Roughly, if you are looking for just Competitive Mathematics related Duels, there's a website called http://www.matiks.com/. It has mobile application too and gamifies mathematics. Try it to see if this is what you were looking for.

Some submissions had implemented it using Dynamic Programming too. I noted in a few on the top of standings, for example: Kevin114514, Radewoosh.

I just checked the Login/Sign Up page and saw that it accepts either a Mail ID + Password, or Google OAuth. Would it be possible to add a direct Single Sign-On (SSO) login using CodeForces, if its API provides this?

I don't think that it will be a fair range of division, as then Div-1, when kept exclusive, will be of 2400+ rated Grandmasters only (i.e., red coders, GM, IGM, LGM, 4000+), which leaves them a very little participant competition. And if the reason is simply to have rated contests, having more contributors for Div-1 contest problems is what could help have the existing Div-1s more frequently.

Also, having Masters and International Masters (IMs) in our Div-2 contests further pushes the current Div-2 participants to a tougher competition, which would make it tougher for them to ace them with better rankings. So, this is not a feasible solution.

This indicates an Ad-hoc / Cake-walk / Easy problem A (the first one).

Here's an interesting blog on the unordered_map Hash hack explanation following which you may choose to use them with an improved wrapper: https://mirror.codeforces.com/blog/entry/132929.

Time value with the diminishing score of an accepted submission. I've faced this one on CodeForces first and then on a TopCoder round.

For your profile, I won't agree that it is stuck. You had just started months ago, and CodeForces problems are no cakewalk. They accept solutions after running them through good amount and quality of testcases, which catches most of failing (verdicts like WA/RE), almost passing and even passing but slower than expected (TLE verdict). I had been in your situation, if you look at my graph, you may feel that my peak isn't up to the average profiles that have this time span of attending contests. I know my reasons (not upsolving enough, yet to study several advanced topics, and sometimes just losing on mistakes).

I would keep it short and suggest that take your time in building the expertise and find out what works best to boost your performance. You can refer the other such existing blogs too, and welcome to the sport of CP.

After the contest ends, all participants can post their approach on the Editorial tab. Please share your approach.

Wow, this is new for me. I have only been able to participate (with at least 1 AC submission) in AtCoder Beginner Contests (ABC) and seen AtCoder Regular Contest (ARC) editorials which do not have this approach suggestion feature on the Editorial tab. Good to see this.

May not be optimal. Did you just try with 9s or even tried 99, 999, ... which can go TLE but not wrong?

Is registration at https://iicpc.com only meant for students? I see a mandatory Graduation Year field which only provides options from 2025 to 2029 and another School option for under-university schooling students.

I will be able to participate directly on CodeChef Starters 173, but I didn't see any eligibility criteria mentioned for registration. I see a comment that only students are eligible for prizes. Please confirm on who should go for registration as well.

That's right. It's in place then. :)

If 998 F and G were difficult than this one's, then even that wasn't a Div. 4 level round

Don't fret. Learn with this problem experience and hopefully it will help you gain rating in the future rounds :)

Yes, simple logic is that if any consecutive matching characters are present, then the answer is straightaway 1 as the two characters can be replaced by any character, which can always be another neighbouring character that continues the match of two adjacent characters for another replacement until it reaches 1. To check for adjacency, a simple loop on the indices can be used. If no such adjacent matching characters were found, the entire length of the string will remain as-is without any operation, giving answer as the length of the original string.

Hovering on one such Badge gives, "Badge of honor for supporting Codeforces on its 8th anniversary". Perhaps some form of support (monetary or non-monetary) would bring this badge to the selected participants, cause not all of the old accounts have even got one.

I understand your decision. Still, I would request to consider listing national Olympiads too as not all of the listings currently accept worldwide participation. So, if Europe, Asia and Africa level entries have made it to the list, then within these continental categories you may list the national regions as well.

Indian National Olympiad in Informatics, 2025 (INOI-2025) to be held on Sunday, 9th February 2025 from 2PM — 5PM.

Reference: https://www.iarcs.org.in/inoi/current.php#ico2025

Please update this data too on your blog.

That's a good reference. Thank you for sharing it.

Trying to open the Testcase explanation image in a new tab gives this PNG: https://espresso.codeforces.com/762b4fec0fd1a6b4150f305d2407db01f71c3306.png

As PNG cannot show multiple frames like a GIF, it should be expected as a still image. In case a PNG preview has been generated out of an uploaded GIF, the problem setter may provide the multiple shots separately or somehow share the GIF instead.

