Category Archives: Editorialist

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January Lunchtime 2016 on CodeChef

January Lunchtime 2016 has just finished. The problems used there are so great, that I have to let you know about them! 

The most amazing problem in my opinion is the one involving Dilworth's Theorem, check it out: Table Covering

I wrote all editorials to the problems, they are very descriptive and detailed and are available here: editorials.


Invitation to India Hacks 2015, Qualification Round 3


I want to invite all of you to participate in the last Qualification Round of India Hacks 2016, which is organized by HackerEarth.

This is the third and the last one qualification round. If you missed or didn't qualify in the two previous rounds, this is the last change to advance to the semifinals.

Qualification Round 3 takes place on January 17, 04:30 PM CET (click to check your timezone). Top 1000 participants with non-zero score will advance to the main contest.

The prizes in India Hacks are quite nice, including a trip to San Francisco, many tech gadgets and a lot of goodies for top 50 participants. If you want to grab any of them, or you just like to compete agains a lot of other programmers and you haven't qualified to the main contest yet, reserve a time slot for this round!

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I'm a tester of the problem set and a conductor of the contest. There will be 5 problems in the contest and you'll have 3 hours to solve all of them. In addition, a partial scoring system will be used in all of them, which means that you'll get points for each correctly solved test file in any problem.

Big thanks to tanujkhattar, subway, aditya1495 and hellgeek for creating the problems, to belowthebelt for technical assistance and to I_love_Tanya_Romanova and Errichto for proofreading and solving the problems, and for all their suggestions.

Since this is the last qualification round, problems won't be very hard, so if you're going to participate, you may assume that submission time might be a big factor in the final standings.

As a small hint, I can tell you that you should be prepared with number theory, computing optimal subsequences of some types, and techniques used with computation on trees.

Have fun and good luck to all of you!

See you on the leaderboard, hopefully at the top of it :)

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December Easy 2015 by HackerEarth

Hi all,

December Easy Contest by HackerEarth is taking place on December the 3rd at 5:00pm CET. Contest duration is 3 hours.

There will be 5 problems to solve, all algorithmic ones, especially targeted for beginners. However, I'm pretty sure that any participant will find them interesting to solve :) All the problems have partial scoring and ties are resolved by penalty time.

A little hint for you, 3 of the 5 problems will ask you to minimize some value, so be better prepared with methods of solving these kind of problems :)

As the tester and editorialist for the contest, I want to thank the problem setter aditya1495 and admin belowthebelt for preparing the contest. It was nice to work with you guys as always!

As a tradition in Easy Contests, the top 5 beginners (1st year or 2nd year) will receive HackerEarth T-shirts.

Good luck and see you on leaderboard!

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November Easy on HackerEarth

On every 1st day of a month, HackerEarth hosts a special contest. It is called an Easy Contest, because it is targeted especially for beginners. However, it does not mean that there are just easy problems to solve, not at all!. This time, the problem set is prepared by shef_2318 and tested by Kmcode. I write editorials, as I usually do for this contest.

The contest is available here: November Easy 2015

There is something special about the contest. This time, problem set contains two unusual problems to solve. They are  completely different than any standard algorithmic problem, so we expect a very nice competition and we are curious how will participants deal with these problems. In addition to these special problems, you will get a chance to solve one problem defined on a tree, decide who has a winning strategy in a special game, and solve two problems targeted for beginners.

See you on leaderboard!


CodeChef October Lunchtime

October Lunchtime starts in just under 24 hours, and I am the editorialist for the whole contest.

This time, problems are especially interesting for me. Big thanks to Pavel Sheftelevich, who created all of them. Pavel has a great ability to create incredible problems with really simple statements - the thing we all love. The setter of a previous Lunchtime, Sergey Kulik, is the tester of the whole problem set this time. We started working on this contest later than usual, but it turned out, that a great contest can be prepared in just a few days :)

If you decide to participate, which you should do, you will probably start with solving two simple problems: an easy string problem and an interesting one ad-hoc problem related to multiplication extremely big numbers. For those of you who managed to solve them quickly, there are two harder problems waiting. I can tell you, that a desired solution to one of them uses a technique, which is not known as much as it should be. I will describe the approach with details, in the editorial, which will be posted just after the contest on Codechef discuss. The last subtask to the second of these harder problems, at first time might look unsolvable for some participants, but I really encourage all of you to engage all of your skills to solve it. If you manage it, you will be very pleased :)

See you on Leaderboard!

All editorials are available here