Hi, Codeforces!

Three years later, first ideas of a contest turned into this complete set of problems, so I am glad to invite you to take part in Codeforces Round #824 (Div. 2), which will take place on Oct/02/2022 17:35 (Moscow time). The round will be rated for the participants with rating lower than 2100. Participants from the first division are also welcomed to take part out of competition.

You will be given 2 hours 15 minutes to solve 6 problems. All the problems were created and prepared by me.

I would also like to thank:

• KAN for awesome coordination!
• Aleks5d, arzhantsev64, ChthollyNotaSeniorious, DanWallgun, flowerletter, Gegege337, Imakf, LeoRiether, mejiamejia, okwedook, PO3OBAR_Bblnb, SSerxhs, TomiokapEace, triple__a, wabadabakalakaboo for testing the round and giving significant feedback.
• mejiamejia for his help with extra testing.
• MikeMirzayanov, geranazavr555, unreal.eugene, DK318, and KAN for maintaining Codeforces and Polygon platforms!

Scoring: $$$500-750-1250-1750-2250-3000$$$.

Note that some problems have similar scores. Your sense of the scoring distribution may differ, don't forget to read further problems if you get stuck.

I look forward to seeing you on the leaderboard. I hope you'll enjoy all 6 problems and wish you good luck!

UPD1: Editorial (problem F will be added later)

UPD2:: Winners and First to solve

Div2

Div1 + Div2

First to solve

Hello, Codeforces Addicts!

On Sep/30/2022 17:35 (Moscow time) we will host Codeforces Global Round 22.

Codeforces Global Round 22 is the $$${\textbf{2}} \cdot {\textbf{2}} = 4$$$-th round of a 2022 series of Codeforces Global Rounds. 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 2022:

• 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 2022 supported the global rounds initiative!

The problems were written and prepared by antontrygubO_o, Milesian and me.

We are extremely grateful to the following people who made this round possible:

• Aleks5d as well as KAN for great coordination.
• lucifer1004 for discussion and being the first tester as this round grows.
• 4qqqq, Akulyat, alexX512, arvindf232, BucketPotato, BurnedChicken, choutii, FairyWinx, Heltion, lucifer1004, lyuankai, mejiamejia, nnv-nick, okwedook, p_b_p_b, Potassium, TomiokapEace, Um_nik, yyt16384, and zjq2863974342 for testing the round and their feedback.
• MikeMirzayanov for creating great platforms Codeforces and Polygon.

Round Information:

• Duration: 2 hours and 30 minutes
• Number of problems: $$${\textbf{2}} \cdot {\textbf{2}} \cdot {\textbf{2}} = 8$$$
• Score distribution: 500 — 1000 — 1500 — 2000 — 2500 — 2750 — 3000 — 4000

Kind Tips:

• Always get ready for interactive problems no matter whether they will exist or not, please see the guide of interactive problems if you are not familiar with it.

We are looking forward to your participation!

UPD. Editorial

Congratulations to the winners!

1. cnnfls_csy

2. ksun48

3. maroonrk

4. orzdevinwang

5. ko_osaga

6. tourist

7. jiangly

8. noimi

9. peti1234

10. Maksim1744

And for the winner of each problem:

A. tourist

B. tourist

C. wind_cross

D. tourist

E. tourist

F. 300iq

G. ksun48

H. rainboy

Hello Codeforces. Hoping you're having a wonderful day! ^_^

DYTECHLAB Cup 2022

This October, we invite you to the first ever Dytechlab Cup 2022 that will start on Oct/07/2022 17:35 (Moscow time). The problems were prepared by members of our company who share a passion for Competitive Programming. It is an open and rated round for both divisions.

The round will have 7 problems and will be 150 minutes long. We wish everyone good luck and have a positive delta!

Prizes

• 1st place: US$200 cash prize
• 2nd place: US$100 cash prize
• 3rd place: US$50 cash prize

Also, we understand that contestants like dope MERCHANDISE, so we are giving away lots of them!

