aicrowd.com/challenges/ai-for-good-ai-blitz-3?utm_source=post&utm_medium=post&utm_campaign=codeforces) a **21 day competition** for all AI/Ml enthusiast,with prize pool of **1000 CHF** with a touch of competitive programming especially for you guys. The following are the puzzl...
heart of solving these varied, complex , open-ended and sometimes 'yet-unsolved
' real world, -unsolved' real world challenges, lies the crucial art of problem solving, an
art which is very much
80.
Responsible AI: Why Governance And Sustainability Matter Just As Much As Algorithms We spend hours finding elegant solutions to nicely stated problems. In competitive programming, problems come tied with restrictions, inputs, and outputs. But when you're dealing with artificial intelligence, the “problem statement” isn’t even written yet — and that is riskier than any unsolved Div. 1 problem on Codeforces.
The Unspoken Aspect of Progress in AI
The majority of the talk depicts AI as absolute progress: faster, better, smarter. But the real world is messier. Large models require massive power, sometimes equivalent to the annual electricity of countries. Around the same time, the same models are sold as climate optimizers and solutions. This “AI paradox” — technology both problem and solution — forces us to ask the question: do we really build responsibly?
Bias is another iceberg beneath the surface. If training data reflects social inequalities, models will replicate them. Generative systems already spread misinformation at scale, threatening trust in journalism...
intelligence, the “problem statement” isn’t even written yet — and that is
riskier than anyunsolved Div
81.
CodeForces Helper — App to bring more Competitive Programming to mobile devices ! To all Codeforces lovers out there,
[user:vraj1408,2020-11-17] and I have developed an app which will help you guys to do CP on mobile devices easily.
We have used API's provided by codeforces.
App is having following features currently,
1. View User's profile with statistics
2. Checkout all upcoming contests
3. Upsolve the problems from contests in which user took part
4. View problem statement, search any particular problem by name, sort problems rating wise
5. Bookmark problem to solve in future or **download the problem statement to solve it offline**
6. View User's last 50 submissions
7. User's unsolved problems
8. View statistics of any user
and many more...
you can checkout our app on google play store by visiting provided link
[App on Google play store](https://play.google.com/store/apps/details?id=com.codeForces.Helper)
(App's name is **CodeForces Helper**)
Big thanks to [user:devaar100,2020-11-17] for providing us a platform where we ca...
7. User's unsolved problems
82.
Introducing CFinsights: Your One-Stop Solution to All Things Codeforces CFInsights — Your One-Stop Solution to All Things Codeforces
======
So you’re grinding CF contests and solving problems every day, but… how do you actually track your progress?
How do you know what’s working, what’s not, and what to fix? That’s why I made **CFInsights** — your full performance dashboard and comparison tool for Codeforces.
Try it here: https://cfinsights.netlify.app/
This blog will tell you:
- **What is CFInsights**
- **What are its two powerful modes**
- **Why I made it (and maybe you feel the same)**
- **How to reach out and suggest stuff**
Let’s go
What is CFInsights?
----
**CFInsights** is a web app that helps you deeply analyze your Codeforces performance and track your improvement.
It uses the official Codeforces API and gives you clean, easy-to-read dashboards — whether you're just starting out or already a specialist.
**You don’t need to sign up. Just enter your handle and get a full breakdown of your CP journey.**
The Two...
- Difficulty breakdown (Very Easy to Very Hard) - Last 10 unsolved problems -
**CFInsights Rating
83.
How to unsubmit a previously submitted solution? Hello everyone!
I wanted to know if there exists any way by which we can undo the Accepted submission for a solution which was submitted by me previously at some point of time, or at least make it such that the problem goes to the unsolved section and not in the solved section.
**Reason:** I am using the CF Analytics Extension which basically shows the number of problems solved for each rating range in the form of a bar graph. I noticed that my 800 rated problems solved are too high and it overshadows my other higher rated problems in the graph. This is because I earlier used to solve 800 rated problems to maintain my daily streak and now I regret it heavily when I look at my chart.
For instance, consider the given two graphs:
1. [user:vjudge.7,2024-09-08]
2. [user:Benq,2024-09-08] $\displaystyle orz$
As you can clear...
problem goes to the unsolved section and not in the solved section.
84.
How to Start Competitive Programming from Zero? Hello Codeforces!
-----------------
If you are completely new to Competitive Programming, starting can feel confusing.
You see thousands of problems, unfamiliar algorithms, and people solving problems much faster than you. Sometimes even an easy problem can feel impossible.
So, where should you start?
_“Here are a few things I wish I knew when I started.”_
**1. Learn One Programming Language**
-------------------------------------
First, choose one programming language and become comfortable with it.
If you're starting with **C++**, learn the basics first: _loops, functions, arrays, strings, vectors, and basic STL_. You don't need to master the entire language before touching Codeforces.
Once you know the basics, start solving problems.
**Focus on:**
-------------
- Variables and data types
- Input / Output
- Conditions
- Loops
- Functions
- Arrays
- Strings
- vector
- set
- map
- Basic STL
Don't spend months learning the language before so...
**6. Upsolve Your Unsolved Problems** -------------------------------------
85.
Lesson : Don't panic during contest, if you aren't able to solve easier problem. I would like to share much valuable lesson I learnt today in Div2- 986 contest. I wasn't able to Solve B, and that costs me not solving C and D.
**For anyone, not being able to solve an EASY problem, is more frustrating than not being able to solve HARD problem.**
Chronology:
**1) 2 wrong submissions in B:**
Since 10 ^ 18 * 10 ^ 18 was too large, I wrote of writing code in c++, and convert it to python. [Which Got TLE](https://codeforces.me/contest/2028/submission/290909092) . First wrong submission started panic mode.
Then, I started to find O(1) solution for Problem B, and missed edge cases. Wasn't able to solve B for first 50 minutes of the contest and I couldn't control emotionally.
**2) Read Problem C, found it very easy. Submitted, which failed on Pretest 2**
[I submitted this C,](https://codeforces.me/contest/2028/submission/290932958) during the contest. just by changing one of `<=` condition to `<` gave me AC. I would have easily debugged this, if I ...
solve. Even if I had solved C and D, and left B unsolved during the contest, I
would have been, unsolved during the contest, I would have been satisfied with my performance.
86.
Invitation to October Clash on HackerEarth Hello, and, again, you are invited to a monthly contest: [HackerEarth October Clash](https://www.hackerearth.com/october-clash-15/).
The problemsetter this time is [user:RomaWhite,2015-10-14]; I'm the tester and editorialist. After all, I have to give [user:I_love_Tanya_Romanova,2015-10-14] a chance to compete! :D
The contest takes place this weekend ([starting time](https://www.timeanddate.com/worldclock/fixedtime.html?msg=October%20Clash%20%2715&iso=2015-10-17T01:30:00&p1=64)) and runs for 24 hours. There should be 6 algorithmic problems with partial scoring (points are given independently for passing each test file) and 1 challenge problem. I think the problems are easier than last month, when two subtasks of one problem went unsolved by anyone.
Good luck!
Btw, round 1 of COCI overlaps with this Clash for 3 hours. That, of course, doesn't mean it's not possible to participate in both at the same time — [from my own](https://www.hackerearth.com/january-clash/hof/) [...
subtasks of one problem went unsolved by anyone.
87.
I built a better CPH — and a better Codeforces while I was at it (FREE) **TL;DR -** CPH and Competitive Companion already parse samples and submit for you. CPOS does that too — but that's the boring part. The point is everything *around* it: a **browser companion** that turns the Codeforces page itself into an IDE (write and run your solution right there, plus rating-change predictions, deep profile analytics, head-to-head compare, a focus mode, and a cleaner UI), a **VS Code extension** that — unlike CPH — also renders the problem statement next to your code, and a **terminal app** that actually tells you what to solve next and how to reach your next rating. Free, open-source, MIT, and 100% local — no accounts, no servers, no tracking.
- **Source (MIT):** [github.com/Soham109/cpos](https://github.com/Soham109/cpos)
- **Browser companion (the good part):** [Chrome / Edge / Brave](https://chromewebstore.google.com/detail/gjnbapmjonegeeamdeahcoojgokeogmm) (Firefox source install in the repo)
- **VS Code extension:** [Marketplace]...
**Recommendations that are actually about you.** It looks only at *unsolved*
problems near your, unsolved problems to get there. Press Enter on a step to start solving it.
88.
The Problem Was Easy, But I Still Couldn't Solve It Sometimes I open a Codeforces problem, look at its rating, and think:
> *"This should be easy."*
Then, 30 minutes later, I'm still staring at the screen.
The funny part?
Sometimes the solution is actually simple.
So why couldn't I solve it?
Recently, I've started realizing that there is a big difference between:
> **Knowing a concept**
and
> **Recognizing when to use it.**
For example, I might already know about:
* GCD
* Sorting
* Prefix sums
* Binary search
* Two pointers
But when a problem doesn't explicitly tell me which technique to use, everything suddenly becomes harder.
## Reading the Solution Feels Easy
This is something I find interesting.
After failing to solve a problem, I read the editorial and think:
> *"Oh... that's it?"*
The solution suddenly looks obvious.
But if I had never seen the editorial, I might have spent another hour without finding that idea.
**Understanding a solution after seeing it and finding tha...
Every unsolved problem can reveal something that I need to improve.
89.
Cofo PH & PC for codeforces and atcoder ! [Cofo PH & PC (Cofo Problem hider and problem chooser)](https://github.com/Cofo-admin/Cofo_ph_pc)
Download it from [Github](https://github.com/Cofo-admin/Cofo_ph_pc).
Cofo problem hider and problem chooser : hide solved problems in codeforces problemset page !!!!! and randomly choose problems with rate that you say that you dont solved it yet !!!e
use "Load Unpacked" to install it !
Install the chrome extention and once Enter your UserName and change theme between black and white
Enter two numbers then extension will choose a unsolved problem between the numbers and open it in a new tab !
note : if you don't enter your username the extention will suggest a random problem and dont care about you solved it or not!
Now no need to explore problemset page for a new problem just enter 2 numbers !!!!!
<img src="http://uupload.ir/files/2nea_screenshot_(354).png">
<img src="http://uupload.ir/files/3rsi_screenshot_(355).png">
And the second feature [hide unsolved ...
