Hi Codeforces!

On Dec/03/2024 09:25 (Moscow time) we will hold Codeforces Round 990 (Div. 1) and Codeforces Round 990 (Div. 2). Note the unusual starting time!

The harder problems of this round are based on the problems from the Final round of Yandex Cup 2024, Algorithms track, that will be held at the same time.

The problems are authored by elshiko, Flyce, MrLolthe1st, sokolow, stepanov.aa, TeaTime, Tikhon228, webmonster, 4qqqq with guest problems from myst-6, Vladithur, BledDest and me.

I'd like to thank daubi, Golovanov399, arbuzick, pperm, orz, AgafonovArtem, Qwerty1232, k1r1t0, Itsmylove1, Sofi_, and errorgorn for testing the problems, tourist for helping with the round, and MikeMirzayanov for the Polygon and Codeforces systems.

Because of official Yandex Cup Finals ends later than the round on Codeforces, the upsolving, solutions, and test cases will be closed until the end of the onsite contest, roughly 3 hours after the end of the Codeforces round. It is also forbidden to discuss the problems publicly until the end of the onsite round. Any comments here concerning the problems will be removed.

Good luck!

UPD: The contest has been delayed to make sure the online contest does not start earlier than the onsite one.

Congratulations to the winners!

Div. 1:

1. jiangly
2. hank55663
3. noimi
4. cxm1024
5. Pyqe

Div. 2:

1. RGB_ICPC8
2. timer2024
3. tietieAM
4. ylzxxx7
5. mion_sonozaki

UPD: You are free to discuss the problems now.

UPD: Editorial.

Hello Codeforces.

Unfortunately a few hours after the end of Round #819 we were pointed out that one of the problems was stolen from another online judge.

Codeforces team strongly condemns such an action from the author. By no means is this acceptable behavior. This is the first and the most important rule of problem making: your problem should be new up to your best knowledge.

A lot of people put lots of effort into creation of every single round. You can find these people mentioned in the announcements and they indeed deserve these acknowledgments. And yet a single cowardly decision can ruin this huge work and experience of thousands of participants.

In this particular case the copied problem was not widely known, and it seems that this made little or no impact on the course of the round. Nevertheless, we stick to the decision that in such case the round cannot be considered successful, and thus no rating changes can be applied. We will also remove the problem from the round and from the problemset as well as blacklist the author.

We hope that this case will be a lesson for future authors and this situation does not repeat in the future.

Hi all!

This weekend, at Dec/12/2021 18:15 (Moscow time) we will hold Codeforces Round 759 (Div. 2, based on Technocup 2022 Elimination Round 3). They are based on problems of Technocup 2022 Elimination Round 3 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup website and take part in the Elimination Round.

The Div.2 edition is open and rated. Register and enjoy the contests!

• The round authors are: Denisson, antonis.white, dimatimoshin23, napstablook, kirill.grachoff
• Thanks Makcum888, snowysecret, stevancv, wxhtzdy, and ijxjdjd for testing.

Have fun!

UPD: congratulations to the winners!

Technocup 2022 - Elimination Round 3

1. LeoPro
2. princebelkovetz
3. DDima
4. pelmenner
5. abdula-mon-fon-alibaba-A

Codeforces Round 759 (Div. 2, based on Technocup 2022 Elimination Round 3)

1. Maria_Akizuki
2. maxlevel_spyofgame
3. zhaojianmin
4. FlameDragon
5. Shawn

The editorial is published.

Hi everyone!

The Final Round of Technocup 2021 starts this Sunday, March 21, 2021 at 13:00 MSK (10:00 UTC)!

For those who want to compete on the same problems, we will hold two regular Codeforces Rounds in the evening: one for the first division, and another one for the second. The rounds are starting at Mar/21/2021 16:20 (Moscow time).

If you are a participant of the official Technocup Finals, you are not allowed to take part in the rounds in the evening. We ask participants of the official Finals not to discuss the problems in open media till evening.

