Rezwan.Arefin01's blog

By Rezwan.Arefin01, 15 months ago, In English,

Hello Everyone,
I guess everyone who is preparing for OI already know about this Checklist for OI Problems prepared by ko_osaga. I've been using this for quite a long time, and it is really helpful!

But since the checklist gets updated from time to time, I found it hard to migrate from the previous checklist to new checklist. So, I made the following web app for the same purpose! Now you don't need to worry about migrating, I can just add the problems to database and it'll update automatically!

Link: OI Checklist

Please find the features and changes to the main checklist bellow:

Features and Changes

  1. First of all, now the checklist contains direct link to each problem, while the main checklist had link to some parent of the link. And clicking on a contest name will lead to the official "Task" page of that contest, which generally contains judge data, editorial etc. In case this is not available, a related page is linked.

  2. Each category has a progress bar above it, so you can easily see how much you've solved.

  3. Many of us want to keep our checklist secret. Don't worry, you're checklist is always secret. However, you can share a static link your checklist.

  4. You can see statistics of a problem by hovering over the cell. Currently the statistics include the number of perfect scorer in official contest and the statistics that was given in IOI 2018, that is, the percentage of points that was scored at that problem during contest. So you can get used to this kind of stats.

  5. Toggling state of a problem is easy, just click on the cell. It will change state from unsolved to solving to solved.

  6. Some problems that are added in but not available for public is marked in red. Since shows that output only tasks is under testing, you can keep track of them. And problems that are not available or POI problems that doesn't have translation yes are marked in black.

Hope you'll like it. What other features would you like to see?
(This is not well tested yet. If you find any bugs please let me know)

UPDATE 1: As Benq suggested, now you can turn the state of a problem to an additional color: Blue. Meaning you already know the solution to the problem but don't intend to implement it for now. But the count of such problems will be added to solved problems for the status bars. The blue color is barely different from the green one as there is small difference between knowing solution and implementing it.

UPDATE 2: All USACO problems from session 2012-2013 to 2018-2019 are now added. Now the list contains 733 problems.

UPDATE 3: Some CEOI Problems were not available in, but they are available in, so updated all CEOI problems' links from Now BOI problems have direct links to the contest in (previously was linked with each of the BOI problems), same goes for CEOI problems.

UPDATE 4: Sorry :( The app has exceeded the free row limit in heroku. So, I've taken it down in Maintenance Mode. I'll keep the post updated if I manage to host it somewhere else. :(

UPDATE 5: Migrated from Heroku to PythonAnywhere. Now the app is running on All data from the previous app was imported into this. Yet if you find some inconsistency in your checklist please inform me. You may want to search your browser history and delete all entries of Happy practicing. :)

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By Rezwan.Arefin01, history, 18 months ago, In English,

Hello everyone!

We all know that JOI has a rich collection of high quality problems. But a fact is that almost all past problems are in Japanese, so many of us can't attempt to try / solve them.

Since Codeforces Polygon now supports setting OI Problems, I and some of my friends (ruhan.habib39, Mamnoon_Siam, Bruteforceman) took an initiative to translate the problems and upload them to Codeforces.

We will be having our first contest, JOI Spring Camp 2013 Day 1, today at 6:05 PM UTC+06

You need to join the Bangladesh Olympiad in Informatics Training Group (as Participant) to participate in the contest. You'll get full feedback about the tests, However, Codeforces currently doesn't show subtasks separately, also doesn't show points appropriately for single test. Hope you'll cope with the judging system.

Let's discuss the problems here after the contest ends.

Note: We created this contest for our own training, so we will be participating too.

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By Rezwan.Arefin01, history, 19 months ago, In English,

In polygon while setting groups and points I am facing this issue —

The form seems broken. Even though I added groups for tests, but they aren't being shown in the "Groups points policy and dependencies" form.
Also, "Set group" button is not working as expected. After clicking "Set group" nothing happens, but when I reload page then it shows that group is set, and when I select multiple tests and use "Set group" it only sets for one test. Also when I manually add test with that "Add Test" and assign a group, it is not working. But everything works as expected with points.

Is anyone else facing this problem? What's the workaround?

(I am using Firefox 60.0.2 on Manjaro 17.1.10)

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By Rezwan.Arefin01, history, 23 months ago, In English,

Me submission (others too) is in queue for ~5 hours. Is this the record?

Now it is 22:00, i submitted at 17:27. Still in queue :(

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By Rezwan.Arefin01, history, 3 years ago, In English,

In past few months, I solved 4-5 problems in live contests. Where the problem reduces to check if every number in a range occurs even number of times. I first mapped the values into arbitrary large random numbers and then used range XOR to determine if all them occurred even number of times.

After contest, I've heard that such solution using range XOR can be hacked using Gaussian Elimination. Can someone please explain me the process? I know Gaussian Elimination, but can't figure this out.

[I've heard that this problem — Check if all every number is a range has even frequency — can be solved by polynomial hashing too. Can someone explain that? Also is there any deterministic solution not using MO's algo?]

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By Rezwan.Arefin01, history, 3 years ago, In English,

Bangladesh Informatics Olympiad 2016 took place in 24th December, 2015.
The problems are now added in GYM — Bangladesh Olympiad in Informatics 2016 by rubabredWAn The problems are pretty interesting. Those who are preparing for IOI should give a try.
If interested the standings of the main contest can be found here — BdOI 2016 Standings

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By Rezwan.Arefin01, history, 3 years ago, In English,

Codeforces Becoming Boring ...

The judging system is becoming very very slow... :(

After submitting a solution ... We get the verdict at least after 30 minutes... even 1 hour... :( Every Time there is at LEAST 500+ submissions in the Queue.....

Who want to wait this long time to receive the Verdict ??

Cant there be a more faster judging system ? ! :(

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