Enter two numbers then extension will choose a unsolved problem between the
numbers and open it, And the second feature [hide unsolved
problems](https://codeforces.me/blog/entry/79656) in, Enter two numbers then extension will choose a unsolved problem between the
numbers and open it in
90.
Cost-Benefit Flow ## Motivation
By chance, I stumbled upon the blog post by [user:errorgorn,2025-11-22] titled [Solving Problems with Min Cut Max Flow Duality](https://codeforces.me/blog/entry/136761). When they mentioned using flow (for certain problems) in a similar way to 2SAT, something clicked for me. While I knew how to solve a variety of flow problems along with forming certain flow networks ad hoc, there was this entire subset of flow problems which I previously did not understand how to do.
The blog post does a great job of explaining many of the concepts/applications, but there were certain things that got black-boxed. In order to understand things, my brain works such that truly understanding what is going on under the hood (often through proofs) helps me better intuit how to use ~~and abuse~~ a tool. Naturally, I tried to search the internet for more information on this topic. Unfortunately, I quickly came to realize that not much material as in-depth as the aforementioned blog p...
solved a problem that has been left unsolved for half a century and a $1
million check will be showing up
91.
LeetCode Amazon interview problems **LeetCode** FAANG interview problems solved | [LinkedIn post](https://www.linkedin.com/posts/mohamed-samir-9b0b2a203_programming-leetcode-coding-activity-7212762595429085185-7PHy?utm_source=combined_share_message&utm_medium=member_desktop)
Excited to share a valuable resource for all job seekers targeting big companies! This Google Sheet, created by me, is tailored for those preparing for interviews at major firms.
**Amazon Interview Problems Sheet**
- [Sheet link](https://lnkd.in/ddAZPvWt)
- [GitHub repo](https://lnkd.in/dfr6dSdt) </p>
**What’s Inside:**</p>
- **Amazon** Company-Wise Questions from **LeetCode**, snapshot of interview questions from 2022
- Well-categorized based on difficulties, solved/unsolved, and premium/non-premium
- My solution link is attached to the sheet (if I have already solved the problem , stay tuned for more upcoming solutions)
If you have **LeetCode Premium** and want to **contribute** by adding newer snapshots, please re...
- Well-categorized based on difficulties, solved/unsolved, and
premium/non-premium, -categorized based on difficulties, solved/unsolved, and premium/non-premium -
My solution link is
92.
ProjectEuler+ I'm quite sure some of you have ever participated in a HackerRank contest. And after going to "Compete" page and seeing "ProjectEuler+" as an active contest for about several months or even years you could have wondered "How can it be for so long"?
ProjectEuler is a well-known website with no need for advertising. So, instead of describing countless beautiful features of it, I'd better tell some of its disadvantages for me as a competitive programmer. You see, in my humble opinion, there is no honor in boasting "Oh, my program runs in just two minutes on my modern laptop" when it's possible to write the same program which runs in several milliseconds.
That's why ProjectEuler+ exists. At first glance, you see the exact same statement, but then... multitest? And constraints ten or even thousand times bigger than they were in original problem? And time limit is just a couple of seconds? Well, such rules seem to be more familiar to us.
I wanted to write this blog a month later whe...
but recently a problem was created that stays unsolved for a week — the first
time we have, stays unsolved for a week — the first time we have such problem. So, I invite
everyone to
93.
Mastering the Art of Competitive Programming: A Roadmap to Success **Introduction:**
Competitive Programming (CP) is more than just solving problems; it's a journey of continuous learning, improvement, and mastering the art of algorithmic thinking. Whether you're a beginner or an intermediate coder, this blog aims to guide you through the steps to become proficient in Competitive Programming.
**Understand the Basics:**
Before diving into complex algorithms, ensure you have a solid understanding of the basics of programming languages, data structures, and algorithms. This forms the foundation for advanced problem-solving.
**Choose the Right Language:**
Select a programming language you are comfortable with and one that is widely accepted in the CP community. Common choices include C++, Python, and Java. Familiarity with your chosen language is crucial for efficient problem-solving.
**Explore Data Structures:**
Master essential data structures like arrays, linked lists, stacks, queues, trees, and graphs. Understanding when to use each struc...
contest, spend time on the unsolved problems, understand the solutions, and
learn from the experience.
94.
CF Statistics Hello Codeforces community!
Me and my friend [user:nakamura,2018-07-22] developed [CFStats](https://cfstatistics.herokuapp.com): a website that allows stats comparison between 2 Codeforces handles.
The comparison includes:
- Rating graph comparison over the time (just like in Codeforces, but for 2 users)
- All attempted (but unsolved) problems by each handle
- Problems solved by tag by each handle
- Unique problems solved by each handle
- Problems that both handles solved
- Contests that each user participated
- Contests in which both handles participated (and their respective positions)
And we will be more than glad to introduce more features! We are open for your suggestions :)
Also, CFStats lets you create a profile. There, you can save:
- Codeforces friends (so you can easily compare yourself to them with one click)
- Problems to solve later
- Contests to solve later
The advantage of saving such things is that every time your profile is updated a mess...
(but unsolved) problems by each handle - Problems solved by tag by each handle
- Unique problems, , but for 2 users) - All attempted (but unsolved) problems by each handle -
Problems solved by tag by
95.
Python Codeforces API Wrapper library Hi there!
I would like to introduce wrapper [library](https://github.com/soon/CodeforcesAPI) for Codeforces API written in Python 3. It helps you with collecting, analyzing and visualizing data.
####Intro:
As a contest member you may want to increase your power by solving problems, but some of them are quite simple, and you want to skip them. Lets say, you want to practice only Div2-C problems. You could, of course, open Problemset, then press `Ctrl+F` and write `C` to highlight preferable problems. But this may take a long time (you should look through the page and open only unsolved Div2 problems. A little boring, neh?).
Another way is write a script for loading all problems then filter only unsolved Div2-C problems and sort by solved count. Sounds interesting, isn't it? There is an [example](https://github.com/soon/CodeforcesAPI/blob/examples/examples/show_only_unsolved_problems/main.py) of such script. All you need is run it and input your codeforces handle, and it w...
. But this may take a long time (you should look through the page and open only
unsolved Div2 problems, unsolved Div2 problems. A little boring, neh?). Another way is write a script
for loading all
96.
Similar Problems Webservice Hi Guys,
Many times, when we look at the solution for an unsolved problem or love a specific problem, we might want to try out a problem similar to it. Currently we can only search problems only based on tags. But from now on we can just input a problem and get a list of problems similar to it. We can query here [similar_problems](https://codeforces-similar-problems.herokuapp.com/)
Example :
After Submitting,
Here,
- Problem Name is just the contestId + index. eg (1389A),
- We can also specify the rating range which is the problem difficulty rating range within which we want out similar problems to be. If nothing is specified, by default it will consider problems rating between -500 to +500.
Currently, I am computing cosine similarity between two problem's tags. Yes, this is the most basic method which we can think of and obviously there are many false...
Hi Guys, Many times, when we look at the solution for an unsolved problem or
love a, Many times, when we look at the solution for an unsolved problem or love a
specific problem, we
97.
CodeCraft IIIT Hyderabad(Programming Contest) Hi,
I am happy to extend you to the invitation to participate in annual programming contest of IIIT Hyderabad. It's an ACM style programming contest, except that it's for individuals and not teams.
You will have a chance to devour some really nice(hopefully!) problems. I think considering the wide difficulty levels in problems everyone will find some interesting/challenging problems to solve.
It begins on 25th Jan, 2015 at 1400 IST.
To see time in other time zones: http://bit.ly/1u8sdBI
Visit http://felicity.iiit.ac.in/threads/codecraft/#content for rules.
Register here: http://felicity.iiit.ac.in/register/
Join facebook event page here for further notifications: https://www.facebook.com/events/378291325683458
Also, there will be some attractive prizes for winners(to be announced soon).
By the way, here's the leaderboard for last years contest:
<a href="http://i.imgur.com/B4PJOtT.png"><img src="http://i.imgur.com/B4PJOtT.png"/>...
" /> Just like last year, 1 problem went unsolved. But, we'll be accepting
solutions, ://i.imgur.com/Jiwre15.png" /> Just like last year, 1 problem went unsolved.
But, we'll be
98.
Practice Forcius - a Chrome extension to quickly pick up an unsolved problem. Hi there!
Have you ever find yourself too lazy to open codeforces, find a problem and start solving it, even if you have free 10 minutes? I have. All the time. This isn't something I'm proud of, and I decided to motivate myself somehow, therefore I created a chrome extension which allows you to select a random unsolved problem in a single click.
To make things interesting, it also starts a timer, so you can practice solving tasks faster. And if you're lucky enough to solve the problem in time, you'll receive a special gift — notification!
You can download the extension here: [Chrome Extensions Store](https://chrome.google.com/webstore/detail/practice-forcius/cljnoaoppgbpdpcekmcaebiendookeac).
This is a beta, so your feature requests and bug reports are very welcome here: [Github]( https://github.com/soon/practice-forci...
Practice Forcius - a Chrome extension to quickly pick up an unsolved problem., random unsolved problem in a single click.
99.
Pisano Period of Large Numbers Hi, hope you all have a good day (or a good night, it's midnight in my area lol).
Recently I came across a problem, which takes two integers — **n** and **m** — as input, with `3 <= n, m <= 10^9`. The problem asks for the value of `F(F(i)) mod m`, with `F(i)` denoting the `i`-th Fibonacci number.
I'm not sure if this question has been asked before on any platform (though I'm pretty sure no one has asked about it on English Competitive Programming Forums), but this seems to be a direct application of the Pisano Period. However, I am only able to find an `O(m^2)` algorithm, which does not suffice the condition of this problem. Even though there seems to be a fast enough algorithm on [mathoverflow](https://mathoverflow.net/questions/144308/calculating-pisano-periods-for-any-integer), the writer explicitly stated that this algorithm may fail with specific prime numbers. So, my question is does there exist a **precise** method of calculating the pisano period of large number `...
. **Update**: The problem of precisely calculating the pisano period for every
number is in factunsolved, unsolved, since the existence of numbers that potentially break the properties
are not yet proved.
100.
