Saturday, October 26, 2019

A past glory week

TopCoder Open 2019 Round 2A was the first round of the May 20 - May 26 week (problems, results, top 5 on the left, parallel round resultsmy screencast). It was the first time everybody except the three stage winners and 30 Round 4 qualifiers from the SRM stages could compete, nevertheless the top 3 was taken by participants who did not participate in SRMs at all for 6+ months and just came back for the TCO. Congratulations to them and to everybody else who made it to Round 3!

Open Cup 2018-19 Grand Prix of Ural took place on Sunday (results, top 5 on the left). Four teams solved everything, albeit with quite a variety in the number of incorrect attempts :) Congratulations to team Past Glory on the win!

Problem J required a nice but not very difficult observation. You have n (n<=50) cells arranged in a circle and a token in one of the cells. Then you repeatedly do the following: pick a number uniformly at random from the set {-2,-1,+1,+2}, and move the token this many cells along the circle (positive numbers corresponding to the clockwise movement, and negative to the counter-clockwise one). What is the expected number of moves before the token visits the same cell twice? The cells that are passed through in the middle of a -2/+2 move do not count as being visited.

This round wrapped up the Open Cup 2018-19 season, pending the onsite finals in August in Petrozavodsk (overall results, top 5 on the left). With 20 rounds, this season was the biggest to date, and the round creep is not unlike what happens in the other Grand Prix-based competition, Formula 1 :) Congratulations to the top teams, and I'm especially glad to see that the geography of the top of the standings is expanding further. Here's hoping that the next season has even more stronger teams and less rounds :P

Finally, Codeforces Round 562 followed later on Sunday (problems, results, top 5 on the left, analysis). The mysterious user Vn_nV took the first place and was the only contestant to solve all problems. Well done!

Thanks for reading, and check back for more!

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