Hello Codeforces!

The sixth round of the Kotlin Heroes series recently finished! All the rounds are available to be used for practice here: Episode 1, Episode 2, Episode 3, Episode 4, Episode 5: ICPC Round and Episode 6). Thanks to everyone who participated – you inspire us to work even harder on the problems for the next round, and we think you’re really going to like them!

Congratulations to the top three contestants:

1. tourist
2. Egor
3. Tlatoani

A Kotlin Heroes t-shirt and exclusive Kotlin stickers will be presented to:

1. tourist
2. Egor
3. Tlatoani
4. eatmore
5. uwi
6. Benq
7. Geothermal
8. TadijaSebez
9. JettyOller
10. Maksim1744
11. pashka
12. Sugar_fan
13. dalt
14. galen_colin
15. tabr
16. SYury
17. natsugiri
18. Golovanov399
19. Spheniscine
20. taran_1407
21. Ra16bit
22. Aidos
23. yudedako
24. nuip
25. knightL
26. golikovnik
27. wifiiii
28. Fortin
29. majk
30. WiwiHo
31. Bench0310
32. wu_qing
33. Kuyan
34. Nikitosh
35. cjtoribio
36. receed
37. vadimmm
38. SecondThread
39. LeoPro
40. rapira
41. -14
42. nhho
43. PavelKunyavskiy
44. abc864197532
45. tatyam
46. Heart_Blue
47. Ji_Kuai
48. darnley
49. Potassium
50. 353cerega

These participants also won branded t-shirts:

1. polingram
2. Prateek
3. rotavirus
4. linjek
5. pr3pony
6. ostroumov
7. harshrajani460
8. xiaowuc1
9. arvindf232
10. illyakr
11. Jetman
12. Leksiq
13. IceKnight1093
14. procrastinate7
15. man.yasakov
16. Viktor36
17. matvey.kazakov
18. cmplx-xyttmt
19. SourabhYelluru
20. daisy_2000
21. stanm
22. cristian1997
23. SerVB
24. aaronsms
25. chick_magnet
26. Ditmarscehen
27. My_password_is_qwerty123
28. Misha_Help
29. sohsoh
30. igla
31. ans_human
32. mystic777
33. __RANI
34. CM_when
35. MissNick
36. MrArpit
37. penad
38. XAXAEBATb
39. son8bon
40. RandYan
41. adimiclaus15
42. babkabass
43. KKT_89
44. nishuz
45. BMking
46. KEKWait
47. Kerpoo
48. pineapple_pasta
49. GlobalElite
50. aka2910

We will contact the winners soon to coordinate the delivery of your prizes!

Special thanks goes to SecondThread for streaming the solutions of the entire practice round. Check out this wonderful tutorial: https://codeforces.net/stream/203

If you are still new to Kotlin but want to give it your all in the next round, take a look at Basic Kotlin (solve Koans), Kotlin Playground, this tutorial, and these videos on competitive programming in Kotlin.

We wish you all the best and hope you enjoy coding with Kotlin!

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.

Hello Codeforces!

On Mar/18/2021 17:50 (Moscow time) Educational Codeforces Round 106 (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 Roman Roms Glazov, 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:

Dear Codeforces!

We are coming with another scholarship opportunity to share with you. This time, our scholarship is targeted towards the brightest women in the community.

As you might know, March is the month where the whole world celebrates women. At Harbour.Space we want to use this opportunity to encourage more women to join the tech world and challenge the gender-bias in this field.

We believe that gender equality in the workplace starts with gender equality in the classroom. For that reason, we are offering our Women in Tech Scholarship. The scholarship consists of:

• 50% off the yearly tuition fee: covers around €29,000 for bachelors and €11,450 for masters.
• 32% off the application fee: €85 instead of €125

You can find more information about the scholarship here.

Make sure to apply before March 31st to benefit from the scholarship and discount.

Don’t hesitate to share this opportunity with any bright women in your personal circle as well. A simple share can help us transform someone's life.

We are always happy to see Codeforce members join the Harbour.Space family.

Keep in touch and follow us on LinkedIn for more scholarship opportunities. And follow us on Instagram to stay in touch with our student life, events, and success stories from our students.

Good luck on your round, and see you next time!

Harbour.Space University

Congratulations to the winners:

149 successful hacks and 1485 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

UPD: Editorial is out

Hello again, Codeforces!

Artyom123 and I are happy to invite you to Codeforces Round 708 (Div. 2), which will take place on Mar/17/2021 17:35 (Moscow time). This round will be rated for the participants with rating lower than 2100

These are some awesome people that we would like to thank:

• isaf27 for round coordination and helpful ideas
• physics0523, Kotehok3, Ziware, Kirill22, Absyarka, AliShahali1382, notTehlka, Mohammad_Yasser, FairyWinx, kassutta, LazyPrime, kalki411 for testing and providing feedback
• MikeMirzayanov for beloved platforms Codeforces and Polygon.

