Hi everyone!

I would like to invite you to my fourth Codeforces Round, which I have made with my friends FastestFinger and TheOneYouWant. In terms of problems, it is my favorite among all my rounds.

With that said, I bring to your attention our new Codeforces Round 646 (Div. 2) that will take place on May/31/2020 17:35 (Moscow time). 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:

• FastestFinger and TheOneYouWant for helping with preparing problems and giving new ideas.
• antontrygubO_o for coordinating our round
• 300iq, Jeel_Vaishnav, Ari, aryanc403, mahmoudbadawy, Vivek1998299, Uzumaki_Narutoo, Bakry, smartnj and Nikhil_Medam for testing the problems.
• MikeMirzayanov for Codeforces and Polygon platforms.

You will be given 6 problems and 2 hours to solve them. Scoring distribution will be announced later.

Good luck! :D

UPD: Scoring Distribution: $$$500-1000-1500-2000-2250-3000$$$

UPD2: Editorial (with memes, and detailed explanation) — Hope you guys enjoyed the contest! :D

I hope you guys enjoyed the contest and we hope to host another one soon! The next one will be more balanced :P

With that said, here are the tutorials:

Author: Ashishgup

C++ Code: 51651509

Java Code: 51651164

Author: Ashishgup

C++ Code: 51651887

Java Code: 51651375

Author: Ashishgup

C++ Code: 51652029

Java Code: 51651756

Author: Vivek1998299

C++ Code (Above Logic): 51652491

C++ Code (Mobius Inversion): 51652104

Author: Jeel_Vaishnav

Java Code: 51652167

Author: Jeel_Vaishnav

Java Code: 51652020

Hello everyone!

I would like to invite you to participate in HackerEarth's February Easy '19. The contest will be held on 1st February, 2019 at 21:00 IST

The problems have been prepared by me (Ashishgup) and Jeel_Vaishnav. We would like to thank TooDumbToWin for testing the round and trytolearn for giving us the opportunity to hold the contest.

You will be given 6 algorithmic questions to solve in 3 hours. Partial scoring will be used (you get points for passing each test case). Although the contest is targeted towards beginners, we hope that everyone finds the tasks interesting. The contest is rated for all and prizes will be awarded to the top 3 beginners (i.e. programmers with a rating of 1600 or less before the challenge starts):

• First place: $75 Amazon gift card.
• Second place: $50 Amazon gift card.
• Third place: $25 Amazon gift card.

Good luck and have fun!

UPD: The contest begins in 15 minutes.

Creating this blog for discussion of problems/solutions from Indian ICPC Regionals

Onsite Contest Standings:

• ICPC Asia-Kharagpur Onsite Contest 2018
• ICPC Asia: Gwalior-Pune Onsite Contest 2018
• ICPC Asia: Kolkata-Kanpur Onsite Contest 2018

Online Replay Contests:

• ICPC Asia-Kharagpur Onsite Replay Contest 2018
• ICPC Asia: Gwalior-Pune Onsite Replay Contest 2018
• ICPC Asia: Kolkata-Kanpur Onsite Replay Contest 2018

There is also the whole issue with test cases in the regionals so far:

Gwalior-Pune:

• "Flipping Polygons" had wrong TCs which affected a few teams, with 3 of them getting AC later. Converting WA -> AC after contest is alright, but the time wasted by teams in trying to correct their codes could have been utilized in solving a different question.
• "Three Strings" had really weak TCs, considering that solutions taking max prefix and max suffix only get AC as well. (Breaking test case: 1 abc cde bcde)

Kolkata-Kanpur:

• "Chef and Alien Invasion" again had wrong TCs, and teams were affected, with even the teams qualifying for World Finals changing places. ACs were converted to WAs after the contest (although that doesn't affect the ranks), not to mention that it was announced that the problemset for the regional was made 1 day before the contest, which is not what is expected of an ICPC regional.

Hi everyone!

I would like to invite you to my second Codeforces Round, which I have made with my friend and Snackdown partner Jeel_Vaishnav.

With that said, I bring to your attention our new Codeforces Round 523 (Div. 2) that will take place on Nov/22/2018 18:45 (Moscow time). 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 Jeel_Vaishnav for his help with preparing problems, cdkrot for coordinating our round and Um_nik, vintage_Vlad_Makeev, Aleks5d, KeyurJain & Mahir83 for testing the problems. I would also like to thank MikeMirzayanov for Codeforces and Polygon platforms.

You will be given 6 problems and 2 hours to solve them. Scoring distribution will be announced later.

Link to My Coding Library for those interested :)

Good luck! :D

UPD: Scoring Distribution: 500-1000-1500-2000-2500-2750

UPD2: Editorial

There are many useful websites that extract data from Codeforces and give some statistics, problem recommendations, graphs, etc.

I thought that collecting them all in one place would be a good idea. Please comment the websites you find useful :D

List as of now:

• CF-Predictor (Original Blog): Predicts the expected rating change during and after contests.

• Code-Drills (Original Blog): Recommends problems for a list of user & gives statistics on total number of problems solved.

• Codeforces Visualizer (Original Blog): Gives various statistics for a user, and supports comparison between two users.

• CF Statistics (Original Blog): Comparison between 2 users gives the unique problem-set and the shared problem-set solved by the users.