The problems are prepared by: Alexander Golovanov399 Golovanov, Evgenii amethyst0 Belykh, Andrey AndreySergunin Sergunin, Alexey Aleks5d Upirvitskiy, Diego Diegogrc Garcia and me.

Also huge thanks to Bench0310, kokokostya, Um_nik, dorijanlendvaj, brunomont, Stepavly, antontrygubO_o, JinhaiChen, budalnik, wucstdio, golikovnik, kuviman, dantrag, BledDest, Supermagzzz, JettyOller, geranazavr555, divanik, psevdoinsaf, Roms for testing and invaluable comments, and also to antontrygubO_o for the help in holding the mirror rounds.

Good luck!

Congratulations to winners of Codeforces Rounds!

Div. 1:

1. ecnerwala
2. Radewoosh
3. Benq
4. mango_lassi
5. AliShahali1382

Div. 2:

1. qwqc
2. gezlik
3. yanyutao
4. fengqiyuka
5. ykl

Thanks for participation! Editorial.

As you probably know, most of the rounds on Codeforces are created by active community members. We are very grateful to our talented authors from all around the world for bringing their ideas to tens of thousands of competitors, providing fun and learning experience for contestants of every expertise, from beginners to the world's top programmers. This post will cover the steps you need to take propose a round and become a problem writer on Codeforces.

Who can be a problem author

Best problems usually come from the most experienced participants. We have limited resources for rounds reviewing, so to make the process flawless for writers, starting January 1st, 2021, the following requirements for problem authors will be applied:

• rating: 2100 or above, or
• was a writer in the past.

The restrictions may be updated in the future, the post will be updated accordingly. If your round is already in the review status, don't worry, it will be reviewed regardless of the current restrictions.

If you are an experienced writer/jury member in other competitions, please write any current coordinator (listed below) a private message about your wish to prepare a contest and describe your experience in this area.

How to propose a round

If you meet the requirements, you should have the link "propose a contest/problems" in the personal menu on the right sidebar. Click on the link and follow the instructions carefully. Prepare and submit your proposal for a contest and problems.

In some time you will have a coordinator(s) assigned to your contest proposal. They will review your problems and you will discuss the problems with them. Please be active, respond to coordinators' questions in time, make the proposed changes quickly. Codeforces coordinators are very experienced participants and reviewers. Please respect their opinion, and note that they have the highest priority in any decisions on the problems.

Our coordinators are: Aleks5d, errorgorn, irkstepanov, IgorI, Artyom123, 74TrAkToR, ScarletS, Akulyat, TheScrasse, 244mhq, satyam343, Vladithur, and KAN.

You can only propose a whole problemset for a Div 2 or Div 1 + Div 2 round. We don't consider single problems. Also, we don't consider proposals for Div 3/4 or Educational rounds.

How to prepare problems

Problems for Codeforces rounds are prepared in Polygon. It is not recommended to prepare problems before the coordinator's approval, especially if it's the first time you propose a contest.

For each problem you will need to write a clear statement (in English or Russian), code a validator (a program that checks tests' correctness), a checker if necessary (a program that checks output), and of course correct solution. Also, you will need to create tests to check the contestants' solutions on. Your coordinator will do the statement translation if necessary, check your work, and suggests what to change and add if needed.

Before you start working on problems, even if you have experience working with Polygon, you must read these rules. All the work with checkers, validators, interactors, and generators is done with testlib.h library, you can read the introduction by the link and download examples from Polygon. Whenever you have any troubles and/or difficulties, contact your coordinator for help. It is much faster to do something right from the first time, then to do it wrong and then redo it again.

Writers reward

It is interesting and challenging work to invent and prepare problems but is also time-consuming and demanding work. That's why we pay authors for preparing problems for Codeforces. The rewards are:

*If the reward can be paid in cryptocurrency, it might be increased by 25%.

**Sponsored rounds are selected by coordinators from available proposals.

Conclusions

We hope that with your help we will keep the regular stream of regular rounds full of fresh and interesting problems! If you have any questions on how to become a problem writer, ask in the comments. Please note that unrelated or outdated comments in this blog will be cleared once in a while to keep the blog and comments up-to-date.

