We invite you to participate in CodeChef’s Starters 193, this Wednesday, 2nd July, rated for all users.

Time: 8:00 PM — 10:30 PM IST

Joining us on the problem setting panel are:

• Setters: Dominater069, IceKnight1093, sheercold and Codula

• Admin: Dominater069

• Tester: SmolBrain

• Editorialist: IceKnight1093

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Note: The problems are based off the Indian IOI Training Camp 2025. As such, there might be more unusual problems, and more subtasks. If you have participated in the camp, or know the problems in some other way, please do not participate.

Congratulations to Top 5 in Div1!

• Rank $$$1$$$ : jeroenodb
• Rank $$$2$$$ : EnofTaiPeople
• Rank $$$3$$$ : Nachia
• Rank $$$4$$$ : kotatsugame
• Rank $$$5$$$ : PCTprobability

We invite you to participate in CodeChef’s Starters 191, this Wednesday, 18th June, rated for 6 stars (i.e. for users with rating < 2500).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin: Shreyan Dominater069 Ray

• Statement Verifier and Tester: Sushil SmolBrain Raaja.

• Text Editorialist : Nishank IceKnight1093 Suresh.

• Setters: Shreyan Dominater069 Ray, Sushil SmolBrain Raaja.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

We invite you to participate in CodeChef’s Starters 189, this Wednesday, 4th June, rated for 5 star (i.e. for users with rating < 2200).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin and Statement Verifier: Shreyan Dominater069 Ray

• Text Editorialist: Nishank IceKnight1093 Suresh.

• Tester: Sushil SmolBrain Raaja.

• Setters: Shreyan Dominater069 Ray, beaten_by_ai.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Congratulations to Top $$$5$$$ in Div $$$1$$$:

• Rank $$$1$$$ : potato167

• Rank $$$2$$$ : TKT_YI

• Rank $$$3$$$ : hint908

• Rank $$$4$$$ : Kude

• Rank $$$5$$$ : Daylight_pro

We invite you to participate in CodeChef’s Starters 188, this Wednesday, 28th May, rated for 6 stars (i.e. for users with rating < 2500).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin and Statement Verifier: Shreyan Dominater069 Ray

• Text Editorialist : Nishank IceKnight1093 Suresh.

• Tester: Sushil SmolBrain Raaja.

• Setters: Shreyan Dominater069 Ray, Matthew chromate00 Roh.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Congratulations to Top $$$5$$$ in Div $$$1$$$:

• Rank $$$1$$$ : potato167
• Rank $$$2$$$ : flytime
• Rank $$$3$$$ : owll
• Rank $$$4$$$ : loki_x
• Rank $$$5$$$ : Nachia

We invite you to participate in CodeChef’s Starters 186, this Wednesday, 14th May, rated for 6 stars (i.e. for users with rating < 2500).

Time: 8:00 PM — 10:30 PM IST

Joining us on the problem setting panel are:

• Contest Admin , Statement Verifier: Shreyan Dominater069 Ray.

• Text Editorialist : Nishank IceKnight1093 Suresh.

• Tester: Sushil SmolBrain Raaja.

• Setters: chromate00, Shreyan Dominater069 Ray, BitWizz.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Here is the breakup of problems division wise:

• Division $$$1$$$ : $$$6$$$ problems.
• Division $$$2$$$ : $$$6$$$ problems.
• Division $$$3$$$ : $$$7$$$ problems.
• Division $$$4$$$ : $$$8$$$ problems.

Congratulations to the Top $$$5$$$ in Division $$$1$$$:

• Rank $$$1$$$ : potato167
• Rank $$$2$$$ : Nachia
• Rank $$$3$$$ : TKT_YI
• Rank $$$4$$$ : Kude
• Rank $$$5$$$ : liympanda

We invite you to participate in CodeChef’s Starters 184, this Wednesday, 30th April, rated for 5 stars.

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin : Shreyan Dominater069 Ray.

• Text Editorialist: Nishank IceKnight1093 Suresh.

• Tester: Sushil SmolBrain Raaja.

