brackets instead of round), where n is an integer starting from 1, to allow
for voting., ) (use square brackets instead of round), where n is an integer starting from
1, to allow for
→ Pay attention
→ Top rated
| # | User | Rating |
|---|---|---|
| 1 | Benq | 3676 |
| 2 | Kevin114514 | 3657 |
| 3 | jiangly | 3638 |
| 4 | turmax | 3442 |
| 5 | tourist | 3380 |
| 6 | Um_nik | 3353 |
| 7 | strapple | 3350 |
| 8 | squareOf105 | 3346 |
| 9 | heuristica | 3322 |
| 10 | maroonrk | 3310 |
→ Top contributors
| # | User | Contrib. |
|---|---|---|
| 1 | Qingyu | 158 |
| 2 | nik_exists | 151 |
| 3 | maspy | 150 |
| 4 | AmShZ | 144 |
| 4 | Um_nik | 144 |
| 6 | Errichto | 139 |
| 7 | adamant | 137 |
| 8 | BledDest | 135 |
| 9 | maroonrk | 133 |
| 10 | Proof_by_QED | 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.
round
Last visit:
11 years ago
Registered:
14 years ago
2.
Congratulations: Tourist has reached a rating of 4000! Hello,
As you may have already noticed, [user:tourist,2024-08-31] has reached the symbolic milestone of 4000 rating points. This is the first time in the history of competitive programming. I, personally, and the entire Codeforces team, congratulate Gennady [user:tourist,2024-08-31] Korotkevich on this incredible achievement!
Right now, we have assigned a new rank “Tourist” to the 4+ rating. This highlights the uniqueness of the moment!
However, in the future, I would like to change this name to something a bit more neutral (or leave it Tourist?). Would you help me with this?
I’d appreciate your cool suggestions in the comments!
Here are a few options from me. Please, vote:
- Epic Grandmaster
- Ultimate Grandmaster
- Godlike Grandmaster
- Tourist
- 4K Grandmaster
- Grandmaster 4K
- Legendary Grandmaster 4K
- Joke option: Ultra HD Grandmaster
- from [user:Tlatoani,2024-08-30]: Champ...
3.
Codeforces Global Round 5 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width:200px; float:right; margin: 0 1em 1em 1em"/>
Hey!
On [contest_time:1237] we will host [contest:1237].
It is the fifth round of a new series of [Codeforces Global Rounds](https://codeforces.me/blog/entry/65002) supported by XTX Markets. The rounds are open for everybody, the rating will be updated for everybody.
The round will last for 2 hours 30 minutes, 8 problems are waiting for you, and one of them will be proposed in two versions.
Scoring distribution: **500 — 750 — (750 + 750) — 2000 — 2500 — 3000 — 3750 — 4000**
The prizes for this round:
- 30 best participants get a t-shirt.
- 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.
The prizes for the 6-round series in 2019:
- In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT).
- The fi...
Codeforces Global Round 5, **UPD:** The round is over!
[Editorial](https://codeforces.me/blog/entry/70620) is here, - In each round top-100 participants get points according to the
[table](https://pastebin.com, Coincidentally, this is also the list of people I'm thankful to for making this
round what it is., It is the fifth round of a new series of [Codeforces Global
Rounds](https://codeforces.me/blog, The prizes for the 6-round series in 2019:, The prizes for this round:, The problems of this round were developed by me, and here is the list of people
who can't take part, The round will be perfectly balanced. As all things should be., The round will last for 2 hours 30 minutes, 8 problems are waiting for you, and
one of them will be
Announcement of Codeforces Global Round 5
4.
Codeforces Round #752 #### UPD: (28 April, 2022)
<spoiler summary="Donated Finally">
Details: [here](https://codeforces.me/blog/entry/96333?#comment-907470)
</spoiler>
আবার চলে এসেছি! (That's Bengali for "I am back! (in Terminator mode)")
I am super excited to invite you to participate in [contest:1603] and [contest:1604] which will be held on [contest_time:1604]. This round is rated for both divisions.
You will be given $6$ problems in each division and $2$ hours to solve them. All the problems are authored and prepared by me.
I would like to thank -
- [user:antontrygubO_o,2021-10-26] for his breathtaking(<strike>literally</strike>) coordination of the round. <i style="color:White;"> no funny text this time</i>
- [user:Alpha_Q,2021-10-26], [user:Anachor,2021-10-26] and [user:antontrygubO_o,2021-10-26] for putting up with my dumb ranting and helping with the problems.
- [user:Um_nik,2021-10-26], [user:gamegame,2021-10-26], [user:kefaa2,2021-10-26], [user:dorijanlendvaj,2021-10-26], [u...
Codeforces Round #752, [contest:1604] which will be held on [contest_time:1604]. This round is rated
for both divisions, held on [contest_time:1604]. This round is rated for both divisions., the round. no funny text this time - [user:Alpha_Q,2021-10-26
Announcement of Codeforces Round 752 (Div. 1)
Announcement of Codeforces Round 752 (Div. 2)
5.
Codeforces Round #712 omg hi!
I am pleased to invite you to participate in [contest:1503] and [contest:1504]! You will be given **6 problems** and **2 hours 15 minutes** to solve them. I'm happy to announce the theme of this round is déjà vu!
I would like to thank the following people:
- <a class="rated-user user-red" href="https://images.emojiterra.com/twitter/512px/1f921.png" title="The Entire Circus">antontrygubO_o</a> for accepting all of my problems <span style="color:white;">at gunpoint</span>
- <a class="rated-user user-orange" href="/profile/Nika_Tamliani" title="Useless Tester Nika_Tamliani">Nika_Tamliani</a>, <a class="rated-user user-violet" href="/profile/arvindr9" title="Useless Tester arvindr9">arvindr9</a>, <a class="rated-user user-red" href="/profile/dorijanlendvaj" title="Useful Tester dorijanlendvaj">dorijanlendvaj</a>, <a class="rated-user user-blue" href="/profile/I_Love_YrNameCouldBeHere" title="Useful Tester I_Love_YrNameCouldBeHere">I_Love_YrNameCouldBeHere</a>, <a class="r...
Codeforces Round #712, -orange" href="/profile/kpw29" title="Useful Tester kpw29">kpw29 for testing the
round and being, round is déjà vu!
Announcement of Codeforces Round 712 (Div. 1)
Announcement of Codeforces Round 712 (Div. 2)
6.