Hi all!

This weekend, at Nov/29/2020 10:05 (Moscow time) we will hold Codeforces Round 687. It is based on problems of Technocup 2021 Elimination Round 2 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2021 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The problems authors are; amethyst0, eidan, Diegogrc, bensonlzl, JettyOller, antontrygubO_o, and KAN. Thanks to antontrygubO_o and 300iq for their help in coordination. Also huge thanks to testers for their invaluable help: Golovanov399, kalki411, golions, dantrag, Retired_cherry, gigabuffoon, Andres_Alumets, firi., coderz189, Nero, GGMU, K0u1e, Bench0310, dorijanlendvaj, Um_nik, thenymphsofdelphi, Merkurev, kokokostya, wucstdio, smile_boi, abhishhh1!

Have fun!

Thank you for participation! We hope you enjoyed the problems. Congratulations to winners!

Technocup 2021 - Elimination Round 2

1. Kirill22
2. fastmath
3. VEGAnn
4. alexxela12345
5. solver777

Codeforces Round 687 (Div. 1, based on Technocup 2021 Elimination Round 2)

1. ecnerwala
2. ainta
3. Konijntje
4. al13n
5. kort0n

Codeforces Round 687 (Div. 2, based on Technocup 2021 Elimination Round 2)

1. Sharpness
2. iLoveIOI
3. Linqi05
4. xaohu
5. detect

Upd: Rating updates published.

UPD2: The editorial is published.

1119A - Ilya and a Colorful Walk

Author, preparation: 300iq.

1119B - Alyona and a Narrow Fridge

Author, preparation: KAN.

Aleks5d invites you to compete in the shortest solution challenge for this problem. His code (155 bytes):

[n, k], arr = [int(i) for i in input().split()], [int(i) for i in input().split()]
print([i for i in range(n + 1) if sum(sorted(arr[0:i])[::-2]) <= k][-1])

1119C - Ramesses and Corner Inversion

Author, preparation: 300iq.

1119D - Frets On Fire

Author, preparation: cyand1317.

#include <cstdio>
#include <algorithm>

static const int MAXN = 1e5;

static int n, q;
static long long s[MAXN];
static long long t[MAXN];

int main()
{
    scanf("%d", &n);
    for (int i = 0; i < n; ++i) scanf("%lld", &s[i]);

    std::sort(s, s + n);
    for (int i = 0; i < n - 1; ++i) s[i] = s[i + 1] - s[i];
    std::sort(s, s + n - 1);
    for (int i = n - 1; i >= 1; --i) s[i] = s[i - 1];
    s[0] = 0;
    for (int i = 1; i < n; ++i)
        t[i] = t[i - 1] + (s[i] - s[i - 1]) * (n + 1 - i);

    scanf("%d", &q);
    for (int i = 0; i < q; ++i) {
        long long l, r;
        scanf("%lld%lld", &l, &r);
        l = r - l + 1;
        int p = std::lower_bound(s, s + n, l) - &s[0] - 1;
        printf("%lld%c", t[p] + (l - s[p]) * (n - p), i == q - 1 ? '\n' : ' ');
    }

    return 0;
}

1119E - Pavel and Triangles

Author: gen, preparation: 300iq.

1119F - Niyaz and Small Degrees

Author, preparation: 300iq.

1119G - Get Ready for the Battle

Authors: Aleks5d, KAN; preparation: Aleks5d.

1119H - Triple

Author, preparation: RDDCCD.

Hello everyone!

The Final Round of Technocup 2019 starts today, on the March 3, 2019 at 11:00 MSK (08:00 UTC)! To watch live results (only pretests are considered!), follow the link below:

Results of Technocup 2019 Final Round

Congratulations to the winners of Technocup Final Round 2019!

