Hey Everyone!

This is something I observed while practicing problems according to tags. When you select multiple tags in problemset filter, it'll show you problems which contains all of the tags selected. Basically it kind of do an intersection operation and show problems having all the tags mentioned present.

Wouldn't it be great, if rather than showing the problems with all the tags mentioned, it would show problems with union of mentioned tags, which means all the problems which have at least one tag mentioned in the filter will appear.

What do you people think?

UPDATE : You can find a tag "combine tags by OR" in the tags itself. Thanks to mustard_with_fries69420

Here's an example of what happens now,

I didn't find any info. regarding this, so posting this blog.

The contest dates are February 22, 2023 — February 22, 2023, while the registrations are open between February 16, 2023 — March 08, 2023.

Is it some sort of mistake?

Hey Everyone.

I have been working on CF Edu Section Binary Search Playlist, which will consist of total 22 videos for each problem.

Actually, when I started solving the Edu Section Binary Search topic, I was unable to find videos for many of it's problems on YouTube and got stuck for quite some time. Since then I had this thought of making the whole playlist myself. So, I started making the solution videos for the Binary Search topic practice problems, and currently I have posted 7 videos in the playlist, including 4 videos for Step 1, and 3 videos for Step 2.

The reason for writing down this blog is to get some feedback from the CF community on the videos I made, so that I can do any required changes or rectify any unintended issue, in the upcoming videos for the playlist.

I hope you people will find this playlist helpful.

Link to the Playlist : CF Edu Section Binary Search Playlist

P.S. : I'm new to YT and making videos, so pardon me for any pronunciation or Naïve technical mistakes. I'll surely try to rectify them in the future.

Hello CF community! Today I thought for some time, whether I should write this blog or not, as I don't have anything, one can say solid as a proof, other than mutual belief of some of my friends and some consistent practice.

I know, most probably, it's quite hard to change that tag now, but to get your insights about this thing and understand it, I decided to write this blog.

Recently, in the Codeforces Round 842, my solution got skipped for Problem C, stating that it significantly coincides with some other people's solution.

While I checked those solution, I indeed found my solution very similar to them, but this didn't happened first time to me. Many times, me and my friends solutions coincides as well, the only difference we see is of variable name difference and some other minor things, thankfully it didn't happened in any contest yet (happened during just usual problem solving).

But this time, it got skipped! I got a bit low after I received this message, the first thing I start to do is, checking other peoples code who got skipped too, and genuinely I find it very similar. But on the other hand some of my friend (not the ones I personally know, just CF friends), during contest submitted almost similar solution as me, and yet they have AC till now.

It's not about why they had that AC & I got skipped, but more about, the solution to the problem C I later wrote (after messing up initially and getting WA) could possibly be similar to many other's as it was a normal greedy in my opinion. I did checked some ACs as well. You too can check the problem here

For an instance, check my skipped solution : click

And this AC solution is also very very similar to my solution (not sharing the link, as I don't want anything to happen to their AC status too)

Also this one which is also an AC solution

And many other like these.

I found them quite similar as well, because probably the way of writing is quite similar, just some variable difference.

One more thing I can say is : you can check my two earlier submissions, which I messed up in, had the similar idea, but I wrote bad long code, and got a bit stuck during the contest, but I sticked to the main Idea and wrote the AC solution again, obviously taking some time. Here they are : WA1 WA2

At last, I just want to ask what you people think about the solutions for common greedy like problems, which could have similar solutions?

Also, after discussing with one of my friend, I got one more doubt as he pointed it out to me. Although I'm not considering it in my case, as my submission time was rather late.

The doubt is, if someone solves a problem and locks it. And if they want to mess with someone else in their room by seeing and sharing other's solution in some groups, wouldn't that be a problem? How would someone get to know who did that? And even if we're able to find it out, wouldn't it be quite messy to handle such scenarios even for the Mike & Team if this practice gets too common? And the person who even don't want to get into this thing, too will get plagiarized.