• Top 20 will get a merchandise package which will include: a t-shirt with your Codeforces handle on it, a notebook, 2 pens, and a sports bag.
• 30 merchandise packages, each including a t-shirt & 2 pens will be randomly distributed to 30 contestants ranking 21-200.
• 100 merchandise packages, each including a sports bag & 2 pens will be randomly distributed to 100 contestants ranking 201-1500.

All packages will include stickers in it, so you can stick them to your laptop and show your friends how hardworking you've been :p

Our appreciation goes to

• MikeMirzayanov for the Codeforces and the Polygon platform.
• DmitryGrigorev for coordination of the round.
• magnified for one of the problems and your enthusiastic support in preparing the round.
• ngfam_kongu and updating for 2 problems that fills in the gap to finalize the contest.
• ngfam_kongu, MofK, ladpro98 and every other Dynamic Technology Lab member who helped in coordination, was spot-on while we were working together in the office and helped me come up with ideas for problems.
• The list of testers: KAN, Elite_Vanor, HmmOrange, Kuroni, .DucAnh., LetterC67, nguyentien_zzz, VanIOImaster153, _ngd.nam_, nigus, hank55663, BacHoCuuPikachu, Luminal, kieusontungcva, ehnryx, stevenkplus, MagentaCobra.

Wish you the best and a very positive delta in this round!

About Dytechlab & Job Opportunities

If you are interested in employment opportunities in Eastern Europe, Dubai, or South East Asia, please fill out the contact form below:

We are Dynamic Technology Lab, Pte Ltd. (DTL), a quantitative hedge fund engaging in global securities trading with multiple asset classes. Since our founding in 2009, from humble beginnings in a home garage, we are now a sizable, well-established financial institution with offices in Singapore, Shanghai, Beijing, and Hanoi. Our success is fueled by some of the most inquisitive minds who are relentless in their pursuit of innovation.

As a tech-focused Licensed Fund Management Company under the Monetary Authority of Singapore, DTL is dedicated to producing strong consistent returns for its investors by relying on mathematical and statistical models to drive its investment process.

Right now, we are looking for lots and lots of Engineering positions and are ready to bring opportunities to work in a quantitative trading environment for Engineers of all levels, all around the world!

Learn more about us on this blog or on our website!

Hello Codeforces!

On Sep/29/2022 17:35 (Moscow time) Educational Codeforces Round 136 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 or 7 problems and 2 hours to solve them.

The problems were invented and prepared by Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

Our friends at Harbour.Space also have a message for you:

Hey Codeforces!

Check out our video from our relatively new campus in Bangkok. Harbour.Space@ UTCC Bangkok is located in the heart of this cosmopolitan city where tradition and modernity merge!

We are breaking down boundaries and working together for a better, brighter, tech-driven future!

Bangkok is Southeast Asia's most exciting capital and the number one place for launching a start-up in Asia. Look at our incredible campus and hear from some of our rockstar students!

To find out more about Harbour.Space University, visit https://harbour.space/.

Also, do not forget to follow us on Instagram.

Good luck, Harbour.Space

UPD: Editorial is out

Hello, Codeforces!

We invite you to Codeforces Round #823 (Div. 2) which will be held on Sep/25/2022 17:35 (Moscow time). You will be given 2 hours to solve 6 problems.

The problems were invented and prepared by shnirelman, Lankin and me.

We would like to thank:

• isaf27 for coordinating the round.

• KAN for the help during preparation of the contest.

• kevinxiehk, 74TrAkToR, Aleks5d, cadmiumky, satyam_343, gothic_kobra, NikitaSemenov, tibinyte for testing the round.

• MikeMirzayanov for Codeforces and Polygon.

Wish you good luck and high rating!

The scoring distribution will be announced closer to the beginning of the round.

UPD: Scoring distribution: 500 — 1000 — 1500 — 2250 — 2250 — 3000.

UPD2: Editorial: https://codeforces.com/blog/entry/107293.

UPD3: Winners.

Div1:

1. heno239
2. Um_nik
3. maspy
4. jiangly
5. ksun48

Div2:

1. bip0lar
2. PokerCareer
3. simiao1986
4. i_will_be_less_than_blue
5. Timonnable

UPD: The round has been rescheduled to a different time due to a clash with a CodeChef contest

Hello CodeForces!

