Top Comments

And here's something special: Solve problems and make a difference! Yes, you heard it right, just like my last contest, this time as well you can help the world just by solving problems. I will donate money to the underprivileged people in my neighborhood based on the solve count of each problem by the following measure:

Donation Per AC

You can check how it went the last time I did this: https://codeforces.me/blog/entry/96333#comment-907470

Also, the top $$$5$$$ Bangladeshi contestants will receive $$$1000, 800, 700, 600,$$$ and $$$500$$$ BDT respectively from me as a small gift!

Note that neither TON nor Codeforces has anything to do with the donation or the gift.

Not me guessing difficulties by USD

I only received the message yesterday that YouKn0wWho's round requires an alternative problem, and the coordinator needs to select a problem from my round (which you previously coordinated). We are struggling with selecting problems and fixing bugs. We only confirmed the final problemset a few hours ago. And I expect to notify you after participating in today's codechef round. Overall, I apologize for not communicating with you in a timely manner.

On elsantodel90IOI 2025 Call for Tasks, 39 hours ago
+63

Submission deadline 29th December 2025 doesn't look right.

Solutions (SubtasksWhere)

E (bincatmod)
C (Points and Threads)
+50

遮沙避风了

Sorry, I overreacted. I didn't consider that the problem could have been just added......

toaster

As a tester, I can confirm that this round does indeed have problems.

+34

Meaningless. Please don't waste your time. It's a waste of time to read your unreadable blog.

On H_R_KMy luck.exe, 19 hours ago
+31

check my contest history to see what comes after 1599

Unlike the TON round 8, 256-1023 places lose their prizes, and 20 USDT is much less than 8 TON (8 TON > 8 * $5 = $40 = 40 USDT), which 128-255 places got in round 8.

Their settlement is also without TON now.

What happened to TON?

MAKISE KURISU!!!!

On H_R_KMy luck.exe, 12 hours ago
+24

I feel you.

+24

遮沙避风了

On elsantodel90IOI 2025 Call for Tasks, 28 hours ago
+22

They might accept anything. In IOI there are easy problems and hard problems

Bro can't you read?

As a tester, I didn't know I could have won $15,000 (just needed to beat a certain Belarusian...)

Y'all should give it a shot!!! Good luck.

As a tester, I can confirm that I tested this round.

Thanks for the contest. QUICKEXIT was such a beautiful problem!

I see tourist registed for this contest!

On hxu10My Meta hacker cup experience , 13 hours ago
+17

Reading this post was heartwarming. I'm glad you liked our problems, and I hope you get a top-200 shirt next year.

Meta has rejected my resume for SDE and MLE positions 12 times

I'm sad to see you had such a terrible experience with our recruiting team. Sometimes there are discrepancies between what the recruiters are focused on and what's ultimately in the long term best interest in the company. Sometimes there is just widespread systematic incompetence at making what seem like obviously good choices when there are lots of people involved in something big. I honestly have no idea how your resume got ignored 12 times. Obviously it shouldn't have. There's nothing I personally can do about it at the moment, but I just wanted to say I'm sorry, it's not your fault, and I'll do what I can to help our company make more reasonable decisions in the future.

BUMP

On DarkSilverDiameter of a graph?, 38 hours ago
+16

I'm pretty sure that in general graph you cannot do better than $$$O(N^2)$$$. Someone please correct me if I am wrong.

And is there a Euclidean Distance MST algo

+16

你说的挺完美,但肯定不对

+16

So why do you say you can't speak English but the sentence "I can't speak English" appears?

As a tester, this is the $$$4^{th}$$$ time in a row I found at least one problem in the round I tested really satisfying, and I hope people would feel the same.

As a tester I wish good luck to everyone!

+14

Your saying is perfect,but 100% incorrect.

change time/day icpc india clash

On SecondThreadHacker Cup Shirts 2024, 46 hours ago
+13

Kazakhstan is on the list now

Reminder: The contest starts in 30 minutes.

On _Randooom_What ?, 42 hours ago
+13

these kind of blogs are good, not all blogs on codeforces have to be useful and clever, a couple of them are just for fun and relaxation from tasks. I agree that second one is stupid, but the first one is pretty vital and funny

As a tester, hackerrank is kinda mid

Let me tell u sth about ArshiaDadras:

I officially started competitive programming and programming classes with Arshia Dadras four years ago. He is a very capable and ethical teacher. Thank you, Arshia, for being so great <3

On hxu10My Meta hacker cup experience , 29 hours ago
+13

Congratulations sir. Can you share or tell any compiler which is useful to use in MHC, like to generate output for those long test cases. Me noob only uses codeforces custom test everytime ;)

why 256-1023 places no prize this time :(

On hxu10My Meta hacker cup experience , 11 hours ago
+13

Of course. I mentioned I was 2800+ in leetcode contest, 2200+ in codeforces, top 500 in Google Code Jam and top 1000 in Meta hacker cup. What's more, I have a paper published in Science, which is extremely top journal in physics area. The only weakness is that I am not computer science major, and I need sponsorship.