Please open up solution links too, currently trying to access the link throws "You are not allowed to view the requested page" error notification.

You're welcome.

Just checked, updated ratings have already reflected on our profile rating and graph. So, it takes under ~1.5 hours to update ratings post a Starters contest.

Direct Link: https://mirror.codeforces.com/contest/1699/problem/B

Number of successful submissions on the most solved three problems make it look like that. I could only solve the Delete Not Equal (DELNQ) and Lottery Tickets (LOTTERYTICK), and found Grid Construction (Odd) and Grid Construction (Even) in the increasing order of difficulty.

Ratings are usually updated in a day. (I too don't recall the precise timing).

You will get the exact rating as shown on the Live Ratings section on the right pane of the Contest Page. I have been getting the exact same as shown on this right section at 120 min. (i.e., end of 2-hour contest duration) even though they say plagiarising users get a rating drop later when checks complete which makes me wonder if they get even eliminated from the leaderboard or not for genuine participants to get the right ratings deserved in a contest.

For all of 1-star rated users in your leaderboard, you had most-likely participated under the their Division 4 which is for users with rating $$$ \lt 1400$$$. Other rated users will participate in different divisions (Div. 1 to 3) as per their rating band. The thresholds for ratings are given at the main contest page. For Example: https://www.codechef.com/START167 will include the Link to the Division-wise pages and explain the bounds of ratings which fit in each division. 5-stars and above will come under Div. 1 here https://www.codechef.com/START167A, while ratings will be impacted only for up to 5-star rated coders.

Div 1 + 2 (All Divs. combined)

Yes, I was able to implement it for search within a range. Check this Python 3 solution: https://mirror.codeforces.com/contest/2051/submission/297906734

Try to read through the implementation, instead of conventional check on a value, it checks for the value being $$$ \lt $$$ lower bound ( = $$$\Sigma - a[i] - y$$$ given max. sum ), $$$ \gt $$$ upper bound ( = $$$\Sigma - a[i] - x$$$ given min. sum ), or being in the range with >= lower bound and <= upper bound.

In case you wonder about the bounds, $$$\Sigma - a[i] - a[j] \lt x \implies \Sigma - a[i] - x \lt a[j]$$$ holds as long as the values are non-negative.

Many people solved C1 and higher difficulty problems, so your rank dropped to 6000+ out of ~9100+ which gets calculated as a slightly lower performance than your last rating.

You can check more on rating calculation at https://mirror.codeforces.com/blog/entry/20762 or try out some CodeForces Rating Predictor for a better view on the rank vs rating.

You've saved us an unexpected TLE! :clapping:

Yes, it is also noted under the editorial for Problem B that Set and Dictionary uses same Hash function. But, my understanding is that as Set only stores a single occurrence of an element, there's only that single entry in that Set that will be subject to that collision with every matching hash attempt, unlike a Dictionary where that entry also buckets corresponding values to that key. Please do suggest if you have any such testcase which may fail this submission. I would have been amazed to see it getting hacked on this possibility too.

As a Pythonist participant, thanks for covering test 4 on Problem B that gives TLE verdict with dictionaries. I too got this verdict: Submission 291964656 Then, using set for tracking a prior occurrence worked on Submission 291974200 , instead of having to rely on the suggested collections.Counter().

Will have to see if this get hacked or failed in any of the main test.

It worked for me. As I wasn't able to deduce the direct formula used for the else part in the suggested editorial solution for case when $$$b != 0$$$, I had realized using Binary Search for the problem B.

If it works in PyPy3 (Python implementation of Python 3), it should work on most of the languages. Check out my Binary Search inclusive solution to Problem B here: https://mirror.codeforces.com/contest/2028/submission/290951271

The entire contest was authored by a single author, it's clear from that.

System Testing may have begun, it gets completed in ~1 hour or lesser depending on the pretests accepted submissions.

Though submissions will be available now, you can use the status tab as soon as a contest finishes to view and filter other submissions.

Being a CodeForces Gym contest, it won't be rated.

Pupil when mentioned, back to Specialist when commented. Good Going, hoping your problems to challenge and be challenged.

An unthanked tester? :sarcasm: Let the problems befool!

Thanks for posting it.

Is it an unrated one? Just clarifying to ensure whether a participation would impact my rating or not?

Update: As a Gym contest, it will not be rated for sure.

Yes, with a 50% sub-task scored as well. Agree Disagree

If it's tried, "You cannot vote twice. You have already voted for this comment before."

CodeForces using largest common prefix as title for common contests? It went incorrect for today's contests.