About div1E (round #810) I am the coordinator of Round #810. I will be brief and clear.
The div1E problem was copied by one of the two authors, it was not a coincidence.
For this reason, the **div1 part of the round is unrated**. Div2 stays rated.
Sometimes known problems appear in a contest, it happened to me as an author and to any problem setter who has organized many contests. This is never a reason to make a round unrated.
Today something different happened, the problem was deliberately copied and the author did not tell anything to anybody (not even to the other author). Codeforces (and me personally) condemns this behavior.
A final personal remark: I feel sad. Please future authors: do not copy problems. It's a waste of everyone's time.
About div1E (round #810), setter who has organized many contests. This is never a reason to make a round
unrated. Today, For this reason, the **div1 part of the round is unrated**. Div2 stays rated., I am the coordinator of Round #810. I will be brief and clear.
Announcement of Codeforces Round 810 (Div. 1)
7.
About the Failed Round 591/Technocup 2020 — Elimination Round 1 Hi Codeforces!
Unfortunately, ill-wishers thwarted the round by making DDOS on our infrastructure. Neither the coordinator nor the writers of the round are subjects to blame for the failure. Please do not downvote the announcement of the round. I think that this situation is an additional reason to support the writers. They worked hard and prepared good problems!
Apparently, such an attack should be regarded as a symptom of the fact that Codeforces outgrew the youth phase and entered serious adult life. Of course, we will respond with adequate measures to protect ourselves from such incidents. Fortunately, for almost 10 years of work, a large community has formed around those who care about Codeforces. We are not worried about possible additional expenses or efforts. We can do this. The rounds must go on.
— [user:MikeMirzayanov,2019-10-06]
**UPD 1:** All three of today's rounds will be unrated.
**UPD 2:** Hooray! Today we've survived another DDOS attack. The round ...
About the Failed Round 591/Technocup 2020 — Elimination Round 1, **UPD 2:** Hooray! Today we've survived another DDOS attack. The round was not
perfect, but it was, Hi Codeforces! Unfortunately, ill-wishers thwarted the round by making DDOS on
our, Unfortunately, ill-wishers thwarted the round by making DDOS on our
infrastructure. Neither the
8.
Codeforces Round #733 (Div. 1 + Div. 2) Hello, Codeforces!
Welcome to the [contest:1530] that will start on [contest_time:1530]. It will be a combined rated round for both divisions.
This round is a mirror of VK Cup 2021 Elimination. VK Cup is an annual championship for Russian-speaking competitors organized by VK — a social networking service based in Saint Petersburg and the most popular website in Russia. VK Cup [started in 2012](https://codeforces.me/vkcup2012) and has grown to be a four-track competition in competitive programming, ML, design, and mobile development.
All the problems were authored and prepared by me. Big thanks to everyone without whom this round would not be possible: [user:PavelKunyavskiy,2021-07-16], [user:KAN,2021-07-16], [user:lperovskaya,2021-07-16], [user:ksun48,2021-07-16], [user:Sert,2021-07-16], [user:Aleks5d,2021-07-16], [user:MikeMirzayanov,2021-07-16].
You will be given 8 problems and 3 hours to solve them. It is recommended to read all the problems. Good luck!
**UPD*...
Codeforces Round #733 (Div. 1 + Div. 2), -17] 4. [user:Golovanov399,2021-07-17] 5. [user:kefaa2,2021-07-17] Codeforces
Round #733: 1, All the problems were authored and prepared by me. Big thanks to everyone
without whom thisround, Codeforces Round #733:, This round is a mirror of VK Cup 2021 Elimination. VK Cup is an annual
championship for Russian, round for both divisions.
Announcement of VK Cup 2021 - Elimination (Engine)
9.
Codeforces Global Round 9 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width:200px; float:right; margin: 0 1em 1em 1em"/>
Hi!
On [contest_time:1375] we will host [contest:1375].
It is the third round of a 2020 series of [Codeforces Global Rounds](/blog/entry/65002). The rounds are open and rated for everybody.
The prizes for this round:
- 30 best participants get a t-shirt.
- 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.
The prizes for the 6-round series in 2020:
- In each round top-100 participants get points according to the table.
- The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
- The best 20 participants over all series get sweatshirts and place certificates.
Thanks to XTX, which in 2020 supported the global rounds initiative!
The problems of this round were prepared by a team of authors: [user:adamant,2020-07-01], [user:anto...
Codeforces Global Round 9, - _As a tester, this round gave me PTSD._ - _As a tester, I am, humor of the round., - In each round top-100 participants get points according to the table. - The
final result for, It is the third round of a 2020 series of [Codeforces Global
Rounds](/blog/entry/65002). The rounds, The prizes for the 6-round series in 2020:, The prizes for this round:, The problems of this round were prepared by a team of authors:
[user:adamant,2020-07-01
Announcement of Codeforces Global Round 9
10.
In Problems Statements, Example Inputs Are Now Highlighted if Test Cases Are Used <img src="/predownloaded/c1/64/c164a37e70461b3b6a0236b7e72c81c7f9b47d8d.png" style="width: 200px; float: right; margin: 1em 0 0 0;"/>
Hello, Codeforces.
Look what an interesting thing I've been working on the last few days.
Now, if a problem uses test cases and its validator is written in the recommended way (using setTestCase),
then the example inputs are displayed using different colors.
Just follow the link and see how beautiful it turned out: <a href="https://codeforces.me/contest/1714/problems">https://codeforces.me/contest/1714/problems</a>!
So far I have enabled this only for the last few rounds, but if everything works as intended, I will enable it for more rounds.
In order to support this, I had to tinker a lot. I made changes to [testlib.h](https://github.com/MikeMirzayanov/testlib) so that the validator can return test markup.
Support for this markup required changes in various system services. But I think it's worth it!
The coolest thing is that it wa...
11.
Codeforces: Problem Difficulties Hi Codeforces!
Meet a small innovation on Codeforces — difficulties of problems (and at the same time a new widget filtering problems in the archive). For all the problems of the archive, I’ve calculated the difficulties in the scale of the rating of participants. Approximately this means that if the rating of the problem is equal to yours, then on a typical round you would solve the problem with a probability of 0.5. And, in general, if your rating is $r_i$, and the problem rating is $r_j$, then the problem during the round can be solved approximately with probability:
$$P_{i,j}=\frac{1}{1+10^{\frac{r_j-r_i}{400}}}.$$
For example, if the rating of a problem is less than yours by 200, then the expected probability of solving the problem is 0.75. With a difference of 400 rating points, the probability increases to 0.9.