However, this is still not strong enough. For every SDE position, there is 1000+ resumes waiting to be selected, which make the job application extremely competitive. It is normal that I am not the 1/1000.

On AkiLotusOn interactive problems, 8 hours ago
+13

People seem to not like problems that are different, and interactive problems typically have a different way than normally expected to solve. It requires a different mindset.

I think interactive problems are kind of fun. They can be frustrating, but they are unique.

People should just create habits for interactive problems, and continue with it as a normal problem. For me in C++, I just make sure to have cout << flush; and to comment out my fast IO. I don't know if that is even necessary, but I make that a habit for interactive problems and I never need to worry about the interactive part of the problem.

Thank you for reading this. I believe that if you struggle with what to do on the interactive portion of the problem, try a few interactive problems out. Try different ways of flushing the output, using the different types of input/output, etc. If you are comfortable with it outside of the contest, you can be comfortable with it inside the contest.

Thank you so much for your kind words and support, AmirParsa!

It’s truly a pleasure to be remembered in such a thoughtful way. I’m also really happy to see that you’re continuing to improve your coding skills.

Wishing you the best of luck in your journey, and I hope we get to meet in person soon!

On UTPC_AdminUTPC Fall 2024 Contest #5, 42 hours ago
+11

Thank you, I've just fixed it.

On _Randooom_What ?, 40 hours ago
+11

tbh im very shocked that blog became so popular, i posted it just for fun, but my friends liked the post, we just love memes about that, thats all

I struggled with ONETOTHREE during the contest and wondered why so many participants get AC with this problem, but after the contest, I noticed and was amazed that the following scheme is valid.

Spoiler

We can actually prove it by proving that we can never merge islands of 3's. (2's are fixed). I got 1e9+7 WAs before noticing that we have to run the loop backwards as well for smth like 233312 😭

if possible please change the time/date of the contest as icpc india preliminary contest will be held on the same day 23rd nov 21-23:30. so that we all can take part too!!

When I came up with the problem, I had a more complicated casework-y solution, and only later realized that the simple greedy implementation is actually correct.

I was not sure how guessable this was so I briefly considered modifying the problem to ask for the answer for every prefix or something like that, but after discussing with the tester we decided it's fine to keep it as-is, since for the most part I feel like if you're able to think of this algorithm then it's not too hard to prove it either. (Also it makes for a simple implementation which is always nice.)

I did make sure to modify the samples so that just iterating forward would pass them though :) (you're welcome RoomTemperatureIQ)

+10

Congratulations Screenwalkers! Our team(WayInWilderness) participate in Yokohama Regional from korea. So it would be fun watching the university of tokyo teams at scoreboard during the contest.

On AkiLotusOn interactive problems, 8 hours ago
+10

Same here. I (almost) always define all query syntaxes into functions accordingly, then forget about them and do the problems proper.

On elsantodel90IOI 2025 Call for Tasks, 28 hours ago
+9

I've seen problems around 1500

On SecondThreadHacker Cup Shirts 2024, 23 hours ago
+9

SecondThread I think there might be a bug in the form menu. I used tab to navigate to the next option, but it triggered submit instead. Now they confirmed it with an incomplete delivery information.

Pyqe but he's a newbie

+9

ChatGPT:

In English
In Chinese
On UTPC_AdminUTPC Fall 2024 Contest #5, 46 hours ago
+8

The link to the time says that the contest will be held on 06:00 (which should be 18:00)

Fixed time

I also need an official announcement :(

You can flex with "I have gold at an international olympiad"

On SecondThreadHacker Cup Shirts 2024, 40 hours ago
+8

I just copy pasted the text that they showed after i confirmed my order. That's why i used the quotes.

The timing of this contest overlaps with the India ICPC Prelims, and I really want to participate in both. Unfortunately, I’m torn between the two. :'(

On al95ireyiz[SUGGESTION] Test Cases, 21 hour(s) ago
+8

Yeah, I know the feeling. It’s so frustrating when you get “WA on test X” and all they show is some huge number instead of the actual test case. If they just showed the failed input, it’d save so much time and make debugging way easier. I’d rather figure it out myself than rely on the editorial, honestly.

On Hussien_Ibrahiemcodeforces is slow, 17 hours ago
+8

codeforces is so slow that this comment took me 7 years to send.

On 4o2aOptimality of today's E problem, 15 hours ago
+8

l0l

Spoiler

better than yours

+8

要不为啥以前打CF没问题

On AkiLotusOn interactive problems, 93 minutes ago
+8

My bad (but also, git gud)

clashing with icpc prelims india

Good to see that I finally get 7 stars after this contest. My profile

Why hackerrank instead of domjudge or codeforces?

This problem is the OV problem with $$$\log$$$ bits, it cannot be solved better than $$$\mathcal O(nv)$$$.

On H_R_KMy luck.exe, 19 hours ago
+6

Luck the matchmaker!!

+6

chUoNgnn (gold IOI 2024)

Best wishes to the round, contestants, and problem setters.