1. Ildar 300iq Gainullin, Russia, Kazan'
2. Semyon cookiedoth Savkin, Russia, Dolgoprudnyy
3. Batyr 998kover Sardarbekov, Kazakhstan, Almaty
4. Alexander scanhex Morozov, Russia, Saint Petersburg
5. Sofia Sonechko Melnyk, Ukraine, Kremenchuk

For those who want to compete on the same problems, we will hold two regular Codeforces Rounds in the evening: one for the first division, and another one for the second. The rounds are starting at Mar/03/2019 18:35 (Moscow time)!

If you are a participant of the official Technocup Finals, you are not allowed to take part in the rounds at evening. We ask participants of the official Finals not to discuss the problems in open media till evening.

Good luck!

The rounds are over. We sincerely apologize for the fail with the mirror rounds, we thought the editorial was only streamed to other sites of the olympiad, not online. You can read MikeMirzayanov's comment about the situation. I hope you enjoyed solving the problems even though they did not affected your rating.

Huge thanks to those people who worked on the problems for you, namely Alexander Golovanov399 Golovanov, Konstantin zemen Semenov, Daria Dashk0 Kolodzey, Mikhail Endagorion Tikhomirov, Ilia irkstepanov Stepanov and Denis Denisson Shpakovskij.

Also thanks to Um_nik, adedalic, demon1999, Roms, cdkrot, cyand1317, BledDest and Errichto for testing the problems, arsor for translating some of them into English, and cdkrot and arsijo for their help in conducting the mirror rounds.

Congratulations to the winners of the mirror rounds!

Codeforces Round 543 (Div. 1, based on Technocup 2019 Final Round)

1. Radewoosh
2. LHiC
3. vintage_Vlad_Makeev
4. natsugiri
5. V--o_o--V

Codeforces Round 543 (Div. 2, based on Technocup 2019 Final Round)

1. Diazzz
2. IhateProgramming
3. Kunal.h
4. galloska
5. deep_savani

Hi!

Tomorrow, at Feb/07/2019 16:35 (Moscow time) we will host Codeforces Global Round 1.

It is the first round of a new series of Codeforces Global Rounds. The rounds are open for everybody, the rating will be updated 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 2019:

• 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.

The problems of this round were developed by a team of authors: _h_, simonlindholm, grphil, vintage_Vlad_Makeev, GreenGrape, budalnik, cdkrot and me. Thanks arsijo and cdkrot for their help in the round's coordination, and also majk, pashka, Jeel_Vaishnav, Ashishgup and Jatana for testing the round!

Good luck!

Congratulations to the winners!

1. tourist
2. Um_nik
3. TLE
4. mnbvmar
5. sunset
6. jqdai0815
7. ksun48
8. molamola.
9. snuke
10. fateice

Editorial.

Hi all!

This weekend, at Dec/23/2018 16:35 (Moscow time) we will hold Codeforces Round 528. It is based on problems of Technocup 2019 Elimination Round 4 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2019 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The round was prepared by Roms, Neon, BledDest, adedalic, awoo, isaf27, Endagorion with coordinator's help from 300iq.

Have fun!

Author, preparation: KAN.

Author, preparation: cdkrot.

Author, preparation: KAN.

Author, preparation: KAN.

Authors: MikeMirzayanov, cdkrot, preparation: cdkrot.

Author, preparation: Neon.

Author, preparation: KAN.

Author KAN, preparation: KAN, 300iq.

Huge thanks to cdkrot and 300iq for discussing the problems and general invaluable help in preparation!

Hi!

Tomorrow, at Nov/25/2018 19:35 (Moscow time) we will host the final round of Mail.Ru Cup 2018. The problems were authored and prepared by Codeforces team: me, Dmitry cdkrot Sayutin, Ildar 300iq Gainullin and Mike MikeMirzayanov Mirzayanov, and also Maxim Neon Mezhcheryakov. Huge thanks to Grigory vintage_Vlad_Makeev Reznikov abd Kamil Errichto Debowski for problems' testing!

This round is the final in the new championship called Mail.Ru Cup, you can learn more about it following the link. The round will be rated for everybody!