You will have 2 hours to solve 5 problems (and 2 subtasks). This time the statements are not related to Valorant, but we still play it sometimes.

We hope that you will like all problems and you won't face any troubles during the contest. Good luck!

The scoring distribution: 500 — 750 — (750 + 500) — 1750 — (1500 + 1500)

UPD: Editorial

Hello, Codeforces!

I understand that 2021 has been going on for a long time, but here I have picked up a subset of some of the improvements that the Codeforces team made in 2020. Soon I will publish numbers (no, charts) with statistics for 2020. In the meantime, I bring to your attention a list of changes and improvements.

By the way, this is a decent list. This is about half to a quarter of all changes. It's just that other changes are more often somewhere in the internals of the system and are not visible to users. Please read this list. Each item is the effort of someone from the team. Thanks to geranazavr555, kuviman and cannor147 for their efforts. You've made our platform better! Well, by the way, I don't quit programming and many improvements were made by me.

The items on the list are written in a concise and informal form, many of the items I just copied from commit messages from git. If you want more details — ask in the comments, we will tell you! Of course, I forgot to include some improvements in the list.

Hello!

Right now happens the first tour of the Open Olympiad in Informatics, and tomorrow will be the second one. This contest is prepared by Moscow Olympiad Scientific Committee that you may know by Moscow Team Olympiad, Moscow Olympiad for Young Students and Metropolises Olympiad (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541, 545, 567, 583, 594, 622, 626, 657, 680, 704).

Open Olympiad consists of the most interesting and hard problems that are proposed by a wide community of authors, so we decided to conduct a Codeforces regular round based on it, which will happen on Mar/13/2021 12:05 (Moscow time) and will be based on both days of the Olympiad. Each division will have 6 problems and 2 and a half hours to solve them.

We kindly ask all the community members that are going to participate in the competition to show sportsmanship by not trying to cheat in any manner, in particular, by trying to figure out problem statements from the onsite participants. If you end up knowing some of the problems of Moscow Open Olympiad (by participating in it, from some of the onsite contestants or in any other way), please do not participate in the round. We also ask onsite contestants to not discuss problems in public. Failure to comply with any of the rules above may result in a disqualification.

Problems of this competition were prepared by Akulyat, KiKoS, wrg0ababd, budalnik, blyat, alexX512 isaf27, ismagilov.code, DebNatkh, Siberian, NiceClock guided by cdkrot, vintage_Vlad_Makeev, GlebsHP, Zlobober, meshanya, ch_egor, grphil, voidmax, Endagorion and Helen Andreeva.

Thanks to adedalic and KAN for the round coordination, statement translation and preparation of problems for the second division, and also thanks for MikeMirzayanov for systems Codeforces and Polygon, which was used to prepare problems of this olympiad.

Also thanks to 4qqqq and Aleks5d for providing an additional problems that helped to create (I hope) a balanced problem set for the round, and Um_nik for testing!

Good luck everybody!

Due to the official competition source codes of other participants will not be available for an hour after the end of the round.

UPD1:

Please do not discuss problems publicly until 12:30 UTC.

The scoring distribution for both divisions is not standard:

• div1: 750 — 750 — 1500 — 2000 — 2500 — 3000
• div2: 500 — 1000 — 1750 — 1750 — 2500 — 3000

UPD2: Editorial

UPD3: Winners!

Div. 1:

1. tourist
2. jiangly
3. maroonrk
4. ecnerwala
5. Rewinding

Div. 2:

1. 20I6wudi
2. ShimaRin
3. fengqiyuka
4. gezlik
5. b___

Hello, Codeforces!

Daniel_yuan, waaitg, smg23333 and I are glad to invite you to Codeforces Round 706 (Div. 1) and Codeforces Round 706 (Div. 2), which will take place on Mar/10/2021 15:05 (Moscow time). Note the unusual time of the round. In both divisions, you will be given 6 problems and 2 hours to solve them all.

We would like to thank:

• isaf27 for the great coordination and discussion.
• KAN for the great help with round preparation.
• Wolam for all his rejected problems and discussing the problems with us.
• tiger0132, EmptySoulist, CYJian, parallelist, Sunward_z and ODT for testing the problems in advance and sharing their ideas.
• dXqwq, LTb, rui_er, CSP_Sept, Qiulyqwq, mac, dapingguo8, mazihang2022, Ashishgup, aajisaka, i_wyxkk_ak, mnaeraxr, Mitsukasa_Ayase, Oak_limy, Iidaqi, zscoder, Lovely_Ran, lgswdn, feecIe6418, orzdevinwang, happydef, Kewth, Widowmaker, star_xingchen_c, 3.141592653, Aaeria and 4c5948 for testing the round and their invaluable feedbacks.
• MikeMirzayanov for amazing platform Codeforces and Polygon.