For convenient search of problems in the archive, you can now use a special widget:
<center><img src = "/predownloaded/1c/fb/1cfba40476423720c79f0f...
of the problem is equal to yours, then on a typical round you would solve the
problem with a, that if the rating of the problem is equal to yours, then on a typical round
you would solve the
12.
Hello 2018 Hello 2018!
If you're still thinking what to do on the eighth day of year 2018, pay attention! The first round for both divisions of the new year starts on January 8 at 17:35 Moscow time ([what about other timezones?](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Hello+2018&iso=20180108T1735&p1=3396&ah=2&am=30)).
Four important components of Hello 2018 will be the same as in Good Bye 2017:
- Div1 + Div2 combined
- 8 problems
- 2 hours 30 minutes
- Rated
But there will also be a substantial difference:
- Different problems
The problems of this round have been proposed and prepared by [user:YakutovDmitriy,2018-01-06], [user:BudAlNik,2018-01-06] and myself.
Thanks to everyone without whom this round wouldn't be possible as well: [user:AlexFetisov,2018-01-06], [user:Golovanov399,2018-01-08], [user:KAN,2018-01-06], [user:MikeMirzayanov,2018-01-06], [user:PavelKunyavskiy,2018-01-06], [user:qwerty787788,2018-01-06], [user:VArtem,2018-01-07], [user:winger,20...
! The first round for both divisions of the new year starts on January 8 at
17:35 Moscow time ([what, If you're still thinking what to do on the eighth day of year 2018, pay
attention! The firstround, Thanks to everyone without whom this round wouldn't be possible as well:
[user:AlexFetisov,2018-01, The problems of this round have been proposed and prepared by
[user:YakutovDmitriy,2018-01-06
Announcement of Hello 2018
13.
Codeforces Round #810 Editorial Sorry for the late editorial. May this editorial help you. If you have questions, feel free to ask.
[problem:1711A]
<spoiler summary="hint1.">
The minimal weight is at least $1$ since $1$ divides any integer (so $1$ divides $p_1$).
</spoiler>
<spoiler summary="solution">
Since $k+1$ does not divide $k$, a permutation with weight equal to $1$ is: $[n,1,2,\cdots,n-1]$.
</spoiler>
<spoiler summary="code">
~~~~~
#include <bits/stdc++.h>
using namespace std;
void work()
{
int n;
cin>>n;
cout<<n<<' ';
for (int i=1;i<n;i++)
cout<<i<<' ';
cout<<endl;
}
int main()
{
int casenum=1;
cin>>casenum;
for (int testcase=1;testcase<=casenum;testcase++)
work();
return 0;
}
~~~~~
</spoiler>
[problem:1711B]
<spoiler summary="hint1.">
See the party as a graph.
</spoiler>
<spoiler summary="hint2.">
Divide the vertices into two categories according to their degrees' parity.
</spoiler>
<spoiler summary="solution">
Let's consider ...
Codeforces Round #810 Editorial
Tutorial of Codeforces Round 810 (Div. 1)
Tutorial of Codeforces Round 810 (Div. 2)
14.
Rule Restricting the Use of AI [revision 2024-09-14] It seems that neural networks are working technological wonders. Not long ago, they struggled with even the simplest tasks in our competitions, but now they are reaching new heights that cannot be overlooked.
There is reason to believe that progress will continue, and we can expect further advancements in neural networks within the realm of programming competitions.
For this reason, we are explicitly limiting the use of AI-based systems (such as various models like GPT, Gemini, Gemma, Llama, Claude, and others) for solving programming problems.
However, we recognize that AI can be a valuable tool for learning and coding assistance, so we aim to establish clear boundaries for its use.
**Application of this Rule:**<br/>This rule applies strictly to in-contest participation. This includes both registered contestants and out-of-competition participants in any rated Codeforces round. If a round is unrated and this is explicitly stated in the round announcement or rules, the rul...
includes both registered contestants and out-of-competition participants in
any rated Codeforcesround, the internet prior to the competition round, this will be considered evidence
of cheating. This, round. If a round is unrated and this is explicitly stated in the round
announcement or rules, the
15.
Codeforces: Soon We Will Change the Rating Calculation for New Accounts Hello everyone.
In the coming days I will finish the implementation of small changes in the rating calculation for new accounts. Here are the main innovations.
* The rating of the new account will be equal to $0$ for display (but it will be equal to $1400$ when calculating rating changes).
* Suppose, after the first round, the participant gained $d_1$ rating points (remember that the rating was considered equal to $1400$ in such calculations), then in the rating display after this round $500+d_1$ will be displayed. Thus, after the first participation, the rating is likely to increase from $0$ to a value in the region of $500$ (plus or minus $300$ approximately).
* Thus, before the second participation, the displayed rating is $500+d_1$, and the rating for calculating changes is $1400+d_1$. Suppose a new change is $d_2$, then the displayed rating becomes $500+d_1+350+d_2$.
* Thus, before the third participation, the displayed rating is $500+d_1+350+d_2$, and the rating for calc...
$ when calculating rating changes). * Suppose, after the first round, the
participant gained $d_1, ). * Suppose, after the first round, the participant gained $d_1$ rating points
(remember that the
16.
Rounding 2025 Hi Codeforces!
2025 comes to an end. However square the year was, we held a number of rounds: 29 Div. 1 and 31 Div. 2-only contests, to be precise! Additionally, 18 Div. 3, 4 Div. 4, and 13 Educational rounds made the schedule even more congested.
<img src="/predownloaded/c8/54/c854d6a423b830263449cca6ff841c8e4e02e024.png" style="width:1400px; float:center; margin: 1em 1em 1em 1em"/>
December is not only the <strike>perfect</strike> [only](/blog/entry/149140?#comment-1332941) time to wrap the year, but also to celebrate and thank all the people who made this year possible. That's why I want to highlight with this post the people whose efforts shaped Codeforces contests.
I'd like to say a huge thank you to every active community member who created and/or prepared problems for Codeforces rounds! Without your ideas and creativity, it would be impossible to hold so fun and interesting competitions. There are so many of you from every corner of the world, so that it's impossible...
[user:Um_nik,2025-12-31] who now pre-reviews all round proposals, making sure
the authors receive, -12-31] who now pre-reviews all round proposals, making sure the authors
receive timely feedback. At
17.