After the round we will know who will get the following prizes:

• First place — Apple MacBook Air
• Second and third place — Apple iPad
• Fourth, fifth, sixth places — Samsung Gear S3
• Traditionally, the top 100 championship participants will get cool T-shirts!

In each round, top 100 participants get prize points according to the table. The championship's result of a participant is the sum of the two largest results he gets on the three rounds. The results of the two first rounds are published here. In case of ties in the top six places, they will be broken by the sum of in-round scores in the corresponding (best for the participant) two rounds.

There will be eight problems and two and a half hours to solve them.

Good luck!

P. S. MikeMirzayanov invites everybody to the official Codeforces channel in Telegram: t.me/codeforces_official.

The round has finished, thanks everybody, hope you liked the problems!

Congratolations to the winners of the third round of Mail.Ru Cup 2018:

1. Radewoosh
2. V--o_o--V
3. ch_egor
4. ksun48
5. RAVEman

The results of the Cup will be announced shortly.

The editorial is here.

Hi all!

This weekend, at Nov/18/2018 19:05 (Moscow time) we will hold Codeforces Round 522. It is based on problems of Technocup 2019 Elimination Round 3 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2019 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The round was prepared by Alexander Golovanov399 Golovanov, Evgeny WHITE2302 Belyh, Alexandra demon1999 Drozdova, Arsenii craborac Kirillov, Ivan ifsmirnov Smirnov, Artem komendart Komendantian, Roman Roms Glazov, Daria Dashk0 Kolodzey and me.

Huge thanks to Grigoty vintage_Vlad_Makeev Reznikov, Ildar 300iq Gainullin, Ilia irkstepanov Stepanov, Andrey AndreySergunin Sergunin for testing.

Have fun!

The round is over, we apologize for the issues with platform accessibility. The round is declared unrated.

Congratulations to the winners!

Technocup 2019 - Elimination Round 3

1. 998kover
2. Kuyan
3. paradox
4. ANTIMIRAGE
5. YaKon4ick

Codeforces Round 522 (Div. 1, based on Technocup 2019 Elimination Round 3)

1. ksun48
2. Anadi
3. LHiC
4. Um_nik
5. mnbvmar

Codeforces Round 522 (Div. 2, based on Technocup 2019 Elimination Round 3)

1. liriKl
2. Moysenko
3. okwedook
4. fauzdar65
5. Bismarck

Thank you all for joining!

The editorial is published.

Hi all!

This weekend, at Oct/21/2018 11:10 (Moscow time) we will hold Codeforces Round 517. It is based on problems of Technocup 2019 Elimination Round 2 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2019 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The round authors are Kostroma, Golovanov399, komendart, Denisson and Dashk0.

Have fun!

The round is over, congratulations to the winners!

Technocup 2019 - Elimination Round 2

1. Holidin
2. receed
3. Sonechko
4. radoslav11
5. scanhex

Codeforces Round 517 (Div. 1, based on Technocup 2019 Elimination Round 2)

1. Radewoosh
2. ainta
3. 300iq
4. TLE
5. RAVEman

Codeforces Round 517 (Div. 2, based on Technocup 2019 Elimination Round 2)

1. cz_yixuanxu
2. orbitingfIea
3. I_Love_Irelia
4. djq_fpc
5. buaads

The editorial is published.

Hi all!

This weekend, at Sep/23/2018 16:05 (Moscow time) we will hold Codeforces Round 512. It is based on problems of Technocup 2019 Elimination Round 1 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2019 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The Elimination Round authors are Roms, BledDest and adedalic. Thanks to Anadi who authored the last problem for div. 1 round and arsijo for his help in coordination. This round would also be not possible without the help of our testers: winger, Um_nik, AlexFetisov, Denisson, thank you so much!

Have fun!

Div. 2 and the Elimination Round will feature 7 problems, preliminary costs are
250 — 500 — 750 — 1500 — 2000 — 2500 — 3000.

Div. 1 will feature 5 problems, preliminary costs are 500 — 1000 — 1500 — 2000 — 2500.