• Setters: Shreyan Dominater069 Ray.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Hope you enjoyed the contest. Congratulations to Top 5 in Div1!

• Rank $$$1$$$ : potato167 (sub-30 minute AK!)
• Rank $$$2$$$ : arvindf232
• Rank $$$3$$$ : Kude
• Rank $$$4$$$ : noya2
• Rank $$$5$$$ : harurun4635

We invite you to participate in CodeChef’s Starters 183, this Wednesday, 23th April, rated for 6 stars.

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Author : Shreyan Dominater069 Ray.

• Tester: Archit Pols_Agyi_Pols Kumar.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

IOI Bootcamp: Newton School of Technology (NST)

Are you a school student passionate about competitive programming? Join us for an intensive 13-day IOI training camp designed to nurture India’s future programming champions.

Why Join?

Get exposure to university-level CS knowledge while still in school Develop algorithmic thinking skills that extend beyond programming Get trained by top competitive programmers from around the world Experience real-world contest settings Become part of India’s top CP community

Dates: May 25 — June 6th, 2025

Location: NST-Rishihood Campus, Delhi

Apply Here

Hope you enjoyed the contest. The problems turned out slightly harder than intended.

Congratulations to top 5 on Div $$$1$$$:

• Rank $$$1$$$ : potato167
• Rank $$$2$$$ : maspy
• Rank $$$3$$$ : liympanda
• Rank $$$4$$$ : catgirl
• Rank $$$5$$$ : kuhqku

Recently, the account of Jaskaran Singh — s_jaskaran_s was hacked by someone. The hacker changed the password and email address of the account and he is not able to recover it. He got to know when someone asked him if he was selling his account. He was told that someone on Telegram was selling his account.

MikeMirzayanov Can you please help him in recovering his account so that it isn't wrongly used by other people?

UPD : The account has been recovered with the help of one of the sellers.

We invite you to participate in CodeChef’s Starters 181, this Wednesday, 9th April, rated for all.

Time: 8:00 PM — 10:30 PM IST

Joining us on the problem setting panel are:

• Contest Admin : Satyam satyam343, Shreyan Dominater069 Ray.

• Statement Verifier : Shreyan Dominater069 Ray.

• Text Editorialist :Nishank IceKnight1093 Suresh.

• Tester:Sushil SmolBrain Raaja.

• Setters: satyam343, wuhudsm, Think_Only_Once, sai-17.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

UPD : Here are the number of problems in each Division:

• Division $$$1$$$ : $$$6$$$ problems (and $$$2$$$ subtasks)
• Division $$$2$$$ : $$$6$$$ problems (and $$$1$$$ subtask)
• Division $$$3$$$ : $$$7$$$ problems (and $$$1$$$ subtask)
• Division $$$4$$$ : $$$8$$$ problems (and $$$1$$$ subtask)

Congratulations to Top 5!

• Rank $$$1$$$ : kotatsugame
• Rank $$$2$$$ : TKT_YI
• Rank $$$3$$$ : Rubikun
• Rank $$$4$$$ : potato167
• Rank $$$5$$$ : Nachia

We invite you to participate in CodeChef’s Starters 177, this Wednesday, 12th March, rated upto 5 stars (i.e. for users with rating < 2200).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin and Statement Verifier :Shreyan Dominater069 Ray.

• Text Editorialist — Nishank IceKnight1093 Suresh.

• Tester: Sushil SmolBrain Raaja.

• Setters:Shreyan Dominater069 Ray, beaten_by_ai.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

UPD : The number of problems in each division is as follows:

• Division $$$1$$$ : $$$6$$$ problems
• Division $$$2$$$ : $$$7$$$ problems
• Division $$$3$$$ & $$$4$$$ : $$$8$$$ problems

UPD 2 : Congratulations to the winners:

• Rank $$$1$$$ : liympanda
• Rank $$$2$$$ : harurun4635
• Rank $$$3$$$ : GOTKAKO
• Rank $$$4$$$ : noya2
• Rank $$$5$$$ : Kude

Hi everyone,

The ICPC Asia West Finals onsite round will be held tomorrow across several different locations.