VK Cup 2017 Round 3 + Codeforces Round #412 (Div. 1 + Div. 2) Hi everyone!
The last elimination round of VK Cup 2017, Round 3, will take place on May 7 at 18:35 MSK ([check your timezone here](https://www.timeanddate.com/worldclock/fixedtime.html?msg=VK+Cup+Round+3&iso=20170507T1835&p1=352&ah=3)), along with separate Codeforces Round #412 for both divisions. All three rounds will be three hours long, and all three rounds will be rated.
The contest "VK Cup 2017 — Round 3" is for teams qualified from Round 2 or Wildcard Round 2. The top 20 teams will advance to the final which will be held in July 2017 in Saint Petersburg!
Huge thanks to [user:KAN,2017-05-06], [user:qwerty787788,2017-05-06], [user:PavelKunyavskiy,2017-05-06], [user:AlexFetisov,2017-05-07], [user:MikeMirzayanov,2017-05-06], and VK company for making this round possible.
Codeforces will be the main character of most problems. Don't forget that it's useful to read the statements of all the problems.
Good luck!
As we're in year 2017, the scoring will obviously be stat...
VK Cup 2017 Round 3 + Codeforces Round #412 (Div. 1 + Div. 2), announced before the round., this round possible., +Round+3&iso=20170507T1835&p1=352&ah=3)). Параллельно с ним на тех же задачах
состоится CodeforcesRound, /fixedtime.html?msg=VK+Cup+Round+3&iso=20170507T1835&p1=352&ah=3)). Параллельно
с ним на тех же задачах состоится, Hi everyone! The last elimination round of VK Cup 2017, Round 3, will take
place on May 7 at 18, The contest "VK Cup 2017 — Round 3" is for teams qualified from Round 2 or
WildcardRound 2. The, The last elimination round of VK Cup 2017, Round 3, will take place on May 7 at
18:35 MSK ([check, VK Cup Round 3:
18.
Hello 2024 Hello Codeforces,
We are very glad to invite you to participate in [contest:1919], which will start on [contest_time:1919]. You will be given **8 problems** and **2.5 hours** to solve them. One of the problems will be divided into two subtasks. The round will be rated for everyone. There will be at most 2024 interactive problems, so please read the [guide for interactive problems](https://codeforces.me/blog/entry/45307) before the contest.
All the problems are written and prepared by me.
<spoiler summary="Spoiler">
The first tester tested on 10 October **2022**.
</spoiler>
We would like to give our sincere thanks to:
- [user:errorgorn,2024-01-02] for his wonderful coordination!
- [user:Alexdat2000,2024-01-02] for translating problem statements.
- [user:dario2994,2024-01-02] for coming up with the solution to one of the problems.
- [user:conqueror_of_tourist,2024-01-02], [user:iLoveIOI,2024-01-02], [user:Um_nik,2024-01-02], [user:oolimry,2024-01-02], [user:thenymphs...
divided into two subtasks. The round will be rated for everyone. There will be
at most 2024, testing the round. - [user:dantoh,2024-01-02], [user:Myrcella,2024-01-02],
[user:dario2994,2024-01-02, the problems will be divided into two subtasks. The round will be rated for
everyone. There will be, Hope everyone will enjoy the round!
Announcement of Hello 2024
19.
AlphaCode (DeepMind) Solves Programming Problems on Codeforces <img src="/predownloaded/99/08/99083f12762004fb2f7278177262dd577e3f19cd.png" style="float:right; width:300px; margin:0;"/>
Hello, community.
Today DeepMind announced a new achievement of AI. And it is directly related to what we love — programming problems.
They have developed AI capable of solving some competitive programming problems! The future has arrived.
You should read solutions of [user:SelectorUnlimited,2022-02-02], [user:WaggleCollide,2022-02-02], and [user:AngularNumeric,2022-02-02] solutions. All solutions are written automatically. The only input for writing solutions is a problem statement in English.
Details can be read at the link https://deepmind.com/blog/article/Competitive-programming-with-AlphaCode
Apparently, if these accounts would take part in real competitions, then their rating would be about 1300.
<center>
<img src="https://i.blogs.es/a2119c/terminator-2/1366_2000.jpg" style="width:450px;"/><br>
<small>Terminator is ready to take p...
part in Codeforces Round #770 (Div. 2) In 1997 Kasparov played against (and, > Terminator is ready to take part in Codeforces Round #770 (Div. 2)
20.
Codeforces Round #639 Hello, Codeforces!
I'm very glad to invite you to [contest:1344] and [contest:1345]. This contest will take place on [contest_time:1344]. In both divisions, you will have **2 hours 15 minutes** to solve **6 problems**. The score distribution will be announced closer to the start of the contest.
Of course, this round would not be possible without the help of many people, who I'd like to thank:
- [user:isaf27,2020-05-01], for coordinating this round, and helping with solution ideas.
- My ICPC teammates [user:Kuroni,2020-05-01] and [user:strongoier,2020-05-01], and coach [user:cn355,2020-05-01], for encouraging me to pursue competitive programming. In particular, I'd like to thank [user:Kuroni,2020-05-01] for being so spectacularly bad that a barely-orange user like myself actually has a place on our team.
- [user:300iq,2020-05-01], [user:antontrygubO_o,2020-05-01], [user:Ari,2020-05-01], [user:ffao,2020-05-01], [user:fpc_coder,2020-05-01], [user:gamegame,2020-05-01], [user:Kur...
Codeforces Round #639, grateful that the issue was detected early instead of arising in the middle of
theround. On the, problems, and I hope you enjoy the round. Good luck!, - [user:isaf27,2020-05-01], for coordinating this round, and helping with
solution ideas. - My, . Of course, this round would not be possible without the help of many people,
who I'd like to, Of course, this round would not be possible without the help of many people,
who I'd like to thank:
Announcement of Codeforces Round 639 (Div. 1)
Announcement of Codeforces Round 639 (Div. 2)
21.
Codeforces Round #639: the round is rescheduled Hello, Codeforces!
Unfortunately, I report that I decided to reschedule this round. I'm afraid that something might go wrong. Some strange database behavior has appeared, which leads to slow operation in completely unexpected places (it never was and should not be). I will work hard to fix it. My recent tests show that this can dramatically increase judging time (and leads to a huge queue). I don't want to risk the efforts of the writer, the coordinator, testers, and your time. Sorry about it, I was trying to fix it for many hours but I need more time. Hope it will be a great round!