The round is over, congratulations to the winners!

Technocup 2019 - Elimination Round 1

1. 300iq
2. sadovan
3. voidmax
4. karasek
5. ----------

Codeforces Round 512 (Div. 1, based on Technocup 2019 Elimination Round 1)

1. TLE
2. webmaster
3. sunset
4. jcvb
5. volamtruyenkyii

Codeforces Round 512 (Div. 2, based on Technocup 2019 Elimination Round 1)

1. Chair_man_Xi
2. icecuber
3. yp155136
4. xjd0623
5. liyingyan7

The analysis is published.

Hi everyone!

Tomorrow, on the April 29, 2018, at 13:05 UTC we are holding the third round of VK Cup 2018 championship. This is the final online round, the next round is the final round in which top 20 teams from this round advance.

At the same time with the official round, we are holding parallel rounds for both divisions. Join them and see if you can beat top Russian-speaking teams! Top50 in the "Div1 Edition" contest will get t-shirts.

All rounds are rated, their duration is 2.5 hours.

The authors of the problems are Zlobober, Endagorion and me. Thanks qwerty787788 and vintage_Vlad_Makeev for their great help in round preparation!

Good luck!

Congratulations to winners!

1. V--o_o--V, LHiC — solved all problems, two problems ahead the runner-up!
2. craborac, demon1999
3. el_sanchez, SpyCheese
4. Melnik, hloya_ygrt
5. egor_bb, Nikitosh

Mirror for the first division:

1. fateice
2. Petr
3. tourist
4. budalnik
5. TLE

Mirror for the second division:

1. _ChenKerui
2. Hayven
3. poisonous
4. Gold_Three_Fat
5. laofudage

The editorial is here, thanks all for participation!

37617481

37617515

37617552

37617576

37617599

Hi everyone!

Tomorrow, on the April 25-th, 2018 at 17:35 UTC we are holding Codeforces Round 476 (Div. 2) [Thanks, Telegram!]! The round will be rated for the second division participants, members with higher rating can take part out of competition.

I give the floor to MikeMirzayanov to announce the round:

This round opens a series of thanks-rounds to those who significantly supported Codeforces in the crowdfunding campaign for the 8th anniversary. Although Telegram is not explicitly present on the list of donators, for us this is the first and most important friend. We express our gratitude to Telegram and personally to Pavel Durov for the constant support and send regards from programming contest community. Now that the medieval inquisition against Telegram and all the free Internet has been declared in our country, I admire and express support for Pavel's principled position on protecting our rights and freedoms. Thank you, Telegram!

I join the thanks to Telegram, and also want to thank FalseMirror and Livace who helped me with the problems for the round. Also many thanks to vintage_Vlad_Makeev, GreenGrape and 300iq for their help in round preparation, and arsor for translation.

Good luck!

Congratulations to winners!

Div. 2:

1. Akylbeek — solved all problems!
2. kolkulator
3. reeWorld
4. 16bit075
5. teamskiy

Div. 1:

1. uwi
2. quailty
3. bicsi
4. Barichek
5. Adalbert

The analysis is here.

Hi!

Tomorrow, on March 24-th, 2018 at 15:35 UTC we will host the second round of VK Cup 2018 — a programming tournament for Russian-speaking youth. 450 teams that were the best in the first round and the first wild-card round will compete tomorrow. The top 100 teams will advance to the third round directly and get a tournament t-shirt, while the others will have one more chance in the second wild-card round.

For English-speaking community as well as for those who haven't advanced to the second round or haven't participated in VK Cup 2018, we will host parallel Codeforces round for both divisions, as usual. Feel free to take part!

Please note that the tournament is for Russian-speaking people. If you don't speak Russian, you must not compete in the VK Cup round, register for the parallel round instead. Otherwise it is considered as a flagrant violation of rules and might be subject to disqualification and Codeforces ban. Please respect the organizers.

VK Cup 2018 Round 2 and the round for the first division will have six problems each, the second division round will have five of them.