We plan to host a stream covering the round. The stream link will be posted shortly. The problems will be posted in this blog when the contest starts. The editorial will be posted after the contest ends.

Contest Details

• Public ranklist Link — Ranklist
• Date & Time — 8th March 2025, Saturday, 10:00 IST (Tentative start time)
• Problem statements — NA
• Stream Links — AryanC Channel, Codechef Channel, AryanC Twitch

Hope you enjoy the contest! May the best teams win.

UPD 1 : The problem statements have been posted.

After a long wait, jeroenodb finally deservingly reached LGM. Many congratulations to him.

Previously, he had reached 2999 rating. Fortunately, this time he actually crossed the barrier.

We invite you to participate in CodeChef’s Starters 167, this Wednesday, 1st January, rated upto 5 stars (i.e. for users with rating < 2200).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin and Statement Verifier: Shreyan Dominater069 Ray

• Text Editorialists: Nishank IceKnight1093 Suresh

• Tester: Sushil SmolBrain Raaja

• Setters: Chromate chromate00, Shreyan Dominater069 Ray, Sushil SmolBrain Raaja, Think_Only_Once.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Hi everyone,

The second Indian ICPC Amritapuri onsite regional round will be held tomorrow in Bengaluru, Coimbatore and Kollam.

We plan to host a stream covering the round. The stream links will be posted shortly. The problems will be posted in this blog when the contest starts. The editorial will be posted after the contest ends.

Hope you enjoy the contest!

Contest Details

• Public ranklist Link — ICPC Amrita Website
• Date & Time — 29 December 2024, Sunday, 9:00 IST (Tentative start time)
• Duration — 5 Hours
• There will be 8 to 20 problems to solve
• Problem statements : NA
• Will follow standard ICPC scoring system (20 minutes penalty and 1 point per problem)
• The questions may not be sorted by difficulty
• Stream link — Codechef Channel AryanC Channel
• Mirror streams on — CodeChef and aryanc403 channel

UPD : The stream has started and the problem statements have been released. na

UPD 2 : The editorial has been uploaded in the same google drive as above.

UPD 3 : I also forgot to the post the ranklist. It can be found on ICPC Amrita Website. Congratulations to the Top 3 teams!

• Rank 1 : Ice Shard, CMI (10/12) : sheercold, Sid0309, Codula
• Rank 2 : on_the_spectrum, IITD (10/12) : MridulAhi, BladeRunner, etherinmatic
• Rank 3 : 404_solution_not_found, IITI (9/12) : nishkarsh, sai-17, P.V.Sekhar

UPD 4 : The jury solutions are also now available on the drive.

Hi everyone!

The first Indian ICPC onsite regional round was held today in Kanpur. I hope all of you enjoyed the contest. The results have been published at ICPC Kanpur Website.

The problems were authored by satyam343, chromate00 and me. We hope you enjoyed the problemset. You can find the problemset, editorial and jury solutions at NA.

Any feedback, positive or negative, about it would be most welcome.

Congratulations to Top 3 :

1. SubtasksWhere (IIITH), 11 / 12 — shiven, SmolBrain and hariaakash646.
2. poocha kya (IIT BHU), 10 / 12 — sv1shan, _helloLad and Atekichan.
3. segment_trACk (IITK), 10 / 12 — yuvrajKharayat, Ryshi and Sanat.

Hi everyone,

We are looking for tasks for the $$$3$$$ Indian Regionals and mainly, for the Asia West Finals. If you or anyone you know is interested, please fill this form

Dates of the Contests

• Kanpur Regional : 24th December. We will accept proposals till 16th December.
• Amritapuri Regional : 29th December. We will accept proposals till 20th December.
• Chennai Regional : 4th January. We will accept proposals till 25th December.
• Asia West Finals : sometime in March. We will accept proposals till 15th February.