Me, happypotato1207 and nicholask are excited to invite you to participate in Codeforces Round #822 (Div. 2). It will start at Sep/23/2022 15:05 (Moscow time). The round will be rated for everyone with less than 2100 rating. You have 2 hours to solve 6 problems. Please note the unusual start time.

We would like to take this opportunity to thank everyone who have contributed to our round:

• darkkcyan for his excellent coordination;
• anthony123 and jerryliuhkg for proposing tasks that did not make it to the final problemset;
• thenymphsofdelphi, kevinxiehk, xuanquang1999, ta4p, ACGN, Mike4235, brianlee.lck, JeffreyLC, prvocislo, ITO, dbsic211 marvinthang, QuangBuiCP, Rekaxem, Alan, sharkycode and OGname, for testing and providing invaluable advice;
• KAN for translating the problem statements into Russian;
• MikeMirzayanov for the marvellous CodeForces and Polygon platforms; and finally,
• You, for participating in this contest!

We look forward to seeing you on the leaderboard!

UPD: Score Distribution: 500 — 750 — 1250 — 2000 — 2250 — 3250

UPD2: Editorial

UPD3: Winners!

Div 1 + 2:

1. GOI_Official
2. Um_nik
3. 822E-Liar
4. Second_Brave_Niuniu
5. hitonanode

Official:

1. GOI_Official
2. 822E-Liar
3. Second_Brave_Niuniu
4. Sand_Emperor
5. steven14414

Hello Codeforces!

We invite you to Codeforces Round #821 (Div. 2) starting on 19.09.2022 17:35 (Московское время). The round is rated for users whose rating is lower than 2100.

All problems were mainly created and prepared by me. One problem is revised by mejiamejia. I would also like to thank:

• MikeMirzayanov for Codeforces and Polygon platforms,
• KAN for helping preparation of the round,
• Arpa for coordinating and reviewing the round,
• mejiamejia for developing one problem and a lot of advices,
• satyam_343, 74TrAkToR, MagentaCobra, cadmiumky, Andreasyan, darkkcyan, Vladithur, Etherite, welleyth, mjhmjh1104, emorgan5289, jeroenodb, oolimry, willy108, uuzlovetree, abc864197532, tibinyte, -skyline-, TomiokapEace, gyh20, SSerxhs, djq_cpp, Lucina, ugly2333, ITO, ak2006 for testing the problems and giving feedback, especially Vladithur for trimming the statement,
• All users for participating in the contest!

You will be given 5 problems with one subtask and 2 hours to solve them. The score distribution will be announced closer to the start of the round.

Good luck, and have fun!

UPD1: Score distribution is 500 — 1000 — 1500 — ( 1500 + 750 ) — 2750.

UPD2: System testing has been finished. Congratulations to the winners!

Out of competition

1. Geothermal
2. SSRS_
3. tabr
4. jiangly
5. tute7627
6. m_99
7. kotatsugame
8. Ethan_Rao
9. maspy
10. smax

Official participants

1. dengTianliang
2. i_will_be_less_than_blue
3. tlvvpdus
4. PokerCareer
5. casual11
6. wildwolf_ptyzs
7. Puranya_
8. 963noah
9. LovelyEther
10. warner1129

UPD3: Editorial is published.

Hello, Codeforces!

We are happy to invite you to an exciting online event: ICPC 2022 Online Challenge powered by HUAWEI，which will start on September 15, 2022, 00:00 UTC (UTC+0).

In this Challenge, you will have a unique chance:

• to compete for 2 weeks online during the challenge
• to solve 1 or 2 problems prepared by different business domains of HUAWEI
• to win amazing prizes from HUAWEI!

As a special prize, HUAWEI together with ICPC Foundation will provide the travel trip to the 46th Annual ICPC World Finals in a guest role to the 2 winners (1 winner for each problem)!