The authors of the problems are cyand1317, skywalkert, Claris and me. Also many thanks to fcspartakm, Tommyr7 for their help in preparation and PavelKunyavskiy, winger, AlexFetisov, Errichto, vepifanov, immortalCO and qwerty787788 for testing the problems! Last but not least, huge thanks to vintage_Vlad_Makeev for his great help in coordinating and testing the round!

Good luck!

The editorial is published!

Congratulations to the winners!

VK Cup Round 2:

1. LHiC, V--o_o--V — solved all problems!
2. egor_bb, Nikitosh
3. -imc-, Golovanov399
4. AllCatsAreBeautiful, arsijo
5. aid

Div. 1:

1. Um_nik
2. Radewoosh
3. ikatanic
4. FizzyDavid
5. jqdai0815

Div. 2:

1. ltf0501
2. Hyperbolic
3. yongshiboshi
4. emengdeath
5. lmhoang

Hi!

Tomorrow, on March 17th, 2018, at 15:35 UTC the first Wild-card Round of VK Cup 2018 will be held. Along with it we will host a parallel unofficial round in which everyone can take part.

The rounds will use special rules, the rounds will be unrated. The problems were prepared by Codeforces team: fcspartakm, MikeMirzayanov and me. Thanks to vovuh, GreenGrape, FalseMirror, Glebodin and vintage_Vlad_Makeev for testing the round and their help to make the round better!

The detailed rules will be added to this post around 30 minutes before the start. There will be 24-hours open hacks phase after the round, like in Codeforces Educational Rounds.

Round rules:

The round will be almost usual contest with ACM ICPC rules. There will be 10 problems for 2 hours. During the round your solutions will be tested on some basic tests, they should be much stronger than usual pretests. After the round you will have 24 hours to find tests against other participants' solutions, this part is the same as in Educational rounds. After that we will add all succesful hacks and our tests and rejudge all submissions. Then the results will be final.

The main difference between ACM ICPC rules and this round is the following rule.

You should submit each problem in a unique programming language. Different compilers of same language are considered the same language. For example, GNU G++, GNU G++ 11, GNU G++ 14 and MS C++ compilers are C++ language. Thus, you are not only to solve problems, but also try different and new for you languages. We don't think you know 10 languages, we hope that you will quickly learn some basic syntax.

Formally, the following check is performed when you submit a task:

• If there is at least one submission in queue or submission that passed at least one test for this problem in another language, your solution will be ignored. Thus, if your program passes at least one test, you can only solve this problem using this language.
• If there is at least one submission in queue or submission that passed at least one test for another problem in same language, your solution will be ignored. Thus, you can't use a language for more than one problem.

Remember that you can view filter status of some other round by language and view submissions in a specific language. Also, you can view examples of codes in any of the supported languages on the table below. Also, the table contains the groups of compilers considered the same language.

You can use "custom invocation" tab to run a solution if you don't have the compiler locally.

The main rules of ACM ICPC contest: each problem can either be completely solved (when all tests are passed), or not solved. The participants are ranked by the number of solved problems, in decreasing order, in case of a tie they are ranked by penalty time. The penalty time is the sum among all problems the time in minutes that had passed between the start of the round and the moment the problem got solved, plus 20 minutes for every rejected submission. Note that the problems are not arranged by difficulty. Also, you can resubmit a solution even if it passed all tests, because there will be more tests after the open hacks.

Good luck!

931A - Friends Meeting

At first understand the fact that friend should make their moves one be one and the friend who initially was left should move to the right and other friend should move to the left. Let len = |a - b|. Then the first friend will make cntA = len / 2 moves, and the second friend — cntB = len - len / 2 moves. So the answer is the sum of two arithmetic progressions cntA·(cntA + 1) / 2 and cntB·(cntB + 1) / 2.

The given constrains allowed to calculate this sums in linear time — simply iterate from 1 to cntA for the first sum and from 1 to cntB to the second.

Thanks GreenGrape for translation!