NITS Hacks 5.0 Finals Mirror Contest Hello Everyone,
After successful completion **NITS Hacks 5.0**, we would like to make the problems of **NITS Hacks 5.0 Finals** public through a mirror contest. Anyone can participate in it individually or in a team of 3 members.
**Number of Problems:** 9 (not sorted by difficulty)
**Contest Duration:** 3.5 hours
**Contest Time:** 27th October, 6 pm to 9:30 pm IST
**Contest Link:** https://codeforces.me/contestInvitation/94509f62591f76afe546707ad1c471829412c9f5
Two problems remained unsolved during the contest.
I would like to see someone solving them during the mirror contest.
Finally, I'd like to thank my friends [user:jo3kerR,2022-10-26], [user:jac_nikola,2022-10-26], [user:noobabhi,2022-10-26], and [user:agarwala2512,2022-10-26] for coming up with such interesting problem ideas, and my seniors [user:amit_dwivedi,2022-10-26], [user:invictus_123,2022-10-26], and [user:harshit15,2022-10-26] for testing the problems.
I hope you all would love the problems....
remained unsolved during the contest. I would like to see someone solving them
during the mirror, Two problems remained unsolved during the contest. I would like to see someone
solving them
101.
17 Free AI Battle - Qualifier Round Finished! For Chinese Version, click [this](https://www.luogu.com.cn/article/uutv85wp/)
**Special thanks to Codeforces for the evaluation resources!**
To avoid any suspicion of cheating, I used problems I have already ACed for testing.
~~I don't think Doubao can pass the second round (~~
Each AI gets one revival chance (unless it does nothing or cannot be used for free)
# Round 1
Let's start with an easy *800 problem!
[CF2248A](https://codeforces.me/problemset/problem/2248/A)
It's a super simple greedy problem, both players obviously delete from the very front.
| AI/Agent Model | Status | No. |
| :--- | :---: | :--- |
| \*chatgpt | **Accepted** | 1 |
| \*claude | **Accepted** | 2 |
| \*Grok | X. No Response. | 3 [Out]() |
| \*deepseek | **Accepted** | 4 |
| \*perplexity | X. *Wrong Answer on test 1* | 5 [Restart]() |
| Gemini 3.5 Flash-Lite | **Accepted** | 6 |
| Qwen 3.7 | **Accepted** | 7 |
| Doubao | **Accepted** | 8 |
| Baidu Wenxin Yiyan | **Accepted** ...
| X. None. Unsolved. | 11 | | Kimi K2.6 |
[**Accepted!**](https://codeforces.me/contest/689
102.
What to do if you've reached Candidate Master in 2025 <a class="rated-user user-violet">Candidate Master</a> is a rank after <a class="rated-user user-blue">Expert</a> and before <a class="rated-user user-orange">Master</a> that represents a smooth transition between these two ranks. Its meaning to the community is that you're more than a competitor and you're invested in the platform. People will now recognize you more and take you more seriously. Of course, you'd expect that purple color you got gives you more perks. Well, look no further because I've written some stuff that may interest you, that's accessible once you become <a class="rated-user user-violet">CM</a>.
[cut]
Getting to Candidate Master is no joke. My first ever Codeforces competition was [Round 885](https://codeforces.me/contest/1848), which was more than two years ago. Given my background in CP I got to Expert in only 9 competitions, but then I stayed for over a year in that layer because Codeforces competitions simply have different tasks from local competitions...
every moment of the competition make sure to have the first two unsolved tasks
read. It will give you
103.
Coderforces Web Tool for Finding Unsolved Problems of Multiple Handles I made a codeforces web tool where you can add **multiple** handles and select problem **rating** and it will give you **unsolved** problem links of those handles of that particular rating . It should give correct data.If you guys find any bug in data let me know , I will fix it
[website link](https://finitemoves.pythonanywhere.com)
**It is particularly useful for people who have multiple accounts and for people who want to make a practice contest for multiple people**
Coderforces Web Tool for Finding Unsolved Problems of Multiple Handles, ** and it will give you **unsolved** problem links of those handles of that
particular rating . It
104.
Just Solve a Problem (Chrome Extension) Hello Codeforces!
Like many of you, whenever I sit down to practice, I often spend 10–15 minutes just wandering through the problemset page, applying filters, avoiding already solved problems, or getting spoiled by topic tags before even reading the statement.
To solve this decision fatigue, I built a lightweight Chrome extension called **Codeforces Problem Suggester**.
---
### What does it do?
It injects a native **"Just Solve a Problem"** box directly at the bottom of any Codeforces profile page, offering an instant, rating-targeted unsolved problem recommendation.
---
### Key Features
* **Rating-Adaptive Recommendations:** Automatically reads the profile's current rating and calculates a recommended target window ($[x, x + 200]$), clamped strictly within the official $800 - 3500$ rating range.
* **3 Practice Modes:**
Warm-up: $[x - 200, x]$,
Standard: $[x, x + 200]$,
Hard: $[x + 200, x + 400]$, where x is your current rating rounded to the next ...
page, offering an instant, rating-targeted unsolved problem recommendation.
105.
Bug: Unable to Hide Unsolved Problem Tags Is anybody else also having the issue where they are unable to hide tags for unsolved problems? I uncheck the checkbox in the problemset tab but after some time has passed or after I have refreshed the page, the change is reverted and the tags are visible once again. This has been happening to me for more than a week now.
[user:MikeMirzayanov,2018-02-26], can you look into this?
Thanks!
**UPD** — The bug has not been fixed yet.
**UPD 1-3-18** — The bug has not been fixed yet.
**UPD 3-3-18** — The bug lives on.
Bug: Unable to Hide Unsolved Problem Tags, Is anybody else also having the issue where they are unable to hide tags for
unsolved problems? I
106.
17 Free AI Battle - Qualifier Round Finished! For Chinese Version, click [this](https://www.luogu.com.cn/article/uutv85wp/)
**Special thanks to Codeforces for the evaluation resources!**
To avoid any suspicion of cheating, I used problems I have already ACed for testing.
~~I don't think Doubao can pass the second round (~~
Each AI gets one revival chance (unless it does nothing or cannot be used for free)
# Round 1
Let's start with an easy *800 problem!
[CF2248A](https://codeforces.me/problemset/problem/2248/A)
It's a super simple greedy problem, both players obviously delete from the very front.
| AI/Agent Model | Status | No. |
| :--- | :---: | :--- |
| \*chatgpt | **Accepted** | 1 |
| \*claude | **Accepted** | 2 |
| \*Grok | X. No Response. | 3 [Out]() |
| \*deepseek | **Accepted** | 4 |
| \*perplexity | X. *Wrong Answer on test 1* | 5 [Restart]() |
| Gemini 3.5 Flash-Lite | **Accepted** | 6 |
| Qwen 3.7 | **Accepted** | 7 |
| Doubao | **Accepted** | 8 |
| Baidu Wenxin Yiyan | **Accepted** ...
| X. None. Unsolved. | 11 | | Kimi K2.6 |
[**Accepted!**](https://codeforces.me/contest/689
107.
Hiding problem tags when adding problems to mashup As we all know, Codeforces has a feature that allows users to hide problem tags for unsolved problems. However, when I create a mashup contest, it shows the tags even for unsolved problems.
It is a very minor issue, but it would be better if the "hide tags for unsolved problems" also includes hiding tags when adding problems to mashup contests. Just imagine being spoiled by the "ternary search", "2-sat", "meet-in-the-middle" tags right away before reading the problems.
As we all know, Codeforces has a feature that allows users to hide problem tags
forunsolved, It is a very minor issue, but it would be better if the "hide tags for unsolved
problems" also
108.
Upsolving — TJU / Codeforces Tool Hi,
As most users know, upsolving is very important to improve in programming contests, sometimes you tried to solve a problem without luck, while seeing the same problem after some time (days / months / years?) you may be able to solve it, this means you improved the required skills to succeed this problem.
I tried to find all my unsolved problems from Codeforces without luck, in PROBLEMSET there is a frame (Last unsolved) with the list of the last 15 problems tried but that's not enough.
I checked the Codeforces API to find a way to check all my unsolved problems without luck, so I wrote a crawler to find them all, the project is on github: https://github.com/AlexITC/upsolving/
This tool uses your login details and extract the unsolved problems from Codeforces Rounds and from the Gym.
I hope this can be helpful.
P.S: If someone knows how to retrieve this information using Codeforces API, let me know please.
P.S.2: There is an unknown reason why all tried problems...
this problem. I tried to find all my unsolved problems from Codeforces without
luck, in, I checked the Codeforces API to find a way to check all my unsolved problems
without luck, so I, I tried to find all my unsolved problems from Codeforces without luck, in
PROBLEMSET there is a, This tool uses your login details and extract the unsolved problems from
Codeforces Rounds and from
109.
New Features on Clever Code [Clever Code](https://clever-code.vercel.app/)
==================
Hello everyone!
Just a update of [Previous blog](https://codeforces.me/blog/entry/133285) <br>
If you’ve been using Clever Code, first of all — Thank you!
You already know how helpful it is for analyzing and comparing Codeforces problem-solving history. But today, I’m thrilled to share some exciting news and a major update with you.<br>
Recently, I logged into my Vercel dashboard just out of curiosity, expecting maybe one or two users here and there. But what I saw completely surprised me — Clever Code had over 2000 edge requests in the last 30 days, coming from multiple countries! <br>
I genuinely didn't expect this kind of reach — it started as a personal tool, and now it's being used globally. So I thought:
" If people are actually using and benefiting from this, I should definitely take it to the next level."
And that’s exactly what I did.
. Let $f_i$ be be number of occurrence of sub-strings $S_i$ with $1 \le i \le k$.
Find the total $F = \sum_{i=1}^k f_i^2 \mod{M}$ in which $2 \le M \le 10^9$.
There are $T \le 50$ tests and each test includes string $S$ and number $M$.
Example:
**input:**
~~~~~
2
zoo
10
@#$%
1000000
~~~~~
**output:**
~~~~~
2
16
~~~~~
#### **Problem 2.**
Let $(a_n)$ be a positive integer sequence and a key $X$ be a positive number. Count the number of ordered triples $(i,j,k)$ such that $a_i+a_j+a_k \ge X.$
There are $T \le 50$ test and each test includes ...
problems remaining unsolved during this contest. Hope some one can help me
with the outline idea
112.