Eligiblity

• You must not be a participant of the aforementioned regionals and Asia West finals
• You should have a max rating of at least $$$1800$$$ on Codeforces. (Special cases can be considered for this)

Compensation

Problem setters will be paid according to the following per-problem rates :

• Cakewalk (800 — 1000) : 800 INR
• Simple (1100 — 1300) : 1500 INR
• Easy (1400 — 1700) : 3000 INR
• Easy-Medium (1800 — 2100) : 5000 INR
• Medium (2200 — 2400) : 8000 INR
• Medium-Hard (2500 — 2800) : 12000 INR
• Hard (2900+) : 17000 INR

The ratings in the brackets are approximate Codeforces difficulties. Ultimately, the difficulty will be decided by the contest admin. We are mainly looking for the harder problems in the last $$$3 - 4$$$ categories.

If you are not free to prepare your problem, the preparation cost will be split 50 — 50 between the preparer and the author.

We invite you to participate in CodeChef’s Starters 162, this Wednesday, 27th November, rated upto 5 stars (i.e. for users with rating < 2200).

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin and Statement Verifier: Shreyan Dominater069 Ray

• Text Editorialists: Nishank IceKnight1093 Suresh

• Tester: Sushil SmolBrain Raaja

• Setters: Shreyan Dominater069 Ray, Sushil SmolBrain Raaja, Matthew chromate00 Roh

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Problem Distribution :

• Div1 : 5 problems
• Div2 : 6 problems
• Div3 : 7 problems
• Div4 : 8 problems

Congratulations to the Top 5!

Ranking :

• 1st : kdu_5
• 2nd : Egor
• 3rd : Kude
• 4th : physics0523
• 5th : wwwwodddd

We invite you to participate in CodeChef’s Starters 160, this Wednesday, 13th November, rated upto 5 stars (i.e. for users with rating < 2200)

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin and Statement Verifier: Shreyan Dominater069 Ray

• Tester: Sushil SmolBrain Raaja

• Text Editorialists: Nishank IceKnight1093 Suresh

• Setters: Nishank IceKnight1093 Suresh, Shreyan Dominater069 Ray, Sushil SmolBrain Raaja.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

The number of problems in each division is as follows :

• Division 1 : 4 problems + 1 subtask
• Division 2 : 5 problems + 1 subtask
• Division 3 : 6 problems + 1 subtask
• Division 4 : 7 problems + 1 subtask

Good Luck!

UPD 1 : The contest has been postponed for 30minutes and will now start at 8:30 PM IST due to a technical error. We apologize for any conveniences.

UPD 2 : The top $$$5$$$ standings are here. Congratulations to the winners!

1. Egor
2. wwwwodddd
3. potato167
4. liympanda
5. flytime

We invite you to participate in CodeChef’s Starters 158, this Wednesday, 30th October, rated upto 6 stars (i.e. for users with rating < 2500)

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin, and Statement Verifier: Shreyan Dominater069 Ray

• Tester: Sushil SmolBrain Raaja

• Text Editorialists: Nishank IceKnight1093 Suresh

• Setter: Shreyan Dominater069 Ray, Sushil SmolBrain Raaja, TheScrasse.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

UPD 1: The following is the number of problems:

• Div1 : 5 problems + 1 subtask
• Div2 : 7 problems
• Div3 : 7 problems
• Div4 : 8 problems

UPD 2: The contest got changed to rated upto 6 stars. I am sorry for the late change. We decided it was hard enough for 6 stars.

UPD 3 : Congratulations to Top 5!

• 1st Place : maspy
• 2nd Place : risujiroh
• 3rd Place : leaf1415
• 4th Place : noya2
• 5th Place : wwwwodddd

We invite you to participate in CodeChef’s Starters 156, this Wednesday, 16th October, rated upto 6 stars (i.e. for users with rating < 2500)

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Setter, Contest Admin, and Statement Verifier: Shreyan Dominater069 Ray

• Tester: Sushil SmolBrain Raaja

• Text Editorialists: Nishank IceKnight1093 Suresh.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

The following is the number of problems in each division :

• Division 1 : 5 problems
• Division 2 : 7 problems
• Division 3 : 7 problems
• Division 4 : 8 problems

There are no subtasks this time.

Good Luck!

Congratulations to Top 5!