Mike.
**UPD 1:** I temporarily rescheduled it on May, 6. But I'll discuss the date with the writer and coordinator and reschedule it again to the date they want.
**UPD 2:** [user:Monogon,2020-05-04] approved that [contest_time:1345] is good new date and time for the round. See you in 3 days!
**UPD 3:** It seems I've fixed the issue. It turned that it was connected with [week ago incident](htt...
Codeforces Round #639: the round is rescheduled, for the round. See you in 3 days!, Hello, Codeforces! Unfortunately, I report that I decided to reschedule this
round. I'm afraid, Unfortunately, I report that I decided to reschedule this round. I'm afraid
that something might go
22.
Telegram Returns as Title Sponsor of Codeforces! <img width="200px" src="https://assets.codeforces.com/images/telegram-logo.svg" style="width:200px;max-width:200px;float:right; margin: 0 1em 1em 1em"/>
Hi, Codeforces!
I have some great news. But maybe you've already noticed? Seen the updated logo?
I'm glad to announce that Telegram is back as our title sponsor. I'm happy, and not just because this means we can keep developing and maintaining the system and (most importantly) running rounds for a long time to come.
But there's something else, too. It was Pavel Durov who, way back in 2010, spent several hours asking questions and trying to understand what I had in mind. Then he put his faith in our community — and Codeforces received support for the very first time. That support helped us for many years. So this means a lot to me personally, and I'm proud that now, more than 16 years after that first conversation, that support is coming back.
This helps with every round we run and gives us a chance to do new things, too....
support is coming back. This helps with every round we run and gives us a
chance to do new things, too, This helps with every round we run and gives us a chance to do new things, too.
I'm glad to share
23.
Codeforces: Our Steps After DDOS Attack Hello.
As I wrote into a comment, last round we are faced with a strong DDOS-attack which ruined the competition. I don't know who did it, I also don't know reasons to do it. I'm very upset about the situation and ready to make an effort to be prepared for such issues.
I spend a lot of time to be ready for such incidents.
Here are steps you need to do to be ready for unexpected failures:
* Join our telegram channel by the link https://t.me/codeforces_official to read urgent news.
* Be sure that you know the password of your Codeforces account. If you don't remember it, just use <a href="https://codeforces.me/passwordRecovery">the password recovery feature</a>. Please, do it right now.
* I've implemented a minimalistic website for replacing the main site in case of emergencies. Now you can only read problems, view your submissions (without any details), submit codes. Probably, later I'll add some more features, but anyway, the minimalistic version will have only vital fea...
As I wrote into a comment, last round we are faced with a strong DDOS-attack
which ruined the, Hello. As I wrote into a comment, last round we are faced with a strong
DDOS-attack which ruined
24.
Codeforces celebrates its 15th anniversary! <img src="https://assets.codeforces.com/files/codeforces15.jpg" style="width:250px; float:right; margin: 0 1em 1em 1em;" />
Hi, Codeforces!
Around this time, 15 years ago, I was deploying the first version of Codeforces on a server, registering my account, and writing the first post. 15 years have passed. Well, happy anniversary to us!
For me, this is the most exciting adventure — full of ups and downs, hard work, and moments of joy. What's amazing is that it was never a lonely journey. I've always had caring and reliable friends by my side! That includes the Codeforces team, coordinators and problem writers, our partners in various events, all community members, and, of course, our sponsors — steadfast supporters and helpers.
Look at what we've accomplished together! Here are some of the key metrics over the years. There seems to be plenty to celebrate!
<center>
<img src="https://assets.codeforces.com/files/15/01-submissions.png" class="resource" style="width:300px;"/>...
all want to see new and exciting problems and regular rounds. Now, Div 1 + Div
2round authors will, coordinators. We all want to see new and exciting problems and regular rounds.
Now, Div 1 + Div 2round, off soon—or perhaps we'll wait for the next round binary date at 16 years!
25.
Codeforces Round 1119 (Div. 3) <pre><code class="cpp">#include "codeforces.h"
#include <chrono>
#include <vector>
using namespace std;
using namespace std::chrono_literals;
using namespace cf;
int main() {
Blog announcement("Codeforces Round 1119 (Div. 3)");
announcement << "Hello Codeforces!\n";
announcement << "I am delighted to invite you to participate in " << </code>[contest:2259]<code class="cpp"> << "!\n";
announcement << "The problems were written and prepared by " << </code>[user:nik_exists,2026-09-01]<code class="cpp"> << ".\n\n";
announcement << ContestInfo {
.start_time = </code>[contest_time:2259]<code class="cpp">,
.duration = 2h + 15min,
.number_of_problems = 7,
.subtasks = true // possibly not adjacent
};
announcement << RatingRules {
.rated_for_rating_below = 1600,
.unrated_registration_allowed = true,
.trusted_max_rating_...
Codeforces Round 1119 (Div. 3)
Announcement of Codeforces Round 1119 (Div. 3)
26.
Codeforces Round #735 (Div. 2) কি অবস্থা মামা? (That's Bengali for "What's up dude?")
I am super excited to invite you to participate in [contest:1554] which will be held on [contest_time:1554]. This round is rated for future LGM participants whose current rating is $\le 2099$.
You will be given $5$ problems and $2$ hours to solve them. All the problems are authored and prepared by me.
I would like to thank -
- [user:antontrygubO_o,2021-07-20] for his awe-inspiring coordination of the round <i style="color:White;"> and rejecting my problems, and thus hurting my feelings.</i>
- [user:Um_nik,2021-07-20], [user:_Ash__,2021-07-25], [user:Anachor,2021-07-20], [user:Arg_007,2021-07-20], [user:Alpha_Q,2021-07-20], [user:DAleksa,2021-07-20], [user:steinum,2021-07-20], [user:tasdid,2021-07-20], [user:border,2021-07-20], [user:mk_Shahriar,2021-07-20], [user:t17,2021-07-20], [user:imAnik,2021-07-20], [user:Alfeh,2021-07-20], [user:Aritra741,2021-07-20], [user:FrozenBlood,2021-07-20], [user:SajidZakaria,2021-07-20]...
Codeforces Round #735 (Div. 2), [contest_time:1554]. This round is rated for future LGM participants whose
current rating is $\le 2099$., participate in [contest:1554] which will be held on [contest_time:1554]. This
round is rated for future, - [user:antontrygubO_o,2021-07-20] for his awe-inspiring coordination of the
round
Announcement of Codeforces Round 735 (Div. 2)
27.