How AI glorifiers aren't being recognised by anti-cheat measures. Let us for a moment, keep aside the fact that it is usually easily recognizable from the code itself whether it is self thought or AI generated. Have a look at the image of submission of a user [user:pranotiaaryan,2025-07-01] from "Educational Codeforces Round 180 (Rated for Div. 2)"
Pretty usual submission stat, isnt it?
No!
First, second and third submission, simple, no suspicion
Fourth question: First incorrect attempt : 20:52.
Second incorrect attempt: 21:02.
Third incorrect attempt : 21:12.
Seems like AI tools couldnt figure out the correct approach. No worry, lets move onto the next question (question E)
As I am a legend which even Masters and Grandmasters aren't, I am able to figure out the approach to the question E in mere 6 minutes. Not to forget this 6 minutes include thinking as well as typing the code.
Unfortunately, I am still 'human', so code co...
previous unsolved question, change the code and hurray! chatgpt, oops! my
brain worked.
113.
Performance Analysis Graphs Hello community,
I've recently added new graphs on the CodeSync website, like Question Rating vs. Average Time Taken During Contest, Questions Solved Count vs. Rating , etc. Below are some screenshots showing how they look based on my Codeforces ID:
If you're interested, simply type your Codeforces handle and click enter. Here's the link to the website:
https://code-sync-sandy.vercel.app/graphs
You might also want to explore the CodeSync website itself. It's a platform where you can simulate virtual contest-like environment with questions fetched based on your input. It's great for Team Contests (as it fetches common unsolved questions), virtual contests, and even for practice.
...
Contests (as it fetches common unsolved questions), virtual contests, and even
for practice., for Team Contests (as it fetches common unsolved questions), virtual contests,
and even for practice
114.
CodeForces new feature request Hello CodeForces,<br>
I'd like to propose a new (minor) feature. As we all know, we can set the visibility of tags for unsolved problems by going to problemset and then checking or unchecking the "Show tags for unsolved problems" checkbox.<br>
When solving problems, if I don't have an idea of the solution, I sometimes may take a look at the tags to give me some hints. However, this can get pretty annoying. When I want to show problem tags, I then have to go to problemset, check the checkbox, and then reload the page. The only option to avoid this is to show problem tags for all problems, but this causes me to sometimes get a peek at the tags before I really need to.<br>
As a solution, I propose that users are given the option of hiding/showing a problem's tags on the page of the problem. To be more exact, you can set the default visibility of tags on the problemset page. Then, when visiting a problem, the tags will be shown/hidden based on your default setting. You then can show/hid...
visibility of tags for unsolved problems by going to problemset and then
checking or unchecking the
115.
Weekly Training Farm 25 Hi everyone!
I would like to invite you to the Weekly Training Farm 25 !! The problemsetter is me ([user:dreamplay,2017-02-26]) and the tester and quality controller is [user:dreamoon,2017-02-26]. Big thanks to [user:drazil,2017-02-26] for his help in preparation.
It will be a 2 hour — 5 problems contest, with ACM-ICPC style scoring, will be held on codeforces, 1.5 hours after CF round #402.
Contest time: [17:00 UTC + 5.5](https://www.timeanddate.com/worldclock/fixedtime.html?day=26&month=2&year=2017&hour=14&min=30&sec=0&p1=166)
<br>
[Contest link](http://codeforces.me/group/gRkn7bDfsN/contests): Join the group (as participant) first and find Weekly Training Farm 25.
Editorial will be provided right after the contest.
<br>
Here are the [standings](http://codeforces.me/group/gRkn7bDfsN/contest/211128/standings/groupmates/true) from a recent Weekly Training Farm contest.<br><br>
Good luck and hope you enjoy the problem solving!
UPD: 30 min to the start !!
...
Sadly, last problem went unsolved. Happy upsolving.
Editorial will be posted soon.
116.
Some Useful chrome extension for codeforces 1. [Carrot](https://chromewebstore.google.com/detail/carrot/gakohpplicjdhhfllilcjpfildodfnnn) predicts rating change and analys performance.
2. [CF Analytics](https://chromewebstore.google.com/detail/cf-analytics/hhljbjodjdbjbggddjaidojnlmaobcpo) Analyse profiles. Include statistics of problems solved. A bar chart showing problems solved for each problem rating, a doughnut chart displaying tags solved across any problem and also lists a count for each tag. The ‘Unsolved Problems’ shows a count of all problems attempted with not correct verdict and also lists them.
3. [CF Tracker](https://chromewebstore.google.com/detail/cf-tracker/hadiffebpglmdnknojeoelfgmjleiecc) keeps track of spent time on a particular problem.
4. [Codeforces Practice Tracker](https://chromewebstore.google.com/detail/codeforces-practice-track/cnahgdhboflcnojgmeehhhfeoojifonm) you can Read overview section of this extension.
**Bonus:**
[Dark Reader](https://chromewebstore.google.com/detail/dark-r...
count for each tag. The ‘Unsolved Problems’ shows a count of all problems
attempted with not, tags solved across any problem and also lists a count for each tag. The ‘
Unsolved Problems’ shows a
117.
Unsolved problem — just sharing Here is a problem I thought of. This is just for others' interest, maybe to help them pass the time.
I thought of this problem initially because I wanted to put it in a contest, however it turned to be too hard for me and a few others so it shouldn't be in a contest:
you need to construct a permutation of length N. you're given M pairs of integers (each pair contains 2 distinct elements, both are between 1 and N).
the permutation you construct needs to have the following value minimized:
for each pair {X1, X2}, add up to the total sum the distance (indicies distance) between the values {X1, X2}.
you can print any correct answer is multiple ones exist.
~~~~~
input:
N M
M pairs, described in the statement
output:
the minimized value described in the statement on the 1st line, and the permutation on the 2nd one.
examples:
input:
3 2
1 2
3 1
output:
2
3 1 2
input:
4 4
1 2
4 2
3 1
3 4
output:
6
2 1 4 3
~~~~~
Unsolved problem — just sharing
118.
Codeforces Viewer Hello guys, as a coding challenge in lockdown, I have created a website for Codeforces problem set viewing. Its primary function is to filter problems in problems-set based on some parameters like the difficulty of the problem, rating min, rating max, tags, etc. It has some other functions also like a link to other users attempted but unsolved problems, random problem suggestor based on your rating, etc. I hope everyone likes it. CFViewer is my first web development project.
**Link**: [rudradesai.in/cfviewer](https://rudradesai.in/cfviewer)
Also if you feel like any functionality is missing, then please write it to me on [[email protected]](mailto:[email protected])
Any feedback, positive or negative, is welcome. Thank You!!
Update 1: Added new functionalities, now you can try a random unattempted contest, see all the contest on code forces with an added feature of attempted or not. Also, you can view submissions and problems for each attempted contest.
And o...
like a link to other users attempted but unsolved problems, random problem
suggestor based on your
119.
Last unsolved sidebar block has a bug Hi everyone!
When I try to open a acmsguru problem from last unsolved it says "No such contest" and returns to the last page I was on.
It's because last unsolved link for sgu problems is https://codeforces.me/problemset/problem/99999/{ID}
But there is no such page. it should be https://codeforces.me/problemsets/acmsguru/problem/99999/{ID}
[user:MikeMirzayanov,2022-02-05] can you fix this?
Thanks
Last unsolved sidebar block has a bug, Hi everyone! When I try to open a acmsguru problem from last unsolved it says
"No such contest, It's because last unsolved link for sgu problems is
https://codeforces.me/problemset/problem/99999, When I try to open a acmsguru problem from last unsolved it says "No such
contest" and returns to
120.
HackerEarth Collegiate Cup Second Elimination Results Hello Everyone,
Last week we conducted HackerEarth Collegiate Cup Second Elimination Round. Here is the screenshot of the LeaderBoard.
There were 10 problems to be solved in 5 hours. Jinotega managed to solve 9 out of 10 problems and secured the first position. One problem remained unsolved. 15 teams got selected from India and 5 teams got selected globally. Just for fun, the last team that got selected from India for the Final Round is named **alwayslast**. :)
Top 5 Global teams who got qualified for the Final Round are:
1. Jinotega: Moscow Institute of Physics and Technology
2. demonteam: Moscow State University
3. VietAnplusplus: Ho Chi Minh City University of Science
4. Frogless: Kiev National Taras Shevchenko University
5. lovesubcul-Team: University of Tsukuba
Top 5 Indian teams who got qualified for the Final Round are:
1. FacelessMen: Indian Institute o...
secured the first position. One problem remained unsolved. 15 teams got
selected from India and 5
121.
ACM/ICPC China Final 2016 Live
- 14:00 : The contest is end!
- 13:00 : The scoreboard is close.
- 12:58 : While [user:TooDifficuIt,2016-12-11] and [user:WJMZBMR,2016-12-11] debugging on the Math problem, [user:jcvb,2016-12-11] start the Geometry.
- 12:55 : It seems that THU Deep Dark Fantasy is working on the Math problem. They are very close with the right solution, but currently failed on the sample. SJTU Absolute Weapon* is working on problem J, and everything looks right but failed on the sample too.
- 11:41 : THU Deep Dark Fantasy solve problem J.
- 11:07 : [user:TooDifficuIt,2016-12-11] is working on implement a network flow, seems that they are on problem J. [[pic.](http://www.shuizilong.com/house/wp-content/uploads/2016/12/Screen-Shot-2016-12-11-at-11.07.21-AM.png)]
- 11:01 : Joke, some team use a function named "fxxk" during the livetream. [[pic.](http://www.shuizilong.com/house/wp-content/uploads/2016/12/fxxk.jpg)]
- 10:50 : THU Deep Dark Fantasy solve G and F, they are still 2 problems ahea...
ahead. - 10:17 : XJTU Peach solve problem F, only 3 problems remain unsolved
at this moment, a.k.a, . - 10:17 : XJTU Peach solve problem F, only 3 problems remain unsolved at this
moment, a.k.a, a
122.