• Needs to be fixed
• Seems Good

1) When did you start programming? : Around 2013, School Class 6th, 13 Years Old (with QBASIC in class curriculum)

2) When did you start competitive programming? : Around 2020, College under graduation (B. Tech.) 2nd Year, 20 Years Old (with HackerRank and CodeChef)

Your sliding window loop does not actually consider the correct window, instead of:

...
    for (int i = k; i < n; i++)
    { 
        // adding next character at right in window
        if (s[i] == 'B')
            ++b;
        else
            ++w;
        // removing previous character from left in window (wrong! should happen after your ans is checked!)
        if (s[k - i] == 'B')
            --b;
        else
            --w;
        ans = min(ans, w);    // Here, your window does not consider the starting character
    }
    cout << (ans > 0 ? ans : 0) << "\n";
...

You should have firstly checked for ans= min(ans, w) before removing the initial window character out, just like:

...
    for (int i = k; i < n; i++)
    {
        if (s[i] == 'B')
            ++b;
        else
            ++w;
        ans = min(ans, w);      // Correct Place for finding answer
        if (s[k - i] == 'B')
            --b;
        else
            --w;
    }
    cout << (ans > 0 ? ans : 0) << "\n";
...

Only Comments are additional, to help you understand dukhi_insaan. See if it helps!

Yes! Sometimes $$$B$$$ is more indirect and confusing than $$$C$$$. I too spent slightly more time on problem B than C:

You have linearly searched for the query in your prefix sums array. While the approach is not wrong, under the given constraints of sum of $$$N$$$ and $$$Q$$$ over all cases to go up to $$$1.5 * 1e5 = 150000$$$, which can cause Time Limit Exceeded (TLE) on higher values, close to the constraint limits.

Maybe you have gone through Problem E instead of Problem D, or could have mentioned it otherwise?

Yes, they are usually rated (AtCoder Regular Contests are rated for ratings up to 2799 in their platform).

Around the end of last year, 2021, AtCoder has started providing options to register for a Rated contest either as Rated Participant or Unrated Participant. If you do a Rated Registration against a competition, be sure to participate in it because it will affect your rating whether or not you participate in that contest, or unregister at least 5 minutes before the contest begins.

More information regarding it here, in their post on it: https://atcoder.jp/posts/745

Could be possible that multiple people may have pressed it concurrently.

Unlike voting (the one that affects our contribution), these are revertible at least. Also, we can leave a like to our own widget too.

• Yes, better:
• No/ Didn't get:

Case insensitive handle links allowed me to change my handle without any need to update my CodeForces public profile link.

Really, the magic is amazing!

Unrated, Headquarters accounts have it

Wow! This is actually a better solution than what the blog suggests, in my opinion! "Minimally disruptive" for this timeframe is something to be taken care of!

If we get this option, I feel it would be better if the count of messages isn't displayed within the contest window, else participants like me might get curious and wonder about what's coming in until the contest ends.

I'm glad it helped :)

Hey yazzz, good to see that you've already figured a way out, passing 'in' file with code execution command on terminal as: python3 py_program.py < in.

I would like to add to your answer by mentioning one other alternative that seems to work fine in my Ubuntu 20.04. The one way out for me is to firstly check if there's my input file in the code or not, and then use it to replace the standard input (STDIN) in Python 3 for our code runtime using open() file handling method. The corresponding code snippet for the same is as follows (assuming input file is named 'in.txt'):

import os           # importing to use os.path.exists method to check for input file availability
import sys          # sys.stdin would be replaced for our runtime using this

if os.path.exists("in.txt"):
    sys.stdin = open("in.txt", "r")

# ... Your code can follow from here on as usual, using input() ...

Following this above code snippet, your Python program shall take any inputs from the specified input file now. You can skip using os.path.exists() method here by using try-except to handle FileNotFoundError.

Note: This one works for me at least in Ubuntu, haven't tried it on other OSs like Windows and Mac yet. Any confirmation on it will be appreciated :)

This is primarily because the time may vary from place to place, as per their time zone. timeanddate.com URLs can help with directly showing time converted in the local timezone, thus saves the confusion and hassle of converting them manually.

I have had the same question after reading this post. Thank goodness, I've read this before posting this query. :D

Now that I'm thinking, it could be possible that they might be setting Div 3 contests mostly themselves (since they're not very frequent here, as much as I've seen), and might be accepting easier questionnaire as a voluntary contribution, or might be paid based on their quality.

P.S.: Just a thought, no declarations included!

Launch your own copy of CodeForces ;)