Score distribution will be announced before the round.

Hope you all gain positive ratings $$$\Delta$$$ in this round!

UPD1: Score distribution is

Div. 2: $$$500-1000-1500-2000-2500-3000$$$

Div. 1: $$$500-1000-1500-2000-2500-3250$$$

UPD2: Editorial

UPD3: Congratulations to the winners:

Div 1:

1. Radewoosh
2. maroonrk
3. tourist
4. Um_nik
5. Egor

Div 2:

1. shikaichengwoerzi
2. grey
3. csyakuoi
4. sh_mug
5. notTehlka

Hello, Codeforces!

First and foremost, we would like to say a massive thank you to everyone who entered and submitted their answers to the five Kotlin Heroes competitions which were held previously: Episode 1, Episode 2, Episode 3, Episode 4, and Episode 5: ICPC Round.

Ready to challenge yourself to do better? The Kotlin Heroes: Episode 6 competition will be hosted on the Codeforces platform on Mar/09/2021 17:35 (Moscow time). The contest will last 2 hours 30 minutes and will feature a set of problems from simple ones, designed to be solvable by anyone, to hard ones, to make it interesting for seasoned competitive programmers.

Prizes:

Top three winners will get prizes of $512, $256, and $128 respectively, top 50 will win a Kotlin Heroes t-shirt and an exclusive Kotlin sticker, competitors solving at least one problem will enter into a draw for one of 50 Kotlin Heroes t-shirts.

Registration is already open and available via the link. It will be available until the end of the round.

The round will again be held in accordance with a set of slightly modified ICPC rules:

• The round is unrated.
• The contest will have 9 problems of various levels of complexity.
• You are only allowed to use Kotlin to solve these problems.
• Participants are ranked according to the number of correctly solved problems. Ties are resolved based on the lowest total penalty time for all problems, which is computed as follows. For each solved problem, a penalty is set to the submission time of that problem (the time since the start of the contest). An extra penalty of 10 minutes is added for each failed submission on solved problems (i. e., if you never solve the problem, you will not be penalized for trying that problem). If two participants solved the same number of problems and scored the same penalty, then those of them who had previously made the last successful submission will be given an advantage in the distribution of prizes and gifts.

If you are still new to Kotlin we have prepared a tutorial on competitive programming in Kotlin and Kotlin Heroes: Practice 6, where you can try to solve a few simple problems in Kotlin. The practice round is available by the link.

We wish you luck and hope you enjoy Kotlin.

Hi!

I continue to make videos on algorithms. This time the topic is more basic. In this video, I talk about prefix sums and how they can help you to find sum on segments. You can also learn from this video how to easily generalize prefix sums for 2D, 3D, 4D, etc. cases. In addition, we'll also talk about a simple concept named difference array, which can easily help in some sorts of situations where it seems like you need some complex data structures. And in the end, we'll learn how to add constants, arithmetic progressions, and even quadratic functions to a segment of an array.

Link to the video

The video is in Russian but English subtitles are available. I'd be glad if you watch the video and leave a comment below with your impressions, thoughts, and ideas for future videos. You may also want to text me on telegram if you didn't understand something or you have any questions. I'll be glad to answer!

I'm sorry you need to watch it with subtitles but I'm gonna make an English channel soon. So stay tuned!

If you didn't see it already, I also have a video on disjoint sparse table: here.

Codeforces group with a contest

My realizations:

1D prefix sums

1D prefix sums with structures

2 methods for finding 2D prefix sums: one, two

1D difference array

1D difference array with structures

The future is bulletproof
The aftermath is secondary
It's time to do it now and do it loud!

Hello, Codeforces!

74TrAkToR and I are glad to invite you to our Codeforces Round 705 (Div. 2), which will be held at Mar/06/2021 17:05 (Moscow time). Notice the unusual time of the round. The round will be rated for all the participants with rating strictly less than 2100.

We have already held a round and we have worked on errors:

• the statements will be short and clear
• we tried to make pretests stronger
• the editorial will be published shortly after the round ends

We would like to thank everyone who helped us a lot with round preparation.

• Our coordinator KAN for brilliant coordination of the round.
• Our testers Tlatoani, sava-cska, DIvanCode, BLIZZARD, Mlxa, plagues, voventa, hg333, golions, kassutta for great testing and helpful notes.
• MikeMirzayanov for amazing Codeforces and Polygon platforms.

You will be given 6 problems. You will have 2 hours 15 minutes to solve them.

UPD: Score distribution $$$750-1250-1750-2250-2750-3250$$$.

UPD2: Editorial

UPD3: Congratulations to the winners!

Div. 2:

1. sawa855

2. A05

3. DeIeted

4. rainboy

5. scli_kws

Div. 1 + Div. 2:

1. neal

2. BigBag

3. fastmath

4. Sugar_fan

5. tute7627

We wish everyone good luck!