DEVSKILL CODING CONTEST 20 Hello Codeforces Community,
I am glad to announce that there will be [DEVSKILL CODING CONTEST-20] (https://www.devskill.com/NewContest/ContestDetail/0fef9d09-fcb7-cb96-6a03-08d58fa46501) on [30th March, Friday at 10PM(UTC+6)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=CODING+CONTEST+20&iso=20180330T22&p1=73&ah=2&am=30) in [Dev Skill](https://www.devskill.com/).Basically, Dev Skill is a Bangladeshi contest site which arranges two contests every month (one easy contest for beginners and another for everyone ).
This contest will consist of 6 problems and you will be given 2:30 hours to solve them all.
The score distribution for this contest is: `500 - 800 - 1200 - 1500 - 1800 - 2000`
The problems were written and tested by [user:feodorv,2018-03-28], [user:fsshakkhor,2018-03-28], [user:khatribiru,2018-03-28], [user:mahmud2690,2018-03-28], [user:math10,2018-03-28] and [me](http://codeforces.me/profile/BishalG)
We're inviting you all to join us in this contest...
were unsolved at that time.
123.
The art of understanding Editorial and Upsolving It's almost a year I am in competitive programming, doing problems here and there. I realized that I have to solve problems to be good at this. Now what happened to me repeatedly is this-
~~~~~
1. Be in a virtual or actual contest.
2. Try hard.
3. I can only solve 1 or 2.
4. Contest ends.
5. Check the editorial for unsolved ones.
6. **Can not understand the idea or feel confident enough to solve the problem.**
7. Try an hour to understand.
8. Leave it...
~~~~~
I have found that for this reason I an still green and I have to write this. In case of practice problems I take this approach
~~~~~
1. Read the question.
2. Understand and try to solve.(I try exactly for 10-15 mins..)**(Is this correct or should I try longer?)**
3. If I can't solve then I read the editorial.
4. Can not understand the idea or feel confident enough to solve the problem.
5. Try an hour to understand.
6. Leave it...
~~~~~
The problem is similar here also.
#### My question is
...
ends. 5. Check the editorial for unsolved ones. 6. **Can not understand the
idea or feel
124.
Pupil in 80 days - Day 16,17 ### Hello Codeforces!
I didn’t write this blog yesterday, because yesterday I decided to take a little rest, especially after the events of the recent Div.4 and the cluttering of the site with similar blogs. Today I was able to solve the problems from the archive, but to be honest they were easy. About the recent Div.4: I still can't understand how I couldn't solve E, because it was very easy, but even so, thanks to this contest, I set a new high point in my rating. Despite this, I made a very big mistake(violating rules), which probably greatly affected my credibility.
At today's contest I couldn't solve B, the reason for this was probably that I overloaded my head a lot before the contest today, and so now I can't come up with another idea for solving it. Also today I solved 100 problems on CF since I started using it.
#### Plans for tomorrow:
Finish today's contest, pass the mashup from the coach, complete unsolved problems from the archive and practice the topics that I h...
Finish today's contest, pass the mashup from the coach, complete unsolved
problems from the archive
125.
An interesting problem Hello everyone, I hope you all are doing well.
I wanted to post a question, which I am unable to solve. I even gave that problem to some of my CM friends and yet it remains unsolved. Hence, I thought it is a good time to put it up on the community :). So the question goes like this:
There are N Base-Stations (BS) and P users. jth BS allocates Cj resources per packet. If the user i connects to BS j, he gets Rij number of packets. User, i can connect to a limited set of BS given by the set Ui.
All the entries of Cj, Rij are non-negative. You know the vector {Cj} (1<=j<=N), 2D-matrix {Rij} (1<=j<=N,1<=i<=P), set of sets {Ui}.(You can basically remove the importance of Ui's completely by tweaking the Rij matrix as explained below)(Please see the example for more clarification)
You need to allocate **all** the users **to exactly one BS** of their own. (Please see the example for more clarification). You need to find an allocation such that, the sum of average resource allocated...
friends and yet it remains unsolved. Hence, I thought it is a good time to put
it up on the
126.
CSES Friends Solver — A Chrome Extension to see which friends solved a problem Hi Codeforces,
I built a small Chrome extension called **CSES Friends Solver**. I know there are already extensions out there for CSES, but I couldn't find any that specifically told you whether your friends have solved a particular problem. So I made one.
When you open any CSES problem page, a small box appears showing which of your friends have solved that problem and which haven't. Solved friends show a green check and appear at the top, unsolved ones show a red cross.
Setup is simple. Click the extension icon, enter a display name for your friend and their CSES user ID (the number you see in their profile URL like cses.fi/problemset/user/264530/), and you are done. The extension handles the rest automatically whenever you visit a problem page.
You can find it here: [CSES Friends Solver](https://github.com/bhaviksharmawork/cses_friends)
If you have any suggestions or want to contribute, PRs are...
that problem and which haven't. Solved friends show a green check and appear
at the top,unsolved
127.
Codeforces Visualizer Android App Hi, this is my very first post on codeforces.
I have made an application using codeforces api. It's available in Google Play store. It can be found here https://play.google.com/store/apps/details?id=com.codeforcesvisualizer
In this app you can :
- View upcoming contest list
- View previous contest list
- Analyze single user profile
- Language chart, tags list, unsolved list and other charts are available
- You can compare two users using their handle
- From contest list you can directly go to contest page
Please, give it a try.
If you find any kind of bug, please let me know so I can fix it.
If you have any idea of feature that can be useful, please let me know. I will try to add it.
Here are some screenshots of the application-
![ ](https://lh3.googleusercontent.com/9G4tcS-0guJvHoy2xFEKy2_e0y6LovmTLUBIHuJbnCZw5VIJIfmHOmIfIVr6BgBikg=w720-h310-r...
- Language chart, tags list, unsolved list and other charts are available -
You can compare two users using
128.
Filtering by tags affects disabling 'show tags for unsolved problems' checkbox. Hello everybody!
Before, when I was filtering the problemset table by some tag while _show tags for unsolved prolems_ checkbox was disabled, the page was showing me the problems that I had solved and been tagged with that tag.
Now it shows all the problems with the filtering tag, but without showing _literally_ the tags beside the names of problems :p.
I think this was not intended, and, anyway, IMO, this defeats the purpose of that checkbox. So, please, return to that past version of this point.
Thanks in advance!
Filtering by tags affects disabling 'show tags for unsolved problems' checkbox., for unsolved prolems_ checkbox was disabled, the page was showing me the
problems that I had solved, Before, when I was filtering the problemset table by some tag while _show tags
forunsolved
129.
Avoiding problem tags in practice I had been facing this problem from quite some time. Suppose I want to practice the D problems of all recent contests or any particular problem of some contest. So whenever I would open the problem, the tags would be visible to me which I don't want because I want to think about the problem from scratch. The only solution I saw was to make it a virtual contest and then do the problem. But this also has downsides because maybe I would like to read the problem now and then open it again tomorrow for some clarification. Then I would have to start a virtual contest each time I want to view the problem.
Now I use the "Complete problemset" link located below the problems on the right side (wonder why I didn't notice this earlier) which enables me to view all problems without constantly trying to not look at the tags. I hope this helps people facing a similar problem.
Edit: [user:Schullz,2014-11-16] has given an even better solution: Go to your profile -> "Change settings" -> "Show tag...
settings" -> "Show tags for unsolved problems"
130.
Invitation to ILUPC Replay Contest — 27 August at 8:30 PM (BST) We're excited to invite you to participate in the **[ILUPC Replay Contest](https://serious-oj.com/contests/01a03dab-e17b-75e7-ad2f-abcdf41d9d66)**, hosted on [**SeriousOJ**](https://serious-oj.com/).
The main **ILUPC Team Contest** and **Junior Programming Contest** were held on 19–20 August 2026. For this replay, we have combined the problem sets from both contests into a single contest so that everyone gets another opportunity to participate and enjoy the challenges.
We have mainly focused on the unsolved problems from the original contests, making this a great opportunity to practice, learn, and challenge yourself again.
* **Date:** **Thursday, 27 August 2026 at 20:30 (BST)**
* **Platform:** SeriousOJ
* **Problems:** Combined from ILUPC Team & Junior Programming Contests
* **Problem Setters & Testers:** [user:thakuremon,2025-06-26], [user:mahfuzrahman,2025-06-18], [user:mahmudulsakib2019,2026-08-26], [user:Fahmi_Nafi_46,2026-08-02], [user:sabbirahmedfahim,2026-08-26], [u...
focused on the unsolved problems from the original contests, making this a
great opportunity to practice, :** Mainly unsolved problems from the original contests * **Rating:** Unrated, We have mainly focused on the unsolved problems from the original contests,
making this a great
131.
CF RANDOM UNSOLVED I made a site called [CF Random Unsolved](https://cf-random-unsolved.onrender.com/). It gives you a random Codeforces problem you have not solved yet. You can set the difficulty, pick tags, and you do not need any login. Just type your handle and get a random problem.
**Why I felt the need to create this**
- Picking a problem from problemset took too long and broke my flow
- I wanted new problems every time without repeats without scrolling the problemset
- Filtering by rating or tags felt slow and tedious
- I needed something that works instantly without login even on my phone
**Why it helps**
- No more searching for the next problem
- Every problem shown is new for you
- Easy to focus on a rating range or topic
- No login needed
- Fast to use and good for daily practice
**Updates**
- Added hide rating/problem tags feature
CF RANDOM UNSOLVED, I made a site called [CF Random Unsolved
](https://cf-random-unsolved.onrender.com/). It gives you a
132.
Codeforces Aggregator Hello Codeforces Community!
Have you ever tried to find a common unsolved problem for you and your friends to practice on? Or maybe you wanted to quickly compare your combined problem-solving stats without juggling multiple browser tabs?
It can be a hassle, right? Therefore, hereby I present to you [CF aggregrator](https://cf-aggregator.vercel.app/) !!
CF Aggregator is a simple, fast, and clean web tool that lets you combine data from multiple Codeforces handles into a single, unified dashboard.
What Can It Do?
Multi-Handle Aggregation: Just enter a few handles separated by commas, and the tool will fetch and combine all the data for you. It's perfect for teams or practice groups.
Combined Dashboard: Get a quick overview of your group's collective stats. See the total unique problems solved, the highest max rating in the group, total submissions, and more.