Everyone is welcome to participate. It is an individual competition. ICPC 2022 Online Challenge powered by HUAWEI (open to the public): September 15 — September 30, 2022, 00:00 UTC (UTC+0)

This time HUAWEI has prepared 2 challenging tasks for you from different business domains – Data Communication and Cloud.

You are free to choose which problem you would like to solve, and you are also welcome to solve both problems, but please remember the total runtime of both rounds, which start simultaneously, is 15 days only. We hope you'll enjoy this complex yet very exciting Challenge!

Each problem will have its own scoreboard and its own prize fund, so this is a unique chance for you to win double prizes for two solved problems!

Problem No 1: Optimal graph partitioning for fast routing

This problem comes from HUAWEI’s Data Communication business domain, in which routing algorithms have always been a critical issue. In the future, as more and more communication devices are connected to networks, data communication will face an interconnected network formed by ultra-large-scale network devices.

In this challenge, data communication experts of HUAWEI will provide you several network topologies. By dividing them into abstract domains, you need to scale down these topologies and enable quick route calculation, so that fast route convergence can be implemented on large-scale networks. Domain division must address the optimal routing and network scale constraints, so a routing algorithm that effectively divides domains while also meeting these constraints is the core of the algorithm design.

Problem No 2: Topology-Aware VM Placement

This problem comes from another HUAWEI’s business domain – Huawei Cloud. To win the competition in cloud computing market, major cloud service providers are focusing on improving the utilization of cloud resources, as this will allow to reduce the cost of cloud services. It is estimated that even a 1% increase in cloud service resource utilization can save millions of dollars in costs. The optimization of resource utilization, in turn, requires the development of advanced algorithms and technologies for cloud resource management.

The virtual machine (VM) placement algorithm considered in this contest is one of these critical algorithms, which is used to select a physical machine for running a user VM. Since VM requests arrive dynamically, this algorithm works in online fashion. The main goal is to maximize the number of successfully placed VMs. As the algorithm runs on a resource pool of fixed size the more requests are allocated, the less resources are wasted and the more resource efficient is the algorithm. A secondary goal is to maximize the number of VMs placed without violation of additional soft constraints, as it improves the cloud user experience.

Prizes

Grand Prize (Rank 1):
Problem 1: 15,000 EUR + the travel trip to the 46th Annual ICPC World Finals in a guest role
Problem 2: 15,000 EUR + the travel trip to the 46th Annual ICPC World Finals in a guest role

First Prize (Rank 2- 6):
Problem 1: 8,000 EUR
Problem 2: 8,000 EUR

Second Prize (Rank 7- 16):
Problem 1: 3,000 EUR
Problem 2: 3,000 EUR

Third Prize (Rank 17 – 46):
Problem 1: HUAWEI FreeBuds
Problem 2: HUAWEI FreeBuds

* If the allocated HUAWEI Challenge prize cannot be delivered to your region for any reason it may be replaced by another prize of the same value (if no legal restrictions), at the discretion of the sponsor.

Challenge Rules and Conditions

By participating in this Challenge, you agree to the Challenge Rules and Conditions of Participation

Good luck, we hope this will be fun!

Hello! Codeforces Round #820 (Div. 3) will start at Sep/12/2022 17:35 (Moscow time). You will be offered 6-8 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have a rating of 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks.

You will be given 6-8 problems and 2 hours and 15 minutes to solve them. One of the problems in this round is interactive. Don't forget to read the guide on interactive problems.

Note that the penalty for the wrong submission in this round is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participant of the third division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them)
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of our work. Problems have been created and written by ITMO University team: MikeMirzayanov, myav, Gol_D, Aris, Gornak40, SixtyWithoutExam and Vladosiya.

We would like to thank: Kniaz, BledDest, Svyat, Be_dos, Timur2006, FelixDzerzhinsky, alphabet321, FedShat, vsinitsynav, Jostic11, HamletPetrosyan, _Roma_, KKT_89, ABalobanov, lightseba, powergee101, DafuQ_o and AshrafEzz for testing the contest and valuable feedback. List of testers will be updated.

Good luck!

UPD 1:

We are in the middle of the round (and missing Gornak40 and Gol_D).

UPD 2: Editorial