Kogut_Ivan's blog

Codeforces Round 1043 (Div. 3)
By Kogut_Ivan, 13 months ago, translation, In English

Hello, Codeforces!

The TG channel team @KogutIvanTutoring is pleased to invite you to participate in Codeforces Round 1043 (Div. 3) on Aug/21/2025 17:35 (Moscow time) — another Codeforces round for the third division. This round will feature 6-8 problems selected in difficulty to create an interesting competition for participants with ratings up to 1600. However, anyone with a rating of 1600 or higher can register for the round out of competition.

The round will follow the rules of educational rounds. Thus, during the round, the problems will be tested on preliminary tests, and after the round, there will be a 12-hour phase of open hacking. After this phase, all successful attempts will be retested on successful hacks. We have tried to create decent tests — just like you, we will be disappointed if many solutions fail after the contest ends.

You will be offered 6-8 problems and 2 hours 15 minutes to solve them.

The penalty for an incorrect attempt in this round will be 10 minutes.

We remind you that only reliable participants of the third division will be included in the official results table. As stated in the link — this is a necessary measure to combat unsportsmanlike behavior. To qualify as a reliable participant of the third division, you must:

  • participate in at least five rated rounds (and solve at least one problem in each of them)
  • not have a rating point of 1900 or higher.

Regardless of whether you are a reliable participant of the third division or not, if your rating is below 1600, the round will be rated for you.

The problems were conceived and prepared by part of our team: fstilus, EzikBro, KotlechkovEgor, Wileyne, Friendiks, Boodoochai, pskobx

Also, a big thank you to:

Good luck to everyone!

UPD. Editorial is out!

  • Vote: I like it
  • -154
  • Vote: I do not like it

Comments Comments (63)
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13 months ago, hide # |
← Rev. 3  
Vote: I like it -17 Vote: I do not like it

Good luck to everyone, there's no FSTs in this contest!

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13 months ago, hide # |
 
Vote: I like it -58 Vote: I do not like it

yo guys, can you help me back to positive contribution?

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13 months ago, hide # |
 
Vote: I like it -8 Vote: I do not like it

hope this is the last div.3 i officially participate in

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13 months ago, hide # |
← Rev. 2  
Vote: I like it -36 Vote: I do not like it

I just want +ve delta 🥲

edit: why am i getting downvoted???

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13 months ago, hide # |
 
Vote: I like it +6 Vote: I do not like it

Hello, I participate for the first time in a competition , I didn't even know codeforces existed before today and I look forward to compete. Thanks, good luck to all.

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13 months ago, hide # |
 
Vote: I like it +22 Vote: I do not like it

There will officialy be Silksong news 5 minutes before the round. That'll either give me the boost straight for specialist, or make me want to kill myself. Let's hope it's the former.

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13 months ago, hide # |
 
Vote: I like it +5 Vote: I do not like it

I am looking forward to this game very much

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I hope it'll be good contest for everyone and I'll get a huge + delta.

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I will compete for being expert, I hope I do well and enjoy this round.

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Hoping to leave pupil this time

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Clashes with Silksong special announcement

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Vladosiya, cry, Proof_by_QED here?

I have to participate!

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13 months ago, hide # |
 
Vote: I like it +4 Vote: I do not like it

Finally , CF is back to ruin my day again :)

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13 months ago, hide # |
 
Vote: I like it -18 Vote: I do not like it

What a great contest!! Thanks to authours!!

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13 months ago, hide # |
 
Vote: I like it -25 Vote: I do not like it

Wishing high ratings to everyone!!

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

19k solves in B? CF is cooked.

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13 months ago, hide # |
 
Vote: I like it +4 Vote: I do not like it

MathForces

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13 months ago, hide # |
 
Vote: I like it +4 Vote: I do not like it

Was hard as Div2

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13 months ago, hide # |
 
Vote: I like it +12 Vote: I do not like it

C2 was tough, but such an amazing problem!

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13 months ago, hide # |
 
Vote: I like it +7 Vote: I do not like it

digitforces

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

How to solve D?

Can anyone please explain the approach??

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13 months ago, hide # |
 
Vote: I like it +10 Vote: I do not like it

Very very great contest! Just a little bit harder than its name

Also I was ranked 800 until 25 minutes before the end and now I see I'm 1900! How is that possible?

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

so bad contest as Div3 contest. i show that it was should be rated as Div2.

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13 months ago, hide # |
 
Vote: I like it -8 Vote: I do not like it

I don’t like pD It’s so annoying

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13 months ago, hide # |
 
Vote: I like it +17 Vote: I do not like it

Guys!! I have attended in a math olympiad for the first time in my life. Thanks for the Contest !!

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13 months ago, hide # |
← Rev. 2  
Vote: I like it +19 Vote: I do not like it

F and G are entirely cobbled together by forcing multiple different templates. It's really extremely boring to set such questions.