Hello 2019 Hello coders! I hope that you are enjoying the New Year as much as me. To make its beginning even greater, Codeforces is going to host a contest and I will be an author of all tasks. Hello 2019 will take place on [Friday](https://www.timeanddate.com/worldclock/fixedtime.html?day=4&month=1&year=2019&hour=17&min=35&sec=0&p1=166).
Using the opportunity, I want to thank to:
- [user:lewin,2019-01-02] and [user:mnbvmar,2019-01-02] for testing the round.
- [user:mnbvmar,2019-01-02] for indescribably helpful discussions about problems.
- [user:_kun_,2019-01-02] and [user:KAN,2019-01-02] for round coordination and help with preparation.
- [user:MikeMirzayanov,2019-01-02] for such great platforms (you know which ones :P).
The round will consist of 8 problems and you will be given <s>two and a half</s> three hours to solve them. Yes, the round will be **rated**.
There will be no interactive problems, but if you want you can read [this](https://codeforces.me/blog/entry/45307) docum...
**UPD4:** The round will be **3 hours** long., **UPD6:** The round is over, congratulations to the winners!, - [user:lewin,2019-01-02] and [user:mnbvmar,2019-01-02] for testing the round.
- [user:mnbvmar, -01-02] and [user:mnbvmar,2019-01-02] for testing the round. -
[user:mnbvmar,2019-01-02] for, The round will consist of 8 problems and you will be given two and a half three
hours to
Announcement of Hello 2019
28.
Codeforces: Updates in rating and rounds <img src="/predownloaded/21/a3/21a33b497ee8a34a678befc3f79745eb69a9cf07.png" style="float:right; margin: 0 1em 1em 1em;"/>
Hello, Codeforces!
It's time for news. I hope you will enjoy!
* We reduce the rating bound for the orange color. Thus, now the orange rating (and the _Master_ title) will start from 2100 rating units.
* The lower bound of the rating for _legendary grandmasters_ is increased to 3000 rating units. Thus, right now in the community, 14 participants meet this requirement. Real legends!
* For rounds like "Div. 2 Only" the upper bound of the rating for official participation is increased. Now everyone whose rating is less than 2100 (i.e., before _masters_) will be able to register for such rounds to participate officially, their rating will be updated based on the results of the round. We do not plan to increase the complexity of Div. 2 rounds. Practice shows that the problems of such rounds are interesting and useful for participants "below the orange".
...
than 1600 at the time of the start of a round. Perhaps we will experiment with
the definition of who, the results of the round. We do not plan to increase the complexity of Div. 2
rounds. Practice, . 1 edition of the round continue to include participants with the rating from
1900 and above., round. We do not plan to increase the complexity of Div. 2 rounds. Practice
shows that the problems of
29.
My opinion on how to practice competitive programming I'm not very often replying to questions about how to practice, but as I'm getting enough of them (and I've just seen another blog about practicing) let me tell you about it.
Of course, every time when you ask someone good about how to practice, he/she will reply to you to "solve a lot of problems" and that's true, there's no other way. Anyway, I've thought about it and actually I'm able to tell a bit more. I know some people, I've seen many people practicing (including me) and I have an opinion.
Many people practice in some organized way. High schools organize IOI/OI training contests every Saturday, universities organize ICPC training contests once a week, people try by their own to solve three problems each day, websites host rounds and so on. Here's a secret: it's a sh*t. Yep, that's true. If you want to be really good and to make it happen you compete in a training once a week, you do it only to be able to make excuses "but I'm training so hard" when you see no progress.
...
). Or you want to upsolve a whole round (still can be a challenge for you). Or
you want to have more, Do you want to participate in a virtual round? Sure, go and do this. Don't do
this if you are sure
30.
Goodbye 2020. Hello 2021! <img src="/predownloaded/f4/1f/f41ff0beb745fb2f84a55d9f2cc451273efc6267.jpg" style="width:300px; float:right; margin: 0 1em 1em 1em"/>
Hello Codeforces!
This unusual and difficult 2020 has come to an end! What will the new year be like?
I wish all of us that we have the opportunity to meet in person so that the contests take place not only online.
I ask you to think of something important and good. Let this wish come true!
We have had a large number of rounds this year. I hope we have pleased you with interesting problems.
Thanks to the round coordinators and writers! You make our community richer. Please make us happy in 2021!
I wish the participants victories over yourself (and over problems!) and development of your skills, interest and curiosity!
Hello, 2021!
And we have traditional gifts!
#### <img src="https://assets.codeforces.com/images/wand.png"/> Change Handle Feature
Hurry! Only until the 10th of January, you can change your handle (<b>but only onc...
problems. Thanks to the round coordinators and writers! You make our community
richer. Please make us
31.
Codeforces Round #635 _Riichi...Tsumo! 2 han 2000 points!_
Hi! Have you ever heard of the game called _Mahjong Soul_? It is a Japanese Mahjong game that is famous for the adorable characters.
We are excited to invite you to take part in [Codeforces Round #635](https://codeforces.me/contests/1336,1337), where you can help the characters in trouble. This round will be held on [contest_time:1336]. Most importantly, it is **rated** for both divisions!
Each division will be given **6 problems** and you will have **2.5 hours** to solve them. An interactive problem may be found in this round. If you are not familiar with interactive problems, you can learn about them [here](https://codeforces.me/blog/entry/45307).
The problems were prepared by [user:EternalAlexander,2020-04-14], [user:ustze,2020-04-14] and me [user:Sooke,2020-04-14].
We sincerely thank [user:isaf27,2020-04-14] for reviewing and coordinating the round, and ...
Codeforces Round #635, interactive problem may be found in this round. If you are not familiar with
interactive problems, you, We are excited to invite you to take part in [Codeforces Round
#635](https://codeforces.com, We sincerely thank [user:isaf27,2020-04-14] for reviewing and coordinating the
round, and
Announcement of Codeforces Round 635 (Div. 1)
Announcement of Codeforces Round 635 (Div. 2)
32.
Codeforces Round #646 (Div. 2) Hi everyone!
I would like to invite you to my fourth Codeforces Round, which I have made with my friends [user:FastestFinger,2020-05-29] and [user:TheOneYouWant,2020-05-29]. In terms of problems, it is my favorite among all my rounds.