• 1st Place : rniya
• 2nd Place : maspy
• 3rd Place : wwwwodddd
• 4th Place : potato167
• 5th Place : liympanda

We invite you to participate in CodeChef’s Starters 154, this Wednesday, 2nd October, rated upto 6 stars (i.e. for users with rating < 2500)

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Contest Admin: Shreyan Dominater069 Ray

• Setters: Sushil SmolBrain Raaja, Shreyan Dominater069 Ray

• Tester: Sushil SmolBrain Raaja

• Text Editorialists, and Statement Verifier: Nishank IceKnight1093 Suresh.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

I would like to thank redpanda and rewhile for their great help in writing and reviewing this blog. They are also the users who queried O1-mini for all the following problems.

We tried O1-mini on several problems, from a variety of sources. Let's list the results first.

Note :

• Some of the WA verdicts here actually means that the AI just "stopped thinking" which means the AI thought for a long enough time without any useable results so it ran into an error.

• All ratings mentioned are Codeforces ratings, the Atcoder ratings have been converted to codeforces rating. To measure the approximate codeforces rating of the atcoder problems mentioned here, you can use https://kenkoooo.com/atcoder/#/table/ + https://silverfoxxxy.github.io/rating-converter.

D2ABs

• 1762B - Make Array Good [1100] AC
• 1998B - Minimize Equal Sum Subarrays [1000] AC
• 1998A - Find K Distinct Points with Fixed Center [800] AC
• 1831A - Twin Permutations [800] AC
• 1831B - Array merging [1000] AC
• 1905B - Begginer's Zelda [1100] AC (this one even used 4o)
• 1905A - Constructive Problems [800] AC
• 2009C - The Legend of Freya the Frog [1100] AC
• 1816A - Ian Visits Mary [800] WA
• 1944B - Equal XOR [1100] WA
• 1758B - XOR = Average [900] WA

Standard problems

• 2000E - Photoshoot for Gorillas [1400] AC
• 13E - Holes [2700] AC after giving hidden test
• abc365_e — Xor Sigma Problem [1544] AC
• abc293_g — Triple Index [2037] AC
• abc258_g — Triangle [2181] AC
• abc342_g — Retroactive Range Chmax [2305] WA
• abc362_g — Count Substring Query [1940] TLE
• 1891F - A Growing Tree [2000] WA

ARC AB Problems

• arc174_b — Bought Review [1378] AC
• arc179_a — Partition [1092] AC
• arc183_a — Median of Good Sequences [1118] WA
• arc175_b — Parenthesis Arrangement [1410] WA

D2C+ (Non-standard) problems

• 1904D1 - Set To Max (Easy Version) [1600] WA
• 1904C - Array Game [1400] WA
• 1967A - Permutation Counting [1400] WA
• 1965A - Everything Nim [1400] WA
• 1943A - MEX Game 1 [1300] WA
• 1893A - Anonymous Informant [1400] WA
• agc051_a — Dodecagon [1842] WA
• agc043_a — Range Flip Find Route [1417] WA
• the famous 1188B - Count Pairs [2300] WA

Conclusion

Overview

• gpt o1-mini is very good and faster than humans at some standard problems ≤ atcoder blue, these types of problems can't appear in contests if we want fair contests where AI doesnt determine ranking

• gpt o1-mini is very good at most easy "adhoc" problems like D2AB and is faster than or as fast as tourist at these problems, I'm not certain about how to make D2A's that ai cant solve and D2B has limited options too.

• the AI struggles a lot on harder "adhoc" problems , especially multistep problems where the steps aren't standard

• Div1 people are completely unaffected (for now at least). Some extra care needs to go into choosing d2Bs such that O1-mini can't solve them, but otherwise Div2 contests are also mostly unaffected.

D2AB Ad-Hoc problems

It can "solve" most of the Div2AB level problems in under a minute. Why do i double quote around "solve"? Often, even when the AI can't really reason the solution, if the solution is simple enough like $$$min(a, b)$$$, it gets there by brute forcing.

