Nothing pleases us more than making learning to program fun for you. One such opportunity came our way when we met Vinit at the ACM-ICPC World Finals in Phuket, Thailand. Vinit Shah had given a passionate presentation of his platform called uDebug, which was an unknown entity to us until then.
We instantly liked uDebug as we had been wanting to provide something similar to our users but were unable to take it up. One of the objectives of uDebug is to help you debug your solutions by suggesting input test cases of a problem for which the system will show you the output of a solution that’s been deemed “accepted”. Which certainly makes debugging a lot of fun. For us, it can also serve to strengthen the test cases for problems which may have weak test data. There have been incidents in the past where users have reported weak test cases for our problems but there has been no mechanism to validate and get them added.
We instantly discussed a possible collaboration between CodeChef and uDebug by providing users an interface (https://www.udebug.com/) to challenge the test cases for CodeChef’s problems. It meant that now you will have the power to test any problem of CodeChef against your test cases and if the community agrees with you, you can get them added on CodeChef.
It gives us immense pleasure to announce that you can now try your test cases for CodeChef problems on uDebug.
What it means for you as a user is:
We have added problems from our practice section (excluding the Beginner and Peer section) to uDebug for you to try your test cases on. Feel free to go there and experiment with your test data and debug solutions to those problems that you have not been able to solve.
If your test cases pass and find enough love from the community, they will be added to the problems.
How do I report a weak test case?
If you discover that test cases for a problem on CodeChef is weak, add your suggested (stronger) test cases on uDebug and flag the problem.
If your suggested test cases gets enough up-votes from the community, just send them to us at: udebug@codechef.com
We will add those test cases to the problem.
That’s it.
And as always, there will be a reward waiting for you. What it will be, you will get to know when you report it.
We hope you enjoy playing around on uDebug and we look forward to a long and fruitful collaboration with them.
That will be all from us for now.
Happy Coding!
Regards,
Rudreshwar
It was around three years ago, when our team mate, Suraj, had asked us to implement an automated system of sending goodies. We were struggling to deliver the users their winnings on time and quite a few of them would never reach their intended users. Not responded emails, faulty stale addresses, goodies getting lost in transit and tracking issues; left us hassled. We altered processes, included more checkpoints, reached out to our users, but nothing seemed to work.
Quite naturally, we liked the suggestion. The idea was to switch from a “push the goodie” system to “pull the goodie” one. Let the responsibility of getting a goodie be given to the users. We realised this would solve additional problems too, like the same user getting the same goodie multiple times, by giving her more options of accumulating points and winning something of a higher value.
This year, our growing struggle made us pick this up as a gift to ourselves and our users, as we turned seven. In the summer, with our intern, Raju Varshney, putting his hands up, we finally decided to put an all out effort to get this out. While he took up the coding, the rest of us scampered around to get an exciting new list of goodies prepared. And eventually the new system got ready to be served.
However, one thing at CodeChef is that we are a team full of pranksters! We love playing pranks on each other and we thought this to be a great time to include our users. It was long back that we did something similar and since then we have hardly done anything that grave! And this provided us with the perfect opportunity. It also served us as an experiment.
While we implemented the new system, we also decided to change the goodies to those of no monetary value to be considered as a token of appreciation for the effort put by the users. We wanted to see whether all our users want a goodie of monetary value or is it the winning that matters? We added three fun goodies on the site and kept our fingers crossed to see if one can spend her hard earned laddus against something that wasn’t initially promised – the duck, the cube and the ball.
And what we got was a pleasant surprise! Though we got a lot of criticism on the selection of our new goodies, we did find some of our users placing orders to actually get them! Kudos to them! Though we are removing those dummy goodies, we promise to give these users what they have ordered while reverting their laddus into their accounts. We had loads of fun and we hope that you would not mind this small prank of ours.
With this, we unveil the new goodie system. We have credited all your pending winnings as laddus into your account. Go ahead and check them out and have a look at the new goodies. And order whatever you like. We believe you will like some of them. In case you have any doubts or concerns regarding your laddus, do send us an email to laddus@codechef.com. Do not forget to read our terms and conditions to get more insight into the process and to not be disappointed later. We promise it is a good read.
Cheers,
Anup
It might be the last contest of the month, but our LunchTime is the one we anticipate the most, for it brings us the brightest young talent from schools across the globe. There have been many names that we have seen grow as a force to reckon with during the course of our LunchTime contests only and there are many others to look forward to. So, you see in addition to a great programming battle between the whizz-kids, some exciting problems, and an action packed Saturday evening, there is a lot to look forward to when it comes to our LunchTime contests.