Visual Statistics Tab: A very smart idea to track progress inspired by **cf analytics**
Smart Problem Fin...
Have you ever tried to find a common unsolved problem for you and your friends
to practice on? Or
133.
CodeCoach - a Codeforces recommendation system to identify your highest-ROI topics for practicing So I have been working on a project and I think it's finally ready.
CodeCoach AI is a recommendation system that provides you the topics one might need to practice in order to break away from their current ratings.
https://code-coach-ai-steel.vercel.app/
The working is explained in the ReadMe on github which is accessible from the bottom of the home page. But the basic premise of the project is that instead of going through the route of checking the user submissions to identify the weak topics, I thought that if a person is stagnant on a rating, he ought to be doing what those about 100 to 200 rating points above him have done, since they have broken the barrier the user is stagnant on.
So I first made a pre-compiled collection of users and their submissions, stored in form of rating bands. from 800-900 to 2400-inf. Each rating band has 300 random users of that rating, and for each user, we take the last 500 submissions. Then , lets say if a user is of rating X, we compar...
Then for the top 3 worst topics,we return the top 5 unsolved problem of those
topics in range which
134.
Competitive Machine Learning — AIcrowd Blitz⚡ 
Hello Codeforces!
We at AIcrowd are driven to solve real world problems through challenges and collective effort of the data science community.From experts to enthusiasts we appreciate and value the participation and contribution of each and every single member of the community.
We realised, that at the heart of solving these varied, complex , open-ended and sometimes 'yet-unsolved' real world challenges, lies the crucial art of problem solving, an art which is very much what this brilliant community of CodeForces is all about!
So we welcome you all to participate in our **[AIcorwd Blitz](https://www.aicrowd.com/challenges/aicrowd-blitz-may-2020?utm_source=codeforces&utm_medium=post&utm_campaign=AIcrowd-Bitz)**, a 15 day competition for all AI/Ml enthusiast, with a touch of competitive programming especially for you guys.
Let us join these two different and yet similar communities and do what we all...
-unsolved' real world challenges, lies the crucial art of problem solving, an
art which is very much
135.
ProblemsHunter- Find unsolved problems of a set of users of given rating ProblemsHunter
==============
Hey everyone,
I have made this bot that searches problems on codeforces that are unsolved by a set of users and of given
problem ratings.
Motivation
------------------
To create mashup for virtual participation in group we need problems that are of given rating and unsolved by all who are participating in the contest and this bot automates the cumbersome part of finding problems.
### [Link to bot](https://github.com/YashKumar2001/ProblemsHunter)
Screenshots:
### UPD1:
Realising the fact that mashup problem submissions doesnot show up in user submissions I have tweaked the bot to avoid returning any problems that the bot returned in past.
### UPD2:
Added the feature to add participants directly from the mashup invitation link.
ProblemsHunter- Find unsolved problems of a set of users of given rating, codeforces that are unsolved by a set of users and of given problem ratings.
Motivation
136.
Competitive Machine Learning — AIcrowd Blitz⚡ #2 
Hello Codeforces!
We at AIcrowd are driven to solve real world problems through challenges and collective effort of the data science community.From experts to enthusiasts we appreciate and value the participation and contribution of each and every single member of the community.
We realised, that at the heart of solving these varied, complex , open-ended and sometimes 'yet-unsolved' real world challenges, lies the crucial art of problem solving, an art which is very much what this brilliant community of CodeForces is all about!
So we welcome you all to participate in our **[AIcorwd Blitz #2](https://www.aicrowd.com/challenges/aicrowd-blitz-2?utm_source=codeforces&utm_medium=forum&utm_campaign=AIcrowd%20Blitz%20%232)**, a 15 day competition for all AI/Ml enthusiast, with a touch of competitive programming especially for you guys. This time in the challenges you will dance with skeletons, play chess and b...
-unsolved' real world challenges, lies the crucial art of problem solving, an
art which is very much
137.
Google Onsite Interview question — Unsolved This question is originally posted on [LeetCode](https://leetcode.com/discuss/interview-question/799477/google-phone-screen-reject) by several anonymous users but it doesn't have any good answer there.
You are implementing a board game where you are given a size N x M for the board, where N is the number of rows and M is the number of columns.
In this board game, you are playing with some fixed size lego pieces, where each player places 1 piece on the board every turn until no more piece can fit onto the board, and the last player to move wins.
The problem is to implement a method for making a move on this board, placing a piece wherever there is space available and returns a boolean indicating whether or not the player that has just made the move has won.
Follow up question: The method should also find if there is any move that can be made that will make it so that the next player is unable to place a piece anywhere on the board in their next turn, and make that move.
Yo...
Google Onsite Interview question — Unsolved
138.
CF Upsolver — Kenkoooo for Codeforces. No AI BS I took inspiration from Kenkoooo’s AtCoder Problems and thought, **why doesn’t Codeforces have something this clean?**
So I built it.
Try it: https://sodawater789.github.io/SideQuest/
Source: https://github.com/SodaWater789/SideQuest
**No AI BS. Just the problems you actually want to solve.**
No LLM-generated "smart recommendations," no black box deciding what's good for you.
It's one static HTML file that calls the public Codeforces API and filters the results with plain JavaScript.
## **What it does**
1. Pulls contests, problems, and your accepted submissions for any handle.
2. Filters by tag, rating range, contest category (Div. 1/2/3/4, Educational, Global...), and problem letter — want to grind only Bs today? One click and every contest collapses to just its B.
3. Hides contests you've effectively cleared within your current filter, so solving A and B doesn't mean staring at an unsolved F for eternity.
4. Stars unsolved problems into a personal upsolve q...
doesn't mean staring at an unsolved F for eternity. 4. Stars unsolved problems
into a personal upsolve, effectively cleared within your current filter, so solving A and B doesn't
mean staring at anunsolved F
139.
Topic Wise Problem Separation Whenever I learn a new algorithm or data structure, I always spend a lot of time finding problems related to that specific topic from previous contests on Codeforces or some good Competitive Programming Website. Many people told me to use Codeforces tags. Still, I feel that they are too many problems that will blow up your mind, or you might end up solving a similar type of problem-based on a topic(algorithm or data structure) which means you are not learning anything new and is counterproductive.
After a year of extensive search, I have found out 5 good resources which solve this problem.
[cut]
---------------
1) Competitive Programming 4: This is a book with 2 parts, which has good handpicked problems from UVa OJ, Kattis, previous year ICPCs and IOIs problems. As of today, this book doesn't have a soft copy, but the author says that they will make it available sometime in the second half of 2021. But still, the Hard Copy of this book has reasonable pricing, and the value of t...
website mostly for its feature to accumulate unsolved problems from the
contests we have attempted
140.
CPH2H 1v1 Codeforces Tournament [no rating limit??] As we are drawing closer to the competition date, I found it fitting to push out another announcement!
**I AM REMOVING THE 1900 ELO REQ**
If you wanna participate in something like CF Blitz Cup, sign up!
On August 23, CPH2H is running a remote, single-elimination 1v1 Codeforces tournament.
Both players receive the same problem. The first accepted solution wins.
Cameras and microphones stay on. Matches last up to 40 minutes. Unsolved matches move to sudden death.
Registration is open to all Codeforces users. The 64 highest-rated applicants will enter the bracket. Selection is based on Codeforces rating when registration closes.
This is direct competition under pressure, not another anonymous scoreboard.
**Date:** August 23, 2026
**Time:** 2:35 PM UTC
**Prize pool:** $500, sponsored by FR8
Register: https://cph2h.com/tournament
Cameras and microphones stay on. Matches last up to 40 minutes. Unsolved
matches move to sudden
141.
Chrome Extension to show only difficulty tag on the problem page Hi all,
As far as I remember a couple of months ago I saw a post (or comment) on Codeforces with the link for the extension that allows showing only difficulty tag for the unsolved problems on the particular problem page (like https://codeforces.me/problemset/problem/1385/G).
Could anyone suggest a link to the post, the comment, or the extension? I have tried to Google it but did not manage to find.
for the extension that allows showing only difficulty tag for the unsolved
problems on the particular, the link for the extension that allows showing only difficulty tag for the
unsolved problems on the
142.
creating arbitrary rational chances from flipping coins Hello codeforces! A while back I presented myself with a challenge to build a random function from only random bits. However, in the process of doing so, I realized that not only was this much more difficult than I expected, I ended up wondering whether it is possible at all. So here's what I did and the challenges I faced before asking you for a solution:
Creating 1/powers of 2 is trivial, since flipping n coins can create 2^n random possibilities.
Similarly, the same thing would be possible with dice, for example flipping two die and then multiplying one dice by 6 and adding them together can yield a 1/36 chance.
This seems to be limited to the factors given though, a dice can create 1/12 or 1/18 as well, using mod.
I don't want to have to flip potentially infinite coins. So, I can't get a 1/8 chance and then reroll on an 8 to get a 1/7 chance.
I first attempted to use different flips of powers of two using the binary representation. For example, for a 1/7 chance I tho...
Apologies if this is a solved problem, or if this is a well known unsolved
problem. This was on my
143.
101 Hack March on HackerRank Hello everyone!
I invite all of you to take part in the contest [101 Hack March](https://www.hackerrank.com/101mar14). The link for the contest [start time](http://www.timeanddate.com/worldclock/fixedtime.html?month=3&day=29&year=2014&hour=22&min=0&sec=0&p1=553) in different timezones. There will be five problems in two hours. I am the author of the problems and in my opinion problems are very interesting.
Attentive people can observe, that in 30 minutes before this contest the TopCoder SRM 614 will start. I want you to participate at HackerRank and would like to mention, that top-10 contestants will receive t-shirts! It is your choice where to participate, however, there are four SRM-s per month at TopCoder, but at HackerRank you will have a chance to win exclusive t-shirt!
Again, in my opinion, problems for the contest are very good, and it wouldn't be nice if these problems will stay unsolved :)
Many thanks to all of you, who will take part in 101 Hack March!
problems will stay unsolved :)
144.
