By 300iq, 6 years ago, translation, In English

Hi!

At Apr/06/2019 14:35 (Moscow time) we will host Codeforces Global Round 2.

It is the second round of a new series of Codeforces Global Rounds supported by XTX Markets. 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: 300iq, cyand1317, Aleks5d, RDDCCD, KAN, gen.

Thanks KAN for his help in the round's coordination, and also isaf27, Lewin, ----------, Errichto, arsijo, cdkrot for testing the round!

Удачи!

Congratulations the winners!

1) ecnerwala

2) tourist

3) Um_nik

4) Endagorion

5) Petr

Editorial.

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Announcement of Codeforces Global Round 2
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By MikeMirzayanov, 6 years ago, In English

ICPC World Finals 2019 will begin on April 4, 2019 at 11:00 (UTC). This event is the main event of the year in the world of sports programming!

In the past 20 years alone, ICPC participation has increased by more than 2000%. The contest evolved into its present form as a multi-tier competition in 1977, with the first finals held in conjunction with the ACM Computer Science Conference. Last year, ICPC Regional participation included 52,709 of the finest students and faculty in computing disciplines from 3,233 universities in 110 countries. We remind you that in the current world champion is the team of Moscow State University.

Codeforces wishes the teams to show a vivid and interesting contest. We wish to find beautiful solutions, write without bugs and enjoy many accepted problems!

Links:

ICPC World Finals 2019 English Broadcast:
Legends Live Stream (Endagorion + Petr + tourist):

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By scott_wu, history, 6 years ago, In English

Hey all!

We'll be running ICPC Connections this year at World Finals! ICPC Connections is powered by Lunchclub and is a way for contestants, coaches, and alums at World Finals to get to meet one another. We first ran Lunchclub at ICPC last year (thanks M.Mahdi for the shoutout!) and are excited to be back.

If you're in Porto this week and would be interested to meet fellow attendees, sign up at lunchclub.ai/icpc! And if you're curious to learn more about what we're working on, check out our main product here :)

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By Nickolas, 6 years ago, translation, In English

The contest is over; I hope at least some of you enjoyed it :-) The editorial is published here.


The 7th April Fools Day Contest will take place on Monday April 1st. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces. To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018.

As usual, to enjoy competing in this round you'll need a sense of humor compatible with mine. Good luck, and have fun!

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By vovuh, 6 years ago, translation, In English

Hello! Hope you missed me :) As far as some people say, because of copy-pasted announcement this round wouldn't be interesting. But the real thing is that I'm very sick now and I'm very glad that I prepared this round at all. Hope you will enjoy it. Good luck to all!

<copy-pasted-part>

Hello! Codeforces Round 550 (Div. 3) will start at Mar/31/2019 17:05 (Moscow time). You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 or 7 (or 8) problems and 2 hours to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) 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 participants of the third division, you must:

  • take part in at least two 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 my work. Thanks to my good friends Mikhail awoo Piklyaev, Maksim Neon Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

I also would like to say that participants who will submit wrong solutions on purpose and hack them afterwards (example) will not be shown in the hacking leaders table.

</copy-pasted-part>

UPD: Editorial is published!

UPD2:

Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 WNSGB 7 206
2 kaixinqi 7 335
3 _sys 6 188
4 Moririn2528 6 206
5 CarusoX 6 212

Congratulations to the best hackers:

Rank Competitor Hack Count
1 wanderer163 21
2 tokitsukaze 14
3 Fe4RLess 6
4 smit.mangukiya 4
5 chandak_vikas 4
93 successful hacks and 132 unsuccessful hacks were made in total!

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

Problem Competitor Penalty
A anurag918273 0:02
B probIem-solving 0:07
C Shuba_realniy_krasav4ik 0:05
D vnquynh_hac_am 0:12
E probIem-solving 0:28
F ForeverFire 0:16
G IZONE 0:20

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By grphil, 6 years ago, translation, In English

Hi Codeforces!