It is hard to create problems which are suitable for such positions and still not solvable by beginners, but I don't believe it is impossible. We have 3 examples listed above ($$$1$$$ d2A and $$$2$$$ d2B), which are all constructive problems (and the construction isn't as simple as print $$$1, 2, ... n$$$). Constructive problems are one of the weaknesses of the AI, or more generally, problems where the ad-hoc part cannot be reached easily through bruteforcing.

It also failed arc183_a — Median of Good Sequences and 1943A - MEX Game 1, which are easy enough to be D2Bs.

$$$2$$$ tips in particular for easy problems i would like to stress on for problemsetters :

• Don't have them be a stupid (even if it is cute) result. For example, output $$$a + b$$$ or print $$$1, 2, .. n$$$.

• Try to have problems where genuine insight can't be easily replaced by guessing.

I know these are hard to do, especially for D2A. D2B might still be possible....and it is important if we try to make it as fair as possible.

Another option is to remove D2A and start at D2B (with registered => rated) with a less steep difficulty progress over the contest. There won't be a big difference for most participants however maybe completely new beginners will feel bad however if they solve no problems.

Standard Contests (ABC/Div3/Div4)

AI can perform exceedingly well in such contests. It is trained on infinite problems, and can recognize techniques with ease. For, example it solved the MO's problem in only $$$27$$$ seconds, while it took minutes for several Ad hoc problems (even when it managed to solve it)

These contests simply aren't fair in the current format. Even if you ban AI, i can always just understand and rewrite it's solution. I strongly urge one of the following $$$3$$$ actions :

• Remove them

• Have them unrated and solely for practice

• Rework them to not have so many Standard problems

$$$2$$$-nd option probably isn't very feasible, and you may not want to do the $$$1$$$-st. Thus, I suggest the $$$3$$$-rd.

Div2C+ Ad-hoc Problems

These problems generally need multi steps, and thus, the AI has a very low probability to solve it. It failed each and every one of the last $$$5$$$ D1As under 1400 rating.

Problems requiring some thinking which can't be easily replaced by brute-forcing solutions is the way to beat it, along with having multistep problems. With every non-trivial step (or even a trivial step given how the AI works) reduces the probability for the AI to solve the problem exponentially.

A meta shift needs to happen in the recent future, where we have to solely focus on making multistep problems with several thinking non-trivial steps. However, we are not there yet.

Rating Approximations

(These are purely approximations from the data we have, and is my personal opinion. They could be more accurate with more data but unfortunately we only have limited queries.)

• ABC, Div3, Div4 contests : [1900+] according to CF rating

• Div2 contests : [1500]

• ARC : [1300] according to CF rating

• Div1 & AGC : -

Final Remarks

We are mostly fine. Some amount of care needs to go to build easy problems which AI can't solve but other than that not majorly affected. Banning AI probably is the right move now however.

In the future, I don't see this type of "generate $$$10^9$$$ solutions and find the right one" AI being good at solving harder problems, especially if we try to counter it. An AI that can actually reason is much more dangerous imo...

We invite you to participate in CodeChef’s Starters 150, this Wednesday, 4th September, rated upto 6 stars (i.e. for users with rating < 2500)

Time: 8:00 PM — 10:30 PM IST

Joining us on the problem setting panel are:

• Setters: Shreyan Dominater069 Ray, Sushil SmolBrain Raaja U, Chongtian cry Ma

• Tester: Takuki tabr Kurokawa

• Contest Admin: Shreyan Dominater069 Ray

• Text Editorialists, and Statement Verifier: Nishank IceKnight1093 Suresh.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Here is the number of problems in each division :

• Division 1 : 5 problems + 1 subtask
• Division 2 : 6 problems + 2 subtasks
• Division 3 : 6 problems + 2 subtasks
• Division 4 : 7 problems + 2 subtasks

Please note that the contest is of 2.5 hours instead of the usual 2 hours.

Good Luck!

Hope you enjoyed the contest.

Congratulations to Top 5!

1. potato167

2. maspy

3. tiger2005

4. noimi
5. noya2

Recently, I got a request asking me to write down my thought process while solving questions. So, here is the promised blog.