• Codeforced: Gives a contest-wise result of which questions have been solved and which haven't been solved (but attempted). Essentially, a complete list of "unsolved problems" as opposed to Codeforces' last 15 unsolved.

• Virtual Contest Picker (Original Blog): Given a set of usernames, finds contests where none of the users have made any submissions.

• Codeforces Comment/Blog Statistics (Original Blog): Gives statistics per user: No of blogs/comments/upvotes.

• Team Dashboard (Original Blog)

• Codeforces Practice Tracker (Original Blog)

• Codeforces Upsolving Helper (Original Blog): Returns list of all attempted problems for a user that don't have AC.

• CF Notifications (Original Blog): Notifies the user of their verdict on any CF submission.

Some missing sites:

• Most popular users

Due to my dislike of CodeChef discuss, I choose to discuss/rant about this topic here on Codeforces. Although non-Indian participants may not relate to the ICPC situation, I'm sure the CookOffs and Lunchtimes are a common issue.

First of all, why is the difficulty gradient so fucked up every single time? (Contest Link). Be it ICPC, or CookOffs, or LunchTimes, the same thing is seen over and over again.

Scoreboard for reference:

Secondly, why does online ICPC selection have only 5 questions for 3 hours? Not to mention, 3 of them are pretty hard, and the difficulty drop is huge, so it does not help filter out deserving teams from undeserving ones.

Is ICPC selection supposed to be based on a speed typing test? In unbalanced contests like this, it almost always happens that some undeserving teams qualify. Every penalty matters a lot too. For instance, we failed to qualify for one of the regionals — KGP — because of 1 penalty.

So, my question to CodeChef is: How hard is it to set a balanced contest? Codeforces seems to does it every week. CodeChef fails to do it even in its most important yearly contest, along with its monthly short contests, every single time.

I honestly believe that even I can set a better contest than this. Lastly, why was the leaderboard hidden as soon as the contest ended?

(PS: Teammate's rage after contest: Pic1, Pic2 )

I have been trying to cover a lot of commonly used Algorithms/Data Structures and maintain neatly written codes at my repository (since most codes are not neatly written in Competitive Programming in general, and I prefer neatly written codes):

https://github.com/Ashishgup1/Competitive-Coding/

Most of the codes are taken from various sources and already existing Coding Libraries, and many Algorithms/Data Structures are missing which I plan to add soon.

Hope you enjoy and feel free to point out any bugs you notice :)

I hope you guys enjoyed the contest — I hope to host another one soon :D

With that said, here are the tutorials:

Author's Code: 42591712

Author's Code: 42591830

Author's Code: 42591846

Author's Code: 42591882

Author's Code: 42592019

Author's Code: 42592026

Tester(cdkrot)'s Code: 42593206

For O(n³) or O(n²) solution, refer to this comment by pranjal.ssh

Hi everyone!

It has been almost 2 years since I joined Codeforces, and it has been a great journey as a contestant. I now try to take a shot at problem-setting with my friend Mahir83.

With that said, I bring to your attention my new Codeforces Round 508 (Div. 2) that will take place on Sep/06/2018 18:35 (Moscow time). If your rating is less than 2100, this round will be rated for you; otherwise, you can participate out of competition.

I would like to thank Mahir83 for his help with preparing problems, cdkrot & 300iq for coordinating my round and Um_nik, craborac, vintage_Vlad_Makeev, vovuh & BledDest for testing my problems. I would also like to thank MikeMirzayanov for Codeforces and Polygon platforms.

You will be given 6 problems and 2 hours to solve them. Scoring distribution will be announced later.

Good luck!

UPD: Scoring Distribution: 500-1000-1500-1750-2250-2750

UPD2: Editorial

Official announcement here

As per the announcement, the online rounds will start in October 2018 and the onsite finals will be held in February 2019.

These days, cases of cheating (reported or otherwise) go un-handled as can be seen from this blog. However, this is a cheating case that needs to be handled separately, so it is still somewhat understandable

But what about:

1) This case where the code is literally copy-pasted letter to letter with the difference being 2 spaces in the entire code?

2) These two submissions from yesterday's contest: 40441960 and 40428475 where there is not even a single character difference. Their codes for C are copied too, albeit with some modification of spaces.

In both of those cases, no-one was disqualified and I'm sure there must be more such cases.

Can we have some way of reporting these cheating cases that are then handled (rather than commenting on blogs or creating new blogs) and a better plagiarism checker?

Trying to open the Announcement Blogs or Tutorials of some of the past contests (such as: http://mirror.codeforces.com/contest/877) gives "Access Denied". What is the reason behind this? Is it a bug?

In the "Contests" tab, the change along the border of 2100 is shown as "became Candidate Master" both ways. I guess this should either be updated with the current rating system or be removed altogether (if the system only wants to reflect rating system changes from when it was introduced), because right now it is just weird.

CodeForces seems to have finally introduced a button for copying the sample input on the problem pages :D

Official announcement blog here

I love the revamped look of the site and the new rating system which is pretty similar to CodeForces and TopCoder. I also like that they combined the ratings of Long Contests (Challenges) and Short Contests (Cook-offs and Lunchtimes) to form an overall rating and rank, while also maintaining separate ranks (country and global) for each of them.

I have noticed that quite a few people changed their username on CodeForces, but I can't figure out some of their original/previous usernames because of bad memory/changed profile picture accompanied with the changed name. Is there any method to do so?