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13 months ago, hide # |
 
Vote: I like it +12 Vote: I do not like it

I got negative delta on this contest because while doing one of the problems, I saw a picture of the newly revealed mega victreebel (pic below) and could not properly debug my code while laughing for 45 minutes.

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13 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

d is way too standard and solvable with the following 2 links with very little modification

https://www.geeksforgeeks.org/competitive-programming/cses-solutions-digit-queries/

https://stackoverflow.com/questions/73821319/number-of-occurrences-of-digit-in-numbers-from-0-to-n

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13 months ago, hide # |
 
Vote: I like it -8 Vote: I do not like it

Something like digit DP seems to be too complicate for a problem D. Do you have any simple solution?

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13 months ago, hide # |
← Rev. 2  
Vote: I like it +10 Vote: I do not like it

My god, problem $$$D$$$ is implementation hell. I got the idea quickly of binary search and we can use Digit DP to find sum of digits of numbers in a range, but was not able to complete the implementation in time :(

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13 months ago, hide # |
 
Vote: I like it +11 Vote: I do not like it

problem D is awful

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I'm trying to solve D and going as far as:

  • got the k when n is 10**x
  • got the digit sum when n is 10**x
  • with k what is the current digit

But to figured what is the exact sum with k is some number is still doesn't quite there yet, can someone teach me how to approach similar problem more efficiently?

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    13 months ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    You first need to see how many numbers this sequence has For example, you can start by subtracting 9 from k, then 90*2=180, then 900*3=2700, etc., and finally, with a little attention to detail, you get the number of numbers After that, you can easily solve it (you can search for the sum of the digits of numbers 1 to n on Google) Also, the last number, which only needs to be calculated for some of its digits, must be calculated separately

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      13 months ago, hide # ^ |
       
      Vote: I like it 0 Vote: I do not like it

      ah right I forgot with what I have is the number digit of n, so at that point I can figured the digit = number of cycles count...

      I just suck at digit DP stuff

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

div3 or div2 + div3?

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13 months ago, hide # |
 
Vote: I like it +10 Vote: I do not like it

Cheers to ChatGPT!!

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Does anyone know more problems like D (ignoring cses)

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13 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

C1 was easier than B. C2 was a really good problem.

I think most of the downvotes on this blog are because of the math heavy problems from B to D.

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

YAY

MY PRAYER HAS BEEEEN A/C

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13 months ago, hide # |
← Rev. 4  
Vote: I like it 0 Vote: I do not like it

Almost every newbie, pupil, specialist of top 100-200 have one or more than one AI code. Why CF are not banning them, why only skip their solution. If a person cheat this time, and you only skip his solution, next time he will make sure that his code looks like more human written.

And I do not understand the mindset of these Indian college students. Every where I see most of them are Indian engineering students. Bro, you might get a job by cheating, but you won't survive in the culture. Every day companies are laying off people, you might get one job easily by cheating, but for other job you will struggle a lot. Even some companies are moving to in-person interviews because of cheating. Stop doing cheating, and start studying.

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Why are the ranks shown in friend and common standings different ?

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13 months ago, hide # |
 
Vote: I like it +2 Vote: I do not like it

Dudes were too lazy to make a contest, so they just gave us a math exam instead.

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

In C1

vector <long long> cost;
    long long c = 3;
    long long cnt = 1;
    for (int i = 0; i < 21; ++i) {
        cost.push_back(c);
        c = 3 * c + cnt;
        cnt *= 3;
    }

why this code is calculating the cost for each 3^x correctly? The formula was 3^(x+1) + x * 3^(x-1) but we aren't using this. For more please see editorial.

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

How does the standing system work? It shows that my official common standing is 3372 yet in the contest section in my profile, my rank is displayed to be 4517.

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    13 months ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    The official standings only contain trusted participants (who participated in 5+ rated rounds). For rating calculation, every participant whose rating is below 1600 is considered, regardless of trusted or not. The rank shown in your profile page is the position among the latter set of people.

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Dear Codeforces Team,

I am writing to respond to the notice about my solution (ID: 334878052) being similar to others. I want to clearly say that I did not cheat and did not share my code with anyone.

I created the solution by myself. I first thought through the main ideas on paper and made sure they were correct before writing any code. For testing, I used an online compiler (GeeksforGeeks compiler and some time other online IDE also), which I have done before in past contests. Now I understand that using such websites might make my code visible to others, which could explain the similarities. I feel really sorry about this mistake.

I want to make it clear that I never meant to break the rules. From now on, I will only use my local computer for writing and testing code to avoid any such issues in the future.

I apologize if this situation has worried anyone, and I hope you can consider my explanation. I care a lot about the fairness of competitive programming and the Codeforces community. I am committed to following the rules and maintaining the standards of this platform.

Respectfully, abhi00100 2132E - Соревнование по арифметике Codeforces Round 519 by Botan Investments

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13 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Got a TLE on the 4th problem with only 7 minutes left. Replaced a nested while loop with an O(1) arithmetic trick and got #Accepted just 3 minutes before the final whistle. Siuuu... #Codeforces

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