I would like to thank IceKnight1093, qwexd, Sana, Everule and trash-can for proof reading and suggesting edits in the blog. Special thanks to satyam343 for discussing most of the blog with me.

1. Overview

The blog contains my solutions to $$$7$$$ problems in a wide range of ratings, starting from $$$1200$$$ all the way upto $$$2700$$$. Each problem has a step-by-step solution and you can notice how there are no large jumps in logic, but everything comes naturally. I do not claim that this is always possible in each problem, however I solve majority of CF problems in such a manner.

There are certainly other high rated people who will have completely different methods of solving. However, this is about what works for me. There are some meta ideas taken from parts of the solution and listed at the end in a "What can we learn?" section. I hope the blog is useful for you.

2. Some General Question Solving Strategies

Here is a non-exhaustive list of techniques that are useful to keep in mind. These are internalized by most experienced participants already but maybe it helps you.

• Figuring out the Nature of an Optimal Solution. One of the most important thing in problems imo.

• Solving subtasks of the original problem and then trying to extend/generalize your solution.

• Fixing a parameter and then trying to maximise the result with respect to that fixed parameter.

• Finding necessary and sufficient conditions. Sometimes, your necessary conditions themselves become sufficient, or vice versa.

• Identifying Lower and Upper bounds, and constructing them.

• Reducing a problem into smaller subproblems, commonly used with Dynamic Programming or Inductive Proofs.

• Considering the Decision Version of the Problem instead. Especially useful in Counting problems, where you need to count number of good subsequences for example.

• Formalizing the Problem

3. Questions and Solutions Section

Question 1. 1979C - Earning on Bets

Question 2. 1987D - World is Mine

Question 3. 1977C - Nikita and LCM

Question 4. 1889B - Doremy's Connecting Plan

Question 5. 2002D1 - DFS Checker (Easy Version)

Question 6. 1930E - 2..3...4.... Wonderful! Wonderful!

Question 7. 2003E1 - Turtle and Inversions (Easy Version)

Disclaimer : My solution differs from the editorial completely. You can read the editorial for their approach. I will present mine. Try to extend to the hard version of the problem from this.

4. About Stress Testing

Something which a lot of low rated participants do wrong : They don't stress test.

There have even been contests where I stress tested $$$3$$$ problems. I tend to make a lot of errors while writing code and it is not easy to always catch those errors with manually reading or debugging. Learning the skill of stress testing is insanely useful (and you don't need any tools for it, I do it all in the same piece of code without taking much time).

This was the first problem (I think) that i had stress tested during contest : 1854A1 - Dual (Easy Version) I was still done within $$$12$$$ minutes and it took me less than $$$5$$$ mins to stress test, and fix my bug (this is an easy example though as I didn't have to write a brute). My bug only occurred when all elements of the array were equal and negative, I don't think I would manually be able to catch that.

1987F1 - Interesting Problem (Easy Version) In the initial submission to this problem, I missed so many if-cases. I was very careless. But i managed to stress test and avoid more WAs. I think it took me 3 — 4 iterations of finding bug with stress test, fixing them and then again running stress test before my code was actually correct.

I highly recommend stress testing for you. It is simpler than you think : all you need is a brute function, and a generator. I usually replace my input function with a generator, and use a lambda function for the brute. It takes barely $$$5$$$ minutes to setup for most problems.

We invite you to participate in CodeChef’s Starters147, this Wednesday, 14th August, rated upto 5 stars (i.e. for users with rating < 2200)

Time: 8:00 PM — 10:00 PM IST

Joining us on the problem setting panel are:

• Setters: Shreyan Dominater069 Ray, Apoorv TyroWhizz Kumar, Kanhaiya notsoloud1 Mohan.

• Tester: Apoorv TyroWhizz Kumar

• Text Editorialists:Nishank IceKnight1093 Suresh.

• Statement Verifier:Kanhaiya notsoloud1 Mohan.

• Contest Admin :Shreyan Dominater069 Ray.

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest. The video editorials of the problems will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Hope to see you participating.

Good Luck!

Congratulations to Top 5!

1. maspy

2. redstar08

3. ecottea

4. tiger2005

5. kdu_5