With that said, I bring to your attention our new [contest:1363] that will take place on [contest_time:1363]. If your rating is less than **2100**, this round will be rated for you; otherwise, you can participate out of competition.
I would really like to thank:
- [user:FastestFinger,2020-05-29] and [user:TheOneYouWant,2020-05-29] for helping with preparing problems and giving new ideas.
- [user:antontrygubO_o,2020-05-29] for coordinating our round
- [user:300iq,2020-05-29], [user:Jeel_Vaishnav,2020-05-29], [user:Ari,2020-05-29], [user:aryanc403,2020-05-29], [user:mahmoudbadawy,2020-05-29], [user:Vivek1998299,2020-05-29], [user:Uzumaki_Narutoo,2020-05-30], [user:Bakry_,2020-05-31], [user:smartnj,2020-05-30] and [user:Nikhil_Medam,2020-05-29]...
Codeforces Round #646 (Div. 2), [contest_time:1363]. If your rating is less than **2100**, this round will be
rated for you; otherwise, you, problems and giving new ideas. - [user:antontrygubO_o,2020-05-29] for
coordinating ourround - [user, Hi everyone! I would like to invite you to my fourth Codeforces Round, which I
have made with my, I would like to invite you to my fourth Codeforces Round, which I have made
with my friends
Announcement of Codeforces Round 646 (Div. 2)
33.
I Love CF I miss the old CF, Anton rounds cold CF
Textbook sized blogs CF, no cheater blogs CF
I hate the new CF, the captcha hell CF
No Div 1s scheduled CF, just endless Div 4s CF
I miss the sweet CF, debug till sleep CF
I gotta say pre-GPT I’d like to meet CF
See we invented CF, it wasn't any CF
And now I look and look around just AI cheaters CF
I used to love CF, I used to love CF
I even made the rounds, I thought I was CF
What if CF made a blog about CF
Called “I Miss the Old CF," man that would be so CF
That’s all it was CF, we still love CF
And I love you like CF loves CF
34.
Codeforces Round #658 Hello, Codeforces!
I'm very glad to invite you to [contest:1381] and [contest:1382]. This contest will take place on [contest_time:1381]. In both divisions, you will have **2 hours** to solve **5 problems** (and one subtask). The score distribution will be announced closer to the start of the round.
Huge thanks to:
- [user:isaf27,2020-07-19] for excellent coordination of this round
- [user:Andreii,2020-07-19], [user:antontrygubO_o,2020-07-19], [user:Ari,2020-07-19], [user:DeadlyCritic,2020-07-19], [user:gamegame,2020-07-19], [user:growup974,2020-07-19], [user:hugopm,2020-07-19], [user:Kuroni,2020-07-19], [user:NooB_MB,2020-07-19], [user:Priyank,2020-07-19], [user:SecondThread,2020-07-19], [user:--Someone--,2020-07-19], [user:talibmohd,2020-07-19], [user:WNG,2020-07-19] for testing the problems and providing useful feedback.
- [user:MikeMirzayanov,2020-07-19] for providing Codeforces and Polygon platforms.
I've worked hard to ensure the pretests are short and the statement...
Codeforces Round #658, subtask). The score distribution will be announced closer to the start of the
round., - [user:isaf27,2020-07-19] for excellent coordination of this round -
[user:Andreii,2020-07-19, round. Huge thanks to: - [user:isaf27,2020-07-19] for excellent coordination of
thisround
Announcement of Codeforces Round 658 (Div. 1)
Announcement of Codeforces Round 658 (Div. 2)
35.
Codeforces Round #648 (Div. 2) Hi everyone!
I would like to invite you to my fifth Codeforces Round, that I set with my friends [user:FastestFinger,2020-06-05], [user:Vivek1998299,2020-06-05] and [user:ridbit10,2020-06-05].
We are excited to bring another contest within a week :D
With that said, I bring to your attention our new [contest:1365] that will take place on [contest_time:1365]. If your rating is less than **2100**, this round will be rated for you; otherwise, you can participate out of competition.
I would really like to thank:
- [user:FastestFinger,2020-06-05], [user:Vivek1998299,2020-06-05] and [user:ridbit10,2020-06-05] for helping with preparing problems and giving new ideas.
- [user:300iq,2020-06-05] for coordinating our round.
- [user:Um_nik,2020-06-06], [user:antontrygubO_o,2020-06-05], [user:ksun48,2020-06-05], [user:Jeel_Vaishnav,2020-06-05], [user:aryanc403,2020-06-05], [user:FlowerOfSorrow,2020-06-05], [user:KonaeAkira,2020-06-05], [user:_Aaryan_,2020-06-05], [user:Ari,2020-06-...
Codeforces Round #648 (Div. 2), [contest_time:1365]. If your rating is less than **2100**, this round will be
rated for you; otherwise, you, our round. - [user:Um_nik,2020-06-06], [user:antontrygubO_o,2020-06-05],
[user:ksun48,2020-06-05, Hi everyone! I would like to invite you to my fifth Codeforces Round, that I
set with my friends, I would like to invite you to my fifth Codeforces Round, that I set with my
friends
Announcement of Codeforces Round 648 (Div. 2)
36.
Good Bye 2025 <div style="overflow:hidden;">
<img src="/predownloaded/a2/4f/a24f8db165991fb983fc766d223782cbf2785f7f.png"
style="float:right; width:200px; height:auto; margin-left:50px; margin-right:50px; border-radius:0px;" />
<h2>Merry Christmas, Codeforces! 🎄 🎄 🎄</h2>
<p>
We are glad to invite you to take part in [contest:2178], which will start on [contest_time:2178]. You will be
given <b>9 problems</b> and <b>3 hours</b> to solve them. <b>At least one problem will be interactive</b>, so please make sure to read the <a href="https://codeforces.me/blog/entry/45307">guide for interactive problems</a> before the contest. This round is open and rated for everyone.
</p>
<p>
Problems are authored by [user:conqueror_of_tourist,2025-12-25], [user:twosquares,2025-12-25], and [user:YuukiS,2025-12-25].
</p>
<p>
We would like to thank:
</p>
</div>
<div style="clear:both;"></div>
- [user:Error_Yuan,2025-12-...
](/profile/) for participating in this round.
Announcement of Good Bye 2025
37.
Codeforces Global Round 14 Hi!