No more spoilers in editorials 
If you read editorial after solving one of the archived problems and don't want to spoil unsolved ones, you might find this [custom javascript extension](https://chrome.google.com/webstore/detail/custom-javascript-for-web/poakhlngfciodnhlhhgnaaelnpjljija) snippet useful:
```js
$(function() {
if ($("a.tag:contains('editorial'),a.tag:contains('tutorial')").length === 0) return;
$(".content h2, .content h3").each(function(a,b) {
var $h = $(b);
var $t = $h.nextUntil('h2, h3');
$h.after("<a href='#' class='show-spoiler'>show</a>");
var $l = $h.next('.show-spoiler');
$l.click(function() {
$t.css('visibility', 'visible');
$l.remove();
return false;
});
$t.css('visibility', 'hidden');
});
})
```
I have not tested it on each and every editorial ^_^
upd1: fixed issue with picking 'editorial' links from new's block
If you read editorial after solving one of the archived problems and don't want
to spoilunsolved
145.
An unsolved problem from an Korean ICPC contest Last week, there was a preliminary ICPC contest in Korea, whose result is used to select teams from various universities to advance to the Seoul Regional (regional contest in Korea)
This is the problemset: [http://icpckorea.org/2018/preliminary/problems.pdf](http://icpckorea.org/2018/preliminary/problems.pdf)
Most problems were solved, at least algorithmically, by people during the contest or after the contest. However, anyone, including some top-tier people in our country, couldn't solve **problem C**.
In the contest, problem C was solved, but it was just because the test data was super weak to allow solutions with complexity $O(n^2 / k)$ :p Since the description is short enough, I will not describe the problem here, just click the link to see the task.
I am really curious about the solution of this problem. Could I get some hints or entire solutions for this task? Thanks in advance :)
An unsolved problem from an Korean ICPC contest
146.
Unsolved Problems Why my codeforces account doesnot show my unsolved problems ? instead of that it shows last submissions and i think it was better to see unsolved tasks.
Unsolved Problems, Why my codeforces account doesnot show my unsolved problems ? instead of that
it shows last
147.
API is Broken Hi Codeforces team and [user:MikeMirzayanov,2026-05-03],
I know maintaining Codeforces is a huge amount of work, especially with the number of submissions and API requests every day, so thanks for all the effort.
I wanted to ask about a small issue with the API. I use it to hide problem tags while solving, so I can try problems completely on my own. Recently, without the API working properly, I can’t reveal the tags with View tags, and I also can’t see the problem rating unless I enable `Show tags for unsolved problems` on the Problemset page.
Also, could Codeforces maybe support this natively? Ideally, there would be an option to show only the problem rating by default, while keeping the tags hidden behind a button like `View tags`.
I think this would be useful for people who want to choose problems by rating but avoid spoilers from tags.
Thanks again for everything you do for the platform.
unsolved problems` on the Problemset page.
148.
Website to make you never miss upsolving problems. Ever happened that you gave a contest so bad that you didn't even want to upsolve problems and you just leave the contest and decide to retire in peace?
For me, it happens a lot, and those questions never get upsolved. That's why I created this website which gives me a list of problems that I haven't upsolved and ta-da now I can revisit those problems and learn from them.
How am I filtering these problems?
1. Fetch all the official contests you participated in last 6 months (who even cares before that).
2. In those contests, find all unsolved problems whose rating lies <= (peak rating + 200).
3. Skip problems whose rating isn't defined as of now.
WEBSITE : https://go-upsolving.vercel.app/
Note: It might take 5-10s to load since Codeforces has a rate limiter which doesn't allow too many API calls at once.
Suggestions are welcome!
2. In those contests, find all unsolved problems whose rating lies <= (peak
rating + 200).
149.
Hidden Solutions in Gyms Hello!
Last week, I participated virtually in a Gym with a team. After the contest, we wouldn't have been able to open the solution of a problem that wasn't solved with us if the team hadn't had a previous Div.1 contestant in it (using Coach mode).
So, I wondered, what is the preference of the Div.1 contestants on others in this point?
If the answer is _because they may need the solutions for coaching purpose_, so why don't we consider the self-coaching case that is not a rare case?
1. We all know that during practice, one, anyone, needs to see the solutions of the unsolved problems after trying hard with it.
2. Becoming a Div.1 contestant can be done by cheater non-Div.1 contestants (and I really appreciate your efforts to defeat a lot of cheating cases).
So, I ask you, please, to discuss this point, and I wish the solutions of the author who accepts to share his solutions to be opened for all.
Thanks!
1. We all know that during practice, one, anyone, needs to see the solutions of
theunsolved
150.
How to solve this array based problem ? | Unsolved since 5 years | Try it Given 2-arrays "$A$" and "$B$" of length $n$ , calculate maximum possible product of all elements of array "$C$" ,
where,
$C[i] = A[j]*B[k] $
Or
$C[i] = A[j] + B[k] $,
(its your choice, what to select from both of them)
for all $1<=i<=N$
Once an index 'j' and 'k' have been used from array A and B respectively, you can't use them ever again.
Find the maximum possible value of C[1]*C[2]*......C[N] modulo p , where p = 1000000007.
$1<=A[i]<=100000 $
$1<=B[i]<=100000 $
$1<=N<=100000 $
Example :
Array A : [1,2]
Array B : [4,3]
Best possible array C :$ [(3+1),(4*2)] = [4,8] .$
Final answer = 4*8 = 32 which is the maximum possible product.
I applied the greedy approach in the test which failed all the test cases except 1.
My greedy approach was : Sort both "A" and "B", then do $C[i]=max(A[i]+B[i], A[i]*B[i]) $
Second problem of the test was : Given a graph with $N$ nodes and $M$ edges , remove any number of nodes you want to ...
How to solve this array based problem ? | Unsolved since 5 years | Try it
151.
How to find the kth maximum slope in this problem. Still unsolved. please tell. Maroof is visiting a new city. Being a Mathematician, he does not like to visit different places but visit places differently. The city has N places to visit. We are given the (X,Y) co-ordinates of the places to visit. Maroof wants to start from a random place i and want to go to a random place j. But he involved a little maths in his procedure. Following are his demands:
He will give a number A. Now, the place i and place j should be such that the line connecting these two points must have the Ath maximum slope (There are total N*(N-1)/2 possible slopes among all the unordered places pairs).
Input arguments to your function:
1. Integer A
2. B : An integer array containing X-coordinates of the places
3. C : An integer array containing Y-coordinates of the places
Note that the length of B (= N) will be equal to the length of C and the ith point is represented by `(B[i], C[i])`.
Output: An array having exactly 2 elements : numerator and denominator of the slope (fra...
How to find the kth maximum slope in this problem. Still unsolved. please tell.
152.
CfLockout — Practice Codeforces Problems with Friends in a Competitive Way Hi Codeforces,
I have tried making a web app — **CfLockout** that allows you to create practice contests of Codeforces problems. You can select different ratings of the problems and only the problems which are unsolved by all the participants appear in the contest.
Only the user who solves the problems first is awarded the score, so be quick to solve the problems ;)
Website link — https://cflockout.vercel.app
Github link — https://github.com/prayutsu/cflockout
Note — Email verification mails may lend in your spam folder, mark them **not phishing** to be able to click the verification links.
Do star the repository if you like the project.
Update #1: The maximum number of problems allowed has been increased to **10** and the maximum difficulty of the problems is now **3500**.
are unsolved by all the participants appear in the contest.
153.
List of unsolved/unattempted problems? It's tragic that i no longer have access to my old account.
I want to try the unsolved problems from old account, and may be don't want to see again the solved ones.
Is there any way to find out the list of unsolved/unattempted problems (taking both codeforces_accounts into account).
I mean mark it solved, if it has been solved by atleast one account.
Thank you in advance.
List of unsolved/unattempted problems?, I want to try the unsolved problems from old account, and may be don't want to
see again the solved, Is there any way to find out the list of unsolved/unattempted problems (taking
both, It's tragic that i no longer have access to my old account. I want to try the
unsolved problems
154.
Problemset Unsolved Filter Hi Codeforces members / admins.
It should be great that there is an unsolved questions filter at problemset pages. What do you think?
Problemset Unsolved Filter, Hi Codeforces members / admins. It should be great that there is an unsolved
questions filter at
155.
Custom Mashup Creator Hello community,
I am sharing a [custom mashup creator](https://code-sync-sandy.vercel.app/) which can create a contest-like environment with questions fetched based on the Codeforces handles provided. It works in both individual and team modes.
This addresses the specific issue that when we choose any normal Codeforces round (say a Div 2) for a virtual contest, the first few questions are quite easy and the last few are almost undoable for a majority of the people, so the area where you can test yourself becomes small. But here you can choose the difficulty range to fetch only those questions that have not been attempted by you even once.
It may also prove beneficial to those preparing for team contests like ICPC as it allows you to create contests with common unsolved problems for the team, with the option for shuffling.
More features like past contests, teams, etc. for signed-in users.
Open to suggestions and bug reports.
Thank you
create contests with common unsolved problems for the team, with the option
for shuffling.
156.
Something wrong with "Last Unsolved" Well, I found there're some problems with the "last unsolved". It will display the problem I solved.
For example I just solved problem 1A [submission:37353205] but on my last unsolved, it is still there. And some of my friends reported this bug too. Is it a new feature or just a bug,or it's just a problem of our explorer? [user:MikeMirzayanov,2018-04-15]
Something wrong with "Last Unsolved", For example I just solved problem 1A [submission:37353205] but on my last
unsolved, it is still, Well, I found there're some problems with the "last unsolved". It will display
the problem I solved
157.
Request for a feature to show difficulty rating and not tags I would love it if we could hide the problem tags, but at the same time be able to see difficulty inside the problem statement. Sometimes I get a link to a random question (through some resource) and I have to go to the problemset to check "show tags for unsolved problems", so that I can see the rating of the problem.
It'd be nice to have a separate option to enable difficulty rating. What do you guys think?
I have to go to the problemset to check "show tags for unsolved problems", so
that I can see the
158.
Баг Codeforces? Today in the evening I have been solving problems from problemset. When I have opened new problem, I got an error<div><b>RPC call for action failed</b>:</div><div><img src="http://habrastorage.org/storage/a048b566/181e66fa/1651079d/a168da04.png"><div><br></div><div>I caught this error in unsolved problems only, but solved problems can be opened without any errors.</div></div><div>Who knows, what has happened?</div><div><br></div><div>P.S. Sorry for my bad english :)</div>
I caught this error in unsolved problems only, but solved problems can be
opened without any
159.