I'm glad to invite you to Codeforces Round 549 (Div. 1) and Codeforces Round 549 (Div. 2), which will be held on Mar/30/2019 20:10 (Moscow time). The round will be rated for both divisions.

Problems were prepared by me, Vladimir vekarpov Karpov, Daniil qoo2p5 Nikolenko, Askhat super_azbuka Sakhabiev and Mike MikeMirzayanov Mirzayanov.

Thanks to KAN and arsijo for helping us, and MikeMirzayanov for the great Codeforces and Polygon platforms.

UPD: You will be given 6 problems in the second division, 5 problems in first division and 2 hours to solve them.

Good luck and Have fun!

The scoring distribution will be announced later.

UPD1: Top 12 participants of div1 round, who are ICPC world finalists, will get branded Codeforces hats. Further details are here.

UPD2: The score distribution is 500-1000-1000-1500-2000-2500 for the second division and 500-1000-1500-2000-2500 for the first division.

List of the winners of the contest:

Div1

  1. Um_nik

  2. LaiMeiyun

  3. Benq

  4. dotorya

  5. ilyakor

Div2

  1. Infleaking

  2. lamejeck

  3. ZeroTwo

  4. Amtek

  5. 2qbingxuan

UPD3: Sorry for the delay, the editorial is available here

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By Um_nik, history, 6 years ago, In English

Last three blogs on main page of CF shouldn't be on main page. And it become quite common thing in recent CF practice. Main page should contain only something that all users should see. Of course, round announcements, platform upgrades and sponsor posts should be on main. Blogewoosh had some rights to be on main because it was cool series of blogs which had chosen CF as its platform so CF should have praise it (but it would be nothing wrong for it to be just in Radewoosh's posts like everything else). But all other stuff? Let's look at some examples for the last year.

Important: I'm not saying that these blogs are bad. Most of them are good. But why are they on main page? CF have great blogs system, every user can write something helpful. Just don't put random stuff on main.

Some algorithm stuff which is better than other algorithm stuff, I guess:
C++ STL: Order of magnitude faster hash tables with Policy Based Data Structures
Linear Recurrence and Berlekamp-Massey Algorithm
[Tutorial] Searching Binary Indexed Tree in O(log(N)) using Binary Lifting
Don't use rand(): a guide to random number generators in C++ — this one is kinda mandatory for participating in CF rounds due to bad compilers on CF, so it is good that it was on main
Blowing up unordered_map, and how to stop getting hacked on it

Random contests in gym which are better than other contests in gym, I guess:
Original Gym contest: Geometry Special 2018
2018-2019 ACM-ICPC, Asia Xuzhou Regional Contest (Online Mirror on Gym)
ROI 2018 in GYM

Promoting Errichto, I guess:
Stream
Sums and Expected Value — part 1
Lecture #3 — Exchange arguments (sorting with dp)

More sponsored stuff??
Анонс кружков от tinkoff.ru
My Course at Harbour.Space University: Advanced Algorithms and Data Structures (January, 2019) — selfpromotion, also nobody should pay 1000 euro for a course no matter what this course is. This is just abusing position as Codeforces CEO

IDK
Lunch Club at ICPC WF
The D programming language in competitive programming
Codeforces Contests Picker Goes Live: Celebrating ICPC Season
Team dashboard
Let's bring souvenirs to the ICPC World Finals
Unnecessary blogs on main

MikeMirzayanov's personal blog:
Hello, ITMO! — yes, there are some inforamtion about platform improvements but it is just an excuse to write this post
Codeforces Round #547 (Div. 3) — round announcement? Um_nik is totally crazy. Well, yes, but the photo and "I'm so cool I made a round in 6 hours" is nonsense. Also how about wait in line for half a year like others do?

It looks like it is just a question of whether Mike saw and liked the post. MikeMirzayanov, CF main page is not your personal blog. Please don't use it as your favorite tab.

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By M.Mahdi, history, 6 years ago, In English

Hi everyone!