On [contest_time:1515], we will host [contest:1515]. **<img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width: 200.0px;float: right;margin: 0 1.0em 1.0em 1.0em;max-width: 100.0%;max-height: 100.0%;">**
This is the second round of the 2021 series of [Codeforces Global Rounds](https://codeforces.me/blog/entry/65002). The rounds are open and rated for everybody.
The prizes for this round:
- 30 best participants get a t-shirt.
- 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.
The prizes for the 6-round series in 2021:
- In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT).
- The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
- The best 20 participants over all series get sweatshirts and place certificates.
Thanks to XTX, which in 2021 supported the global rounds i...
Codeforces Global Round 14, Huge thank you to everyone who made this round possible:, The prizes for the 6-round series in 2021:, The prizes for this round:, This is the second round of the 2021 series of [Codeforces Global
Rounds](https://codeforces.com
Announcement of Codeforces Global Round 14
38.
Goodbye 74TrAkToR + Problem A~E: The problems themselves are good and typical A~E. Indeed I like problem D. The pretest for A is a bit weak, and it's not a big problem yet.
+ Problem F: The problem has an origin. :) See the link: [click](https://www.luogu.com.cn/problem/P9394). The problem in contest is only a weakened version of the one in Luogu.
+ Problem G: It's said that our great coordinator had not proved the time complexity of the intended solution is correct :) If the authors did, please share it in the editorial. (although this problem is completely beyond my ability :) )
+ Problem H: Oh dear [user:74TrAkToR,2023-12-30], could you please OEIS the sequence before you use the "several-integer-input" problem in
rounds next time? Anyone who copied the first example and opened [https://oeis.org/A286331](https://oeis.org/A286331) could quickly get the formula. And the problem itself is not so hard imo. Anyway, it should not be used in contest, especially for the last problem.
For me pers...
rounds: + Codeforces Round 907 (Div. 2), which has a *2000 problem as Div2F :)
+ CodeforcesRound 880, + [Codeforces Round #873 (Div. 1 &
2)](https://codeforces.me/blog/entry/116091). I didn't, + [Codeforces Round 907 (Div. 2)](https://codeforces.me/blog/entry/121746).
Also, no fatal, + [Nebius Welcome Round (Div. 1 + Div. 2, rated,
t-shirts!)](https://codeforces.me/blog/entry, I was also an author of a previous official round. I completely understand the
efforts the authors
39.
Educational Codeforces Round 91 is ruined and unrated Hello.
Unfortunately, the Educational Codeforces Round 91 round will be unrated and, actually, it was completely ruined. I don’t understand what happened yet. At some point in time, all systems began to work unstably and actually stopped working. So far I have no understanding what happened. You may have to change the schedule for future rounds. Sorry. We have such a black stripe.
Very upset and demotivated.
Mike.
Educational Codeforces Round 91 is ruined and unrated, Hello. Unfortunately, the Educational Codeforces Round 91 round will be unrated
and, actually, Unfortunately, the Educational Codeforces Round 91 round will be unrated and,
actually, it was
40.
Codeforces Round #633 **내가 돌아왔다!** (Hello, Codeforces!)
I am thrilled to introduce you to [Codeforces Round #633](https://codeforces.me/contests/1338,1339). Followings are basic information:
- This contest will take place on [contest_time:1338].
- The round is **rated for all participants** who can understand this announcement. There will be two divisions.
- There are **5 problems** in each division and you will have **2 hours** to solve it.
- Score distribution will be announced later.
Followings are contributors:
- **Authors**: [user:McDic,2020-04-10] (All Div.2 problems and Div.1 D), [user:tzuyu_chou,2020-04-10] (Div.1 E)
- **Coordinator**: [user:antontrygubO_o,2020-04-10]
- **Testers**:
- **Phase 1** (When this round was supposed to be Div.2): [user:dorijanlendvaj,2020-04-10], [user:SoulTch,2020-04-10], [user:pajenegod,2020-04-10], [user:AryaPawn,2020-04-10], [user:Rahul,2020-04-10], [user:mcdx9524,2020-04-10], [user:300iq,2020-04-10], [user:Nemo,2020-04-10], [user:tfg,2020-04-10]...
Codeforces Round #633, I am thrilled to introduce you to [Codeforces Round
#633](https://codeforces.me/contests/1338,1339
Announcement of Codeforces Round 633 (Div. 1)
Announcement of Codeforces Round 633 (Div. 2)
41.
Goodbye 2021. Hello 2022! <img src="/predownloaded/f4/1f/f41ff0beb745fb2f84a55d9f2cc451273efc6267.jpg" style="width:300px; float:right; margin: 0 1em 1em 1em"/>
Hello Codeforces!
Oh yes, 2021 ends! I recently realized that 2022 is pronounced like "2020 too". Not that. I want a completely different year!
Anyway, we did a nice job this year. I hope we have pleased you with interesting problems.
Thanks to the round coordinators and writers! You make our community richer. Please make us happy in 2022!
I wish you all interesting tasks and brilliant solutions! I wish you error-free code and wish us only rated rounds :-)
Hello, 2022!
And we have traditional gifts!
#### <img src="https://assets.codeforces.com/images/wand.png"/> Change Handle Feature
Hurry! Only until the 10th of January, you can change your handle (<b>but only once</b>)! Note that it will be possible to roll back the changes or change the handle again only _after a year_. Be careful what you wish for.
You can change your han...
42.
Testing Round 20 [Communication Problems] Hello Codeforces.
We are introducing a new type of problem which may appear in future Codeforces rounds, called Communication problems!
In these problems, your program would be ran twice, with different input and output formats between the runs. All variables stored in the memory will be lost between runs. However, the information given to you on the first run may be important to you for completing the second run correctly. Therefore, one of the key challenges in these types of problems would be to find a way to use the limited amount of output you are given in the first run to communicate information to the second run. Below shows a flowchart.
<center>
<br/>
<img src="https://i.ibb.co/JWMFpyfY/a-1.png" alt="2025-09-06-12-40-07" border="0" />
<br/>
Flowchart for communication problems
</center>
In these problems, time and memory limits for both runs would be kept separately. For example, if a problem has a time limit of $2$ seconds, you will only get the Time Limit E...
Testing Round 20 [Communication Problems]
Announcement of Testing Round 20 (Unrated, Communication Problems)
Codeforces (c) Copyright 2010-2026 Mike Mirzayanov
The only programming contests Web 2.0 platform
Server time: Oct/19/2026 18:32:56 (g2).
Desktop version, switch to mobile version.
Supported by