Solving in gym bug? I've noticed this issue a lot. When I solve some problems in a gym contest (without coach mode), open the coach mode and then view any submission in the contest, all my solutions disappear from standings, status and from my submissions. And I have to open the coach mode to find them in the standings. Also the problems are marked as unsolved (They are not green anymore) and this particularly is really annoying.
Did anybody notice this issue before? And is it a bug or this is intended to happen? I hope it's a bug :D
standings. Also the problems are marked as unsolved (They are not green
anymore) and this particularly is
160.
Invitation to ProCon'16 Hi Codeforces,
We at IIIT-Delhi would like to invite you to ProCon 2016, the annual programming contest conducted as a part of our technical festival. We will have 6-7 problems of varying difficulty over 2.5-3 hours with ACM style scoring.
Also, there are prizes worth 20k INR for top Indian students.
**Contest starts August 6, 2016, 21:00 IST**<br>
Check in your timezone [here](http://www.timeanddate.com/worldclock/fixedtime.html?msg=ProCon%2716&iso=20160806T21&p1=176&ah=2&am=30)<br>
Register at: [http://esya.iiitd.edu.in/events/procon/register](http://esya.iiitd.edu.in/events/procon/register)(for prizes)<br>
Link to contest: https://www.codechef.com/PROC2016 <br>
RSVP: [Facebook event](https://www.facebook.com/events/266411510390281/)<br>
**EDIT**: contest starts in less than 24 hours.<br>
**EDIT**: contest starts in 3 hours. We have 6 problems, and 2.5 hours for you to solve them. Good luck!<br>
**EDIT**...
problems remain unsolved.
**EDIT**: Winners will be listed here after a plag check, and
161.
AtCoder Analytics — a Chrome extension for AtCoder profiles Hi everyone,
I just published AtCoder Analytics, a Chrome extension that adds extra stats to AtCoder user profile pages.
I started this because I noticed another AtCoder-related extension I used stopped working (likely due to site/API changes), so I decided to build a lightweight alternative and publish it.
Features
- Solved-by-difficulty histogram (estimated difficulty)
- Solved breakdown by contest series (ABC/ARC/AGC/AHC/etc.)
- Unsolved list (with links)
Chrome Web Store link: https://chromewebstore.google.com/detail/bmfjngielhkffoekjpdgpedpmelhabhm?utm_source=item-share-cb
Feedback and bug reports are welcome.
/ARC/AGC/AHC/etc.) - Unsolved list (with links)
162.
Issue Related Last Unsolved Problems Hello Codeforces,
I have some issue related to last unsolved problems. I solved some problems but still, I can see in my unsolved problems section.
Please help me to get rid out of this my problem.
<img src="https://www.imageupload.co.uk/images/2018/04/14/My.png" border="0">
Thank you in advance.
[cut]
Issue Related Last Unsolved Problems, Hello Codeforces, I have some issue related to last unsolved problems. I solved
163.
Pupil in 80 days - Day 3 ### Hello Codeforces!
Today I hardly solved problems, but devoted time to theory. I solved several problems on the topic Binary Search and 2 pointers from other sites, looked for materials on the topic Dp, and today I almost finished the 1st topic from the ITMO Academy course.
It’s strange, because today, without practicing, I wrote a better contest than yesterday.
#### Plans for tomorrow:
Complete the remaining unsolved problems, end the 1st topic of the course, and write a contest from the coach.
### Till tomorrow!
Complete the remaining unsolved problems, end the 1st topic of the course, and
write a contest from
164.
Pupil in 80 days — Day 10 ### Hello Codeforces!
Today is the 10th day since the beginning of my journey (1/8 part). Today I practiced problems from other sites on the topic of mathematics, number theory and recursion. Also today I solved the first ten problems from Project Euler, and completed the 3rd topic of the CF course. And also, today I have a lot of questions regarding competitive programming, here are some of them:
#### Will CodeForces help improve your overall skill in competitive programming, or will it help only on the CF platform?
#### What specific sports programming topics are needed to reach the pupil?
Today I also had a lot of time, but I didn’t have enough patience to finish the 2nd topic of the Informatics website. Now we have to put it off until tomorrow >:(
#### Plans for tomorrow:
Finish this unsolved topic, get together and finish the last 2 contests, solve more problems and also DON’T LOSE MOTIVATION!
### Till tomorrow!
Finish this unsolved topic, get together and finish the last 2 contests, solve
more problems and
165.
Old submissions disappeared before June 8 Handle: Het2007
Today I noticed that all my submissions before June 8, 2026 disappeared.
Symptoms:
* Solved problem count dropped significantly.
* Submission history only goes back to June 8.
* user.status API also does not return submissions before June 8.
* Problems solved before June 8 now appear unsolved.
I did not change my handle or account settings.
Has anyone experienced something similar, or can a Codeforces administrator please investigate?
Thank you.
appear unsolved.
166.
The lesser of two evils I’ve set myself the goal of achieving 1900 over the year. One of the steps towards this goal is solving problems from the book "Selected Problems and Theorems of Elementary Mathematics". My plan is to solve the entire book over the year, doing 5 problems per day (consecutive ones, of course). The first couple of days went well, but as you know, olympiad math problems can really block you if you can't come up with a specific idea.
Now I’m wondering, what would be the better approach: should I stick to this pace and, if I don’t manage to solve all 5 problems in a day, read the solutions to the unsolved ones and move on, or should I give myself a conditional 3-day limit per problem (and not solve others during that time), after which I can check the solution? In other words, which approach will lead to stronger progress? Will I make more progress by rushing through the whole book and solving about half of the problems myself, or will I benefit more if I get stuck in some areas, solving...
manage to solve all 5 problems in a day, read the solutions to the unsolved
ones and move on, or
167.
Solved problem appearing in latest unsolved. Problems that I fail to AC in 1st time get stuck in my latest unsolved list even though I do get an AC, it's getting really annoying.
Anyone else experiencing the same issue ?
[user:MikeMirzayanov,2018-04-20]
Solved problem appearing in latest unsolved., Problems that I fail to AC in 1st time get stuck in my latest unsolved list
even though I do get an
168.
Problems solved in mashups Codeforces allows us to create mashups, and run it as a contest. I noticed a problem in it. If you solve and get AC on any problem in a mashup contest, it won't be reflected in the problem page in the contest from which it was taken. For example, if you solve Problem A from Round 410 in a mashup, and then go to the Round 410's problem A page, it will be shown as unsolved.
Is this a bug? Or was it intended to be like this? (which doesn't make much sense). Or do I have to wait for a certain amount of time for the change to take place?
If this is a bug, please correct this codeforces! Thanks!
, and then go to the Round 410's problem A page, it will be shown as unsolved.
169.
Feature Request: Contests history filter I think, it would be helpful to have a filter on the contests history page. For example, filter by division, by a taking part and by duration. Like it has been implemented for the gyms page. It may help to find unsolved div. 2 only contests or special rounds.
Picture to attract your attention.
**UPD0** Maybe add order of sorting.
help to find unsolved div. 2 only contests or special rounds.
170.
Can't hide unsolved problems' tag Hello there!
I have been trying to hide tags for unsolved problems or contact information
but the settings return as they were automatically _after some hours or days_,
hope CF's staff to solve it, thanks!
[user:MikeMirzayanov,2018-04-01]
Can't hide unsolved problems' tag, Hello there! I have been trying to hide tags for unsolved problems or contact
information but, I have been trying to hide tags for unsolved problems or contact information
but the settings
171.
Old submissions disappeared before June 8 Handle: Het2007
Today I noticed that all my submissions before June 8, 2026 disappeared.
Symptoms:
* Solved problem count dropped significantly.
* Submission history only goes back to June 8.
* user.status API also does not return submissions before June 8.
* Problems solved before June 8 now appear unsolved.
I did not change my handle or account settings.
Has anyone experienced something similar, or can a Codeforces administrator please investigate?
Thank you.
appear unsolved.
172.
Upsolve Codeforces As we all know upsolving is very important to improve your level because it forces you to solve harder problems which you couldn't solve during contest. I wrote a python [code](https://github.com/dush1729/Upsolve-Codeforces) which uses codeforces API to find all the unsolved problems. You can find more description in the link. I know it's a bit slow(takes 4-6 seconds to parse one participated contest). That's why it saves the list in a file at the end. Please give it a try. :)
Known issue — This fetches almost all problems. Not all because [http://codeforces.me/api/problemset.problems](http://codeforces.me/api/problemset.problems) doesn't return all contest problems as expected. :( Need to find a fix for this.. Do send a pull request to github repo if you find it first. ;)
/dush1729/Upsolve-Codeforces) which uses codeforces API to find all the unsolved
problems. You can find
173.
Practice previous contest problems Hi folks, recently I have created a small web application where we can find the link of the specific problems from recent past contests. You can add filters according to the contest type and problem number along with the user id and categories it into solved, unsolved and hold problems, once you first fetch the data, it will be stored locally. Username, contest type, and problem number should be filled for the application to load the problems.
I am still working on this so there might me some scope for improvement.
Hope you will like it.
GitHub Repo: https://github.com/sanjay-1458/Codeforces-Recent-Problem-List
Edit:
The live link fetch only 5 problems for now, and you can set the number of problems in the JavaScript file. The time taking for the problems to display on the UI depends upon the number of problems and currently it takes almost 2 minutes for 10 problems.
The current issue which you may face is you have to set the number of problems from JavaScript file and the wa...
number along with the user id and categories it into solved, unsolved and hold
problems, once you
174.
Help solving this query problem[Still unsolved] Hi Coders,
I am trying to solve a problem but couldn't come up with a better solution.
**Problem Statement**
Given an array $A$ of $N$ integers and $Q$ queries where $1 \le A_i \le 100$, $1 \le N \le 10^5$ & $1 \le Q \le 10^5$. Each query gives $L$ and $R$(a subarray of array $A$). For each query find the minimum $X$ such that $A_X > A_{L+X-1}$ and $L+X-1 \le R$.
I tried solving this problem but couldn't come up with a solution better than $Q \times N$. Any help to improve the complexity would be much appreciated.
Help solving this query problem[Still unsolved]
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