On-site competitive programming competitions are rare and valuable events, and we all practice hard to have great competition. But I guess we are missing a point. One notable opportunity that exists in these kinds of events is getting to know other members of the competitive programming community, more than what we see in the scoreboards. The lunch club was a cool way of using this opportunity. (scott_wu, are we going to have the club this year? )

I remember the last day of IOI 2017. After everything was finished and the medals were given, I went back to the hotel and I saw an unexpected scene. I found there is this cool tradition in IOIs that in the last day contestants gather together, take pictures, and give out souvenirs. (FYI, I wasn't an IOI participant, I was in the host scientific committee.) I still have the souvenirs that I got from Japanese and Chinese contestants, and It encouraged me to search and get more familiar with their cool cultures.

So, in the remaining days before the trip to Portugal, I'm going to buy some souvenirs to give out in the world finals. I guess we can do this after dinner on the last day, in the lobby of the hotel. I'd be glad if you come and get it!

If you are interested, join the club and bring something from your country for everyone! Maybe this way, we start the tradition of bringing souvenirs to the world finals.

UPD: As stated here, the meeting is better to be in the farewell dinner hall instead of the hotel lobby. So we'll meet in Alfândega — West Ground Floor on Thursday. We will need to bring our souvenirs when leaving the hotel in the morning because we will go directly to the closing ceremony and celebration dinner from the contest. Please let your friends know the change so that no one misses the gathering.

UPD2: Don't forget your souvenirs tomorrow!

Good luck in the contest. :)

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By Errichto, 6 years ago, In English

Hi.

On Wednesday at 9:05 CET / 8:05 UCT you can participate in the GYM version of the finals of 2017-2018 Russian Olympiad in Informatics (ROI), Day 1. And on Thursday there will be day 2, same time.

Links to GYM contets: day1 and day2.

5 hours, 4 problems, IOI-style scoring with subtasks. Statements will be available in three languages: English, Russian, Polish.

We wanted to use those problems in a camp in Warsaw so we had to import the problems to some system anyway. Then why not Polygon+Codeforces and thus allowing everybody to participate? Huge thanks to MikeMirzayanov for helping me with using GYM.

And credits to problem authors: Andreikkaa for Radium, Endagorion for Viruses, pashka for Innophone, Георгий Корнеев and GlebsHP for Quantum Teleportation.

Second day authors: cdkrot for Decryption, "jury" for Quick Sort, GlebsHP for Robomarathon, Endagorion for Addition without carry.

I will post a very short editorial in English here, after the contest.

Extraction of radium
Innophone
Quantum teleportation
Viruses

Second day tomorrow, same time.

Thank you for participation.

Addition without carry
Decryption
Quick sort
Robomarathon

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By MikeMirzayanov, 6 years ago, translation, In English

Hi Codeforces!

Here are some recent improvements here and in Polygon.

Weak and Leaked Passwords

We often hear about password leaks from various services. Considering that having common passwords is a common (but insecure) practice, we've improved Codeforces and Polygon to identify weak or leaked passwords. If on the top of the website you see a message that your password is not secure, then just change it immediately.

Type of the round when creating a contest proposal

This item improves our work with the writers. When creating a contest proposal, please indicate the type of a round. Leave the field empty only if you don't know the type of the round (it is strange).

Calendar

We've fixed errors when synchronizing official Codeforces rounds with the calendar. Now everything should be correct.

I trust this user

Currently, Codeforces provides a mature infrastructure for organizing contests, olympiads and trainings. With the help of domain groups and mashups, competitions of various levels were hosted on Codeforces. The organizers are sometimes not regular users of Codeforces rounds and do not have rights to some of the actions. Now, any red user can confirm his trust in another account, and he will get the right to: write comments/posts, create private groups, create mashups. I hope this will save me from a certain routine of processing such requests.

Confirmation via email when entering Polygon

When you sign in Polygon, your IP-address and browser will be verified. If you didn't use them in the recent past, then you may be asked to sign in with a confirmation email. In this case, just follow the secret link that comes to your email.

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