And the August LunchTime 2016 was no exception. With Sergey Kulik, Shah Harshil Ketankumar, and Pawel Kacprzak on the problem setting panel, we were assured of a high-octane contest, with plenty of exciting battle for the top spot. And the competition was not only fierce on the schools rank table; even the general rank table saw a lot of action. Let’s start with the main rank table.
The fight to the top here was between someone who we have seen come through ranks and attain the status of pretty much a legend now, and the established legends of CodeChef rank tables. We are talking about rajat1603, who recently joined Chennai Mathematical Institute and is n more a school student and the likes of anta0, acmonster, uwi and others. We have seen Rajat win a Cook-Off while being in school, so it was not so much of a surprise than a treat to watch. And it always is, when you see someone grow in stature in such a short span of time. Rajat started strongly with ALPHABET, which he solved in the first 5 minutes of the contest, following it up with TREEDIAM in the 26th minute. However, LFSTACK and AVGSHORT troubled him a bit, with AVGSHORT taking maximum submissions for the green tick. As oppose to Rajat, anta0 got all his four problems in four straight submissions, and secured the top spot on the rank table.
On scene on the schools rank table was not all that different either with nano_ape of Shantou Jinshan High School, battling with the LunchTime debutant shivam312 of Delhi Public School, Rohini. And while nano_ape took six submissions to reach the top, shivam312 showed some great persistence for his three problems and took home the second spot in his debut LunchTime. There were few other names too that caught our attention and to tell you all of them, let us take you to the rank table of our August LunchTime 2016.
We start with the ROW top 10:
And now the Indian top 10:
Kudos, To all our young geniuses on their performance into the contest!
Before we move forward let us give you the final figures from the contest. The numbers from the contest:
And now, it’s editorial time. We hope you already have gone through, but with the ACM ICPC 2016 – 2017 season ahead, should you need to polish your strengths and concepts, here they are for you.
That brings us to the final segment of the post. We hope you enjoyed it as much as you enjoyed the problems from the contest. If you have anything for us, you know where to reach us.
With that, we will wrap us this post. Thanks for being with us through the post and through the contest. We will soon start publishing the posts from the September contests, so keep reading. And with ACM ICPC 2016 – 2017 starting, we will have many interesting tales to tell and if you have a tale, you can always reach us and we would publish it here.
Till next time, adios.
See you at the contests.
- Rudreshwar
Team CodeChef
When we sat down for the August Cook-Off 2016, the Rio 2016 Olympics were in their final days, and the Olympics of programming i.e. the ACM ICPC were fast approaching. Everyone was geared up to put their best foot forward, be it the sportsmen competing in Rio, or the young programmers around the world sprinting towards the ACM ICPC 2016 – 2017 regionals. We too were getting into the Olympic spirit and getting right behind our favorite sportsmen and you all, our favorite programmers. While the constant support messages and the eventual cheer went out on the social streams, we had our August Cook-Off 2016 well and ready for you all to come and showcase your brilliance. And it gives us immense pleasure to say that, we weren’t disappointed.
The problems of Alei Reyes presented the participants with a great challenge, which they all embraced. However, the start of the contest was not as expected for many of the early birds. Unlike some of the previous Cook-Offs where it was a green tick galore in the early stages, we saw only 7 of those green ticks in the first 50 submissions into the contest. We got 5 more in the next 50, but by now, the dreaded red cross of WA had taken over the submission table. It made us think if everything was alright with the problems, and it was. Our tester Hasan Jaddouh had done a great job testing the problems leaving nothing to be questioned about. And we could have been happier.
The first problems to have received submissions in the early stages of the contest were ALICE and TWEED. And while TWEED, turned out to be an easy nut to crack, ALICE stood exactly at the opposite end of the difficulty spectrum. How difficult it was? Well, out of the 200 submissions that it got, there only were 3 ACs. While, that might sound a tad too difficult, the other problems were not all that easy as well. We had 35 AC out of 300 submissions for MADHAT, 15 out of 150 for MCKTUR, and 9 out of 100 for QUEHEA. And with the busy competitive programming season ahead, we think it would have given a good practice ground to everyone who participated in the contest. But we still would like to hear from you, what you thought of the problem set, were they a tad too hard for your taste, or they were just as you like the problems to be.
Now, let us take a stroll through the rank tables to meet our winners:
We start with the ROW top 10:
Now, the Indian top 10:
A big round of applauds to all our winners and to you all for competing in the August Cook-Off 2016.
Now, it’s editorial time. Penned by our omnipresent admin Praveen Dhinwa, the editorials will help you understand your mistakes during the contest if there were any. If there were not, you still might want to have a look at them to better prepare for the upcoming ACM ICPC season.
And that will be all from us here at CodeChef. We hope we were able to cover the contest along with all its highlights. However, if we have missed out on any, feel free to let us know. You can write to us, call us, or send us a message on social streams. We love hearing you guys.