On SecondThreadHacker Cup Shirts 2024, 42 hours ago
+5

I believe FedEx wouldn’t ship from the US to Ukraine when the country list was compiled. I’m not sure if that has changed since. If so, our distributor’s website should be updated to reflect that.

On _Randooom_What ?, 40 hours ago
+5

привет легенда

As an author, please give me T-shirt too.

Great initiative vai. Amder moto gorib newbie der jonno ontoto akta problem raikhen vai request. jeno akta holeo solve korte pari vai.

On elsantodel90IOI 2025 Call for Tasks, 24 hours ago
+5

I believe the interesting question is whether it's possible to do it faster than O(n^2) due to the need to calculate distance between every pair of points, to which the following links may be useful:

manhattan

euclidean

As a tester, I liked to test my first round! :)

PS: If you win $15,000, please give me the T-Shirt, hahaha

+5

Why i can't understand what you said?

On AkiLotusOn interactive problems, 8 hours ago
+5

I think people have different opinions in interactive problems.

In my opinion,I like these problems because it's really interesting and it can widen my sight.

Some of these problem really helped me a lot to learn some algorithm that i have never seen.

Although sometimes it makes my rating dropped,I still enjoy it by its interesting,its unique glamour.

PS:I'm bad in English,but I try my best. :p

On AkiLotusOn interactive problems, 3 hours ago
+5

It's just about preference and about how much people are used to interactive problems. It's still not common to see many interactive problems outside of Codeforces. Even in CF, interactive problems are still taking only a small portion of the problemsets and they are avoided in D2B and easier problems due to the complexity of the problem format, lengthy description of the interaction process, and difficulty for testing. It's not something that's fundamentally hard (unlike the "advanced topics" you mentioned), but is something that you need to learn and spend some time to get used to.

It's no wonder why some people think it's a thing only for high-rated participants, because even if they very occasionally see interactive problems in their range, they can just skip those and it's usually not a huge matter even to reach Experts, and those are indeed the majority of people. For this reason, I'm actually welcome to introduce more interactive problems in somewhere mid-early in Div. 3 with only basic thought process required, so that people can easily get used to them and be prepared to confront them in Div. 2 legitimately.

+4

It's the same in Korea, though. The Seoul Regional is prioritized over the others.

It's a memory misuse problem, it happens when b is just after a in memory so the data inside b will be overwritten so u need to be careful using scanf() .

On SecondThreadHacker Cup Shirts 2024, 42 hours ago
+4

Can I have this year's chart size for t-shirt please SecondThread ?

On H_R_KMy luck.exe, 15 hours ago
+4

Needed 87 but got 86? So close, even the universe was like, 'Let’s keep it interesting' lol

On AkiLotusOn interactive problems, 5 hours ago
+4

The year is 2024 (no it's almost 2025 even what the heck) already, and why are interactives still uniquely discriminated?

They are not so much discriminated. Most people are fine with them. Complaints are from those who care much about their rating and is especially bad in interactives.

On AkiLotusOn interactive problems, 5 hours ago
+4

Yeah, it's indeed on the few. Yet it still amazed me that of all the scapegoats naggers tend to use for excuses, interactive always had a considerable portion.

Code For C
On RE_PrinceRating rollback?, 36 hours ago
+3

thanks guys for upvoting me :)

Wow, I chose to attempt G over F in the contest because I saw it had more solves...

it's genuinely easier if you knew what you needed in order to solve it though.

On elsantodel90IOI 2025 Call for Tasks, 29 hours ago
+3
On H_R_KMy luck.exe, 16 hours ago
+3

Congrats!

Same Same but Different!

On H_R_KMy luck.exe, 14 hours ago
+3

Same, I needed +70 for expert but got 1 less and then minus in next

:D
On hxu10My Meta hacker cup experience , 11 hours ago
+3

Thank you for your heartwarming comment and for organizing the contest. I also saw your previous version.

Yes, I applied for 2 positions in 2021, 3 positions in 2022, and 7 positions in 2023. This adds up to a total of 12 positions. I only got a recruiter call after 2023 Hacker cup. The conversation went well, but she ghosted me afterward. I didn't even made it to the phone screening.

I didn’t apply in 2024 because I already got a job at a startup company as a Quant C++ Developer at the beginning of this year. I’ve learned a lot in this position, so I’ve decided to stay with this company until November 2025. After that, I plan to apply to Meta again. By then, I will have at least two years of experience and will be more competitive for the role.

Points and Threads
Note that it is possible to avoid using cht to eliminate a log factor (though it wasn't necessary to get AC)

Hint
On AkiLotusOn interactive problems, 2 hours ago
+3

Yes, I liked 2037E - Kachina's Favorite Binary String in the last Div. 3, but this one wasn't so easy. I think something easier than this one that is not just straight "implement something" can be used for D3C/D3D.

I'm going to get over 2000 rating pts after this contest. Bet it!

To prevent me from breaking my promise, I declare that my AtCoder account is liwuyou.

You can use clist.by. It gives information not only for Codeforces, but other platforms too!