The December Long Challenge 2020 was nothing short of an eye-opener for people who think that programming cannot get highly intense. With so many people going for the top spot, it was undoubtedly one of the most enjoyable and competitive contests in recent memory. Without any further ado, let’s get started with all the highlights from the contest.

**Where do our programming heroes stand this time?**

If you followed the contest on our social media handles, you might be aware of what an incredibly exciting long challenge this has been. Let’s start with all the action that took place in Division 1.

The fight for the throne in Division 1 reached a whole new level this time, with an 18-way tie for the first position. The major winners from those 18 programmers were maroonrk, and krijgertje as both of them jumped stars from 4 to 5. After taking a break during the November Long Challenge 2020, ACRush was again back on top with a rating increase of 57. tmyklebu and progmatic also stayed atop the rank list mirroring their performance in the October Long Challenge. rns6 continued his streak in the long challenge with a rating increase of 153. The veterans endagorion, mcubedev, oilhun and ryodan were also part of the top position with an increase in rating of 136, 142, 153 and 133 respectively.

We had two Indian coders making it big this time around as Google’s djdolls and sg1729 from IIT Bhubaneswar claimed the top spot with a rating increase of 142 and 147 points respectively. djdolls made his comeback to competitive programming after a gap of three years and got the gold in his very first contest on his return. He took his points tally to 2386. sg1729 had a decent November Long Challenge 2020, but he went for gold this time taking his total to 2428. For the complete rank list of Div 1, click here.

Chinese programmers completely dominated the crest in Division 2. We had a 3-way tie for gold, all between coders from China. jiangly, rgb_icpc9 and yuyue all grabbed the pinnacle with jiangly jumping from 3 to 4 stars and the other two from 1 to 3 stars. The fourth position was again booked by a Chinese coder xyrno1 who jumped from 1 to 3 stars with an increase in rating of 275. Next, we had the American coder mearnest who went from 3 to 4 stars with an increase in rating of 184. There were a total of 3 Indian coders in the top 10 of Div 2. dishantpawar95 and dragno99 shared the seventh position while compatriot gagan_sharma clinched the ninth rank. A total of 19 Indian programmers made it into the top 25 of Div 2. For the complete rank list, click here.

**Problems that keep your head spinning around!**

When we think about the long challenge, the first thought that crosses our minds is the sheer number of problems that the coders need to face for ten days. With this being the last Long Challenge of the year, let’s see how things panned out for our programmers with the problems this time.

As the rank list suggests, Division 1 was highly competitive, and the same goes for the problems as well. The division had ten questions, one more than it was during the November Long Challenge 2020. The favorite problem across Div 1 was certainly Even Pair Sum with 1240 submissions having an accuracy of 78.34. Positive Prefixes was another problem that pondered to the Div 1 coders with 1197 successful submissions. But not everything was a piece of cake for the Div 1 participants as the problem Palindromic Equivalence received only 18 successful submissions in ten days. Digit Matrix and Linear Combination were some other problems that caused headaches for the coders. In total, we received around 28488 submissions from 1272 users in Div 1.

Division 2 also had ten problems, but the number of submissions was exponentially more than Div 1. The problem Vaccine Production had by far the most successful submissions with 19150 and an accuracy of 31.67. Even Pair Sum came in close with 18898 successful submissions. If you go by the numbers, the tricky problems in Div 2 seemed to be even more menacing for the coders. Digit Matrix, Linear Combination, and Permutations just had 5, 6, and 7 submissions respectively. Div 2 received a total of 360444 submissions from 24048 users.

**A word with the problem setter.**

We got in touch with the problem setter for Square Root of LCA Convolution (LCASQRT), Ivan and asked about how he came up with such an intricate problem and what was the inspiration behind it.

“I thought about some convolutions, that can be. There are many well-known convolutions; each of them uses some operation. Like convolution with sum is known as multiply of polynomials; also there are or, and, xor convolutions, that are well-known too. I thought about other operations and what are the convolutions for them. When I thought about the LCA operation, I found that the convolution is pretty and started thinking about the problems related to it. That is how I developed my problem.”

When asked about what sort of performance did he expect from the coders for his problem, he said,

“I expected this as a medium problem, so I think it would be from 4th to 6th among all problems sorted by the hardest. I can say that my problem is a bit educational because after making the first step with convolution, you should find square roots by modulo, and there exists a well-known algorithm for that. But this problem is a perfect opportunity to recall this algorithm.”

Given the number of successful submissions that the problem received, it certainly caused a lot of trouble for the coders out there.

Such an intense contest like the December Long Challenge 2020 happens once in a while, and we enjoyed every bit of it. We hope that you enjoyed it too, and the intensity would encourage you to be a part of the upcoming contests. If you want to go through the highlights of November Long Challenge 2020, click here. This is Ashutosh signing off till then keep coding and prepare yourself for the forthcoming coding challenge!