We will come soon with the final tale from the August contest, i.e. the August LunchTime 2016, but till then, keep coding.
See you at the contests.
- Rudreshwar
Team CodeChef
With August we go one step closer to a rather packed programming season. For the school students, we have the ZCO/ZIO, which for the college students have the ACM ICPC regionals fast approaching. Now, with so many significant competition lined up, programmers seek every opportunity they can get to test their preparations. And in August Challenge 2016 we presented them with one.
The problem set for August Challenge 2016 was nicely spread on the difficulty spectrum. While Chef and Chocolate made life easier in the contest, Chef and Guard Towers presented a stern test to everyone. However, the participants seemed to be enjoying the problems at both the ends of difficulty level. How do we know that? Well, the number of submissions on each of the problem tells us so.
Now, while the problem set was nicely balanced, the competition on the rank table was pretty unpredictable. The battle between the newcomer alladdin and the seasoned ceilks made up for an exciting battle to witness, with the eventual emergence of anta0, skyfire, and rns4 keeping us all on the edge of our seats. We are sure that the participants would have enjoyed the battle even more. Now, to find out who emerged on top at the end of the contest, let us take you through that rank table to meet all our winners.
First, the girls:
Now, the ROW top 10:
Now, the Indian top 20:
Now, we move to schools:
ROW Top 5:
Indian top 5:
And finally we move towards the special achievers category with users having highest scores for the challenge problem, other than the winners:
First the ROW top 3:
Now, the Indian top 3:
A huge round of applauds to all our winners and to everyone who took part in the contest. Now, before we move forward, let us give you the final stats for the contest.
And finally, let us take you to the editorials for the contest.
We hope you enjoyed the contest. And before we put full stop on this tale of August Challenge 2016, let us thank our problem setters Vitalij Kozhukhivskij, Dmytro Berezin, Vasya Antoniuk, Nazarbek Altybay, Rishabh Jain, Kevin Charles Atienza, Shah Harshil Ketankumar, Snigdha Chandan, and Misha Chorniy, our tester Sergey Kulik and the entire panel for creating such a crunchy contest.
That will be all from us. We will soon come back with the stories from the two remaining contests from August. Till then, keep coding and do let us know your thoughts on the contest, the post, or just anything in general.
See you at the contests.
- Rudreshwar
Team CodeChef
SPOJ will be migrating CodeChef Judge to new servers today at 21:30(IST). This will be a quick migration and we will require a submission downtime of 15 mins. We will stop submissions after 21:30 for 15 minutes.
SPOJ will also be moving away from their current server and ISP, to a new server room and cloud. This will not affect the workings of the site in anyway.
Here’s everything you need to know about the entire migration.
You will not be able to make submissions into the ongoing August Challenge 2016 for 15 minutes starting 21:30 IST on 9th August 2016 to 21:45 IST on 9th August 2016.
The new judge servers are around 30-32% faster than the previous ones, hence, there will be some inconsistency in the execution time for the submissions made after the migration. However, you do not have to worry about the inconsistency as we will be re-judging all the submissions that ran on the old server at the end of August Challenge 2016.
That will be all for us. Should you have any questions or concerns, feel free to get in touch with us.
Rudreshwar,
Team CodeChef
July perhaps was the best month in the first half of the year. We started the month on 1st of July with July Challenge 2016, followed by the SnackDown 2016 Finals, Cook-Off, and finally everything culminating on the July LunchTime 2016 on the 31st July, 2016. In between there were many other challenges spread here and there, and we are sure you would have enjoyed each one of them. Now, we have already told the tales from the Challenge and Cook-Off, so it’s time now to revisit the LunchTime. So, shall we?
Created by an all Indian and rather young problem setting panel featuring Praveen Dhinwa, Animesh Fatehpuria, and Pushkar Mishra in company with our translation team including Hu Zecong, VNOI Team, and Vasya Antoniuk, the July LunchTime 2016 was all set to give an exciting farewell to July with its four fiery problems. That is not to say that they weren’t fun. With the names like Drumpf for President! and So Close Yet So Far the problems caught immediate attention of the participants, with the former getting the most of it. True to its name, So Close Yet So Far proved to be a tough nut to crack, with only 12 submissions out of the 900 on it getting the sweet green tick of happiness.
Now, our LunchTime contests have been a smooth affair, just like a flag-to-flag race. And we can say that for most of them. However, it wasn’t the case with July LunchTime 2016. However, the issue this time, was the time limit of CLOSEFAR, which was a tad on the higher side. It resulted in submissions taking longer than expected to execute and consequently the prolonged delay in getting the results for the submissions. As a result, we had to change the time limit for the problem twice, during the contest and had to extend the contest by 1 hour. So, the participants got 1 more hour to play with the problems.