Namaste Everyone! A very Happy New Year to everyone in advance :) Hope you're enjoying this time.

I was checking a problem's tag in Chrome's incognito mode, when I saw a gap in my profile (in the heat map) and I wasn't logged in at that time.

I got a bit scared, as I'm maintaining streak for some time and want to carry it on for at least an year. I solved one question on that date as well. See, it's showing "134 days in a row max".

I refreshed the screen some times, cleared cache of my browser, checked again (but this time logged in), and everything was normal, with no gap. See, it's showing "138 days in a row max".

I blamed it on cookies then, or some other technicality (my noob assumption)...

But, later I again checked without logging into Cf, & again it showed that gap.

Although, now I'm somewhat satisfied, as it's not showing it in my actual streak (You can see in the 2nd image above, with a total of 138 days in a row max.), yet I'm a bit curious, why it's showing that gap in my profile when I'm not logged in into Cf.

Note : That gap date is 28/12/2022, and I solved just 1 problem that day.

I was searching for this question, but didn't find it anywhere. I was wondering that some contests with a minor hardness deflection in like Problem C & D is justifiable (where D is easier than C), but some contests literally have a big difference of hardness, yet they're assigned like that in a contest.

Some ex. of such Contests are :

Educational Codeforces Round 140

Codeforces Round 830

Codeforces Round 823

Codeforces Round 805

Codeforces Round 770

etc.

I was going through this blog to know, how ratings are assigned for problems in Codeforces, and broadly it's quite related to how many submission a problem is having with participants of various ratings.

Although, such contests, as mentioned above, are really very few if we see overall contests, yet out of curiosity I was thinking, don't they affect the rating of a problem actually? Because, if let's say C is harder than D, then a lot of people will spend more time on C & probability of solving D will decrease because of that, which will lead to an increased rating assignment to it, when it might not be even worth the rating.

So, my question is, is there an explicit check for such scenarios to rectify the actual rating accordingly and, why do problem setters decides to assign problem in such sequence, is it coincidental or intentional? Because with minor difference, it's understandable, but I don't think it's coincidental, when that difference is quite considerable.

In recent Codeforces round #831, I got TLE in the final Test Set (Pretests passed successfully) of Problem B for this submission

I then again submitted this exact same solution but replacing >= with > in my cmp function and it got accepted. Accepted Solution.

I'm unable to understand why I got TLE in my original solution. Please help me with this.

Problem

Submission 1 : AC

Submission 2 : WA

The only difference between Submission 1 and Submission 2 is that, in Submission 1 I'm using a self made square root function, while in Submission 2, I'm using the C++ STL sqrt function, otherwise everything else is identical. Should it be considered as an inconsistency in C++ STL sqrt function? If not, why?

In the AtCoder Beginner Contest 271, I made two submissions for Problem D.

Submission 1, which is an AC.

Submission 2, which is a WA.

In Submission 1, I declared dp as int dp[101][10001]; globally, and used memset(dp, -1, sizeof(dp)); inside main function. In Submission 2, I declared dp as vector<vector<int>> dp(101, vector<int>(10001, -1)); inside main function, and passed it in function 'f' by reference.

I'm clueless about what is causing this WA in Submission 2, when the logic remains same. Could someone please help me with this.

In the last Educational Codeforces Round 134, I did a submission for Problem B. In this submission, I got a TLE. While this submission got Accepted.

The only difference both of these codes are having, is of the "abs()" function. When I used "abs()" (Although, it was redundant) it gave TLE, no loops nothing. And when I just removed (effectively) "abs()" in it, it got Accepted.

I'm wondering if "abs()" alone can cause this TLE, or there is something, very subtle about it, which was causing it. Please refer to the Links given above for both of my submissions and, in case you want to see it, the problem.

*Edit 1 : Apart from whatever mentioned above, this submission also has a difference of "vector<vector> grd(n, vector(m, 0));" (which again is a redundant thing as per the logic of code)

This doesn't seem to be causing any TLE, or is it?