All those issues had no effect on the proceedings on the rank table though. For the very first time an Indian school student was emerging atop the global rank table. And it was rajat1603. No surprises there. rajat1603 has gone from strength to strength with every passing contest and it was just one of his vintage performances. The other LunchTime legends including aktl, fleimgruber, and vladik were all present right at the top of the rank table. But with a margin of 50 points rajat1603 took home the July LunchTime 2016.
Who else stood where? Lets find it out through our rank list.
First, we have ROW top 10:
Now, the Indian top 10:
After the rank list let’s have a walk through the editorials, which we are sure you must have enjoyed as much as the problems. So, here they are once again for you:
And that will be it, from the July LunchTime 2016. We now move towards August contests and will try and serve them soon.
Till then, do let us know your thoughts on the problems, the contest, and this post. You can send them to us at feedback@codechef.com or can post them straight on the comment section below. We love reading them all.
That will be all from us for now.
See you at the contests.
- Rudreshwar
Team CodeChef
Here are all the video lectures from the Indian Programming Camp 2016.
Enjoy the lectures and share them among your friends and families.
Rudreshwar
Team CodeChef
Coming to July Cook-Off 2016, we were a bit relaxed and rejuvenated. We had just wrapped SnackDown 2016 amid great joy and fervor. The big SnackDown 2016 Final was behind us and life was taking its sweet time to return to routine. Thanks to a couple of week’s gap between the July Challenge 2016, we had the luxury to afford that time. So, we spent some time wrapping up the post SnackDown work and some to get the July Cook-Off 2016 ready for you. Thanks to the awesome problem setting panel featuring Misha Chorniy, Pushkar Mishra, and Karan Aggarwal as the setter, tester, and editorialist respectively, Praveen Dhinwa, the contest admin, and our team of Translators Hu Zecong (Mandarin), Team VNOI (Vietnamese), and Sergey Kulik (Russian), we did not have too much to do.
The problems for the contest were evenly spread across the difficulty spectrum, which means that there was something for everyone into the contest. While Chef and Proportion required users to help the chef in figuring out some proportion, the Chef and Sort asked them to find the expected value of findSwaps function. And while a majority of participants had success with the proportions, finding the expected value of findSwaps function kept them on the edge of their seats.
While the aforementioned two problems were on the contrasting ends of the spectrum with Chef and Proportion being the easiest of them all, we did have Chef and Numbers, Chef and Land, and Chef and Array making life a little easier for the participants. And we think everyone enjoyed them too. At least that’s what close to 10K submissions in 2.5 hours duration of contest suggests. However, we would like to hear your thoughts on the problems, how did you find them? Do let us know in the comments section.
With everyone enjoying the problems, the attention now moved to the rank table. After the blistering performance from rajat1603 in June Cook-Off 2016, we were excited to see what July Cook-Off 2016 has in store for us. Thanks to the debutant ikatanic and um_nik.
While ikatanic was making a return to CodeChef after a prolonged absence, for um_nik, it was the very first contest. However, it’s worth mentioning that it was the first Cook-Off for both of them, so, it’s safe to call them Cook-Off debutants. And what a debut it was. Emerging atop the mmaxio, raveman, al13n, xellos0, and the likes certainly isn’t an easy feat to achieve. And after what we have seen in July Cook-Off, we can’t wait to see them repeat in many of our contests. We think this was one of the best debuts in our Cook-Off’s. If you know of any others, do let us know in the comments section.
With that let’s have a look at the rank table to see who all accompanied our dynamic debutants.
We start with ROW top 10:
And now the Indian top 5:
While the ROW rank list had some big debuts, the Indian rank table to presented a beautiful sight with anudeep2011, djdolls, and rajat1603 occupying the podium. Those are the names that we have been hearing for a long time and certainly will be hearing a lot in the years to come.
And on that beautiful note, let’s move towards the final segment of the post. It’s time for the editorials.
With that, we would like to take your leave for now. We hope you enjoyed the post and that we have been able to cover most of the highlights for the contest. However, if you still think that we have missed any, feel free to let us know through your comments, emails, or through any mode you like. You know how to reach us. 
Until next time, keep coding.
See you at the contests.
- Rudreshwar
Lecture 1: Sqrt decomposition, By Sergey Kulik
Slides
Lecture 2: Dynamic connectivity problems and their applications, By Sergey Kulik
Lecture 3: Chinese Remainder Theorem, By Praveen Dhinwa
Lecture 4: Introduction of Algebra, By Kevin Charles Atienza
Slides can be found here
Lecture 5: Mobius inversion and related sums, By Kevin Charles Atienza
Slides can be found here
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