## Saturday, October 12, 2019

### A null week

Long time no see :)

The Apr 29 - May 5 week had a lot of rounds, starting with Codeforces Round 556 on Monday (problems, results, top 5 on the left, analysis). Just two contestants solved everything, but Um_nik got ahead of other top finishers by solving problem C much faster. Well done!

TopCoder SRM 757 followed early on Tuesday (problems, results, top 5 on the left). This round wrapped up the selection of the third direct TCO19 finalist, and rng_58 has won this honor very convincingly (link, click on "Stage 3"). As for the round itself, ksun48 was the only contestant to solve everything, and even -50 during the challenge phase did not affect his result. Congratulations on the victory!

TCO19 Round 1B on Wednesday selected the final 247 participants of Round 2 (problems, results, top 5 on the left, parallel round results). Even though 750 contestants could advance, only 247 have managed to get a positive score. Just like in Round 1A, the challenge phase was vital to get the first place. Congratulations to homo_sapiens!

Google Code Jam 2019 Round 1C on Saturday was also the last Round 1, this time with 1500 final spots for Round 2 up for grabs (problems, results, top 5 on the left). logicmachine was 4 minutes faster than the competition, and qualified to the Round 2 in style :) Well done!

AtCoder Grand Contest 033 also took place on Saturday (problems, results, top 5 on the left, my screencastanalysis). tourist has produced another dominating performance and completed all problems a good half an hour faster than everybody else — a super impressive result!

Problem C was a bit standard but still cute: two players are playing a game on a tree with 200000 vertices. The players make alternating turns, in one turn a player can choose any vertex as the root of the tree, and then all leaves of the resulting rooted tree are removed (or the root itself if it's the only remaining vertex). The player who has to move after the last vertex has been removed loses the game. Who will win if both players play optimally?

Codeforces Round 557 also happened on Saturday (problems, results, top 5 on the left, onsite round results, analysis). Benq was just a tiny bit faster overall, and has also protected his problem solving highest score with a successful challenge. Congratulations on the first place!

Problem E was of the constructive kind, and I tend to enjoy those disproportionately :) There are n coins of three different colors, but you don't know which color each coin has. In order to determine that, you have 7 rounds available. In one round, you can choose an arbitrary set of non-intersecting pairs of coins, and you will be told whether the coins in each pair are of the same color or not. After the 7 rounds you need to separate all coins into three groups by color. Can you see how to do it?

Finally, Open Cup 2018-19 Grand Prix of Daejeon wrapped up the week on Sunday (results, top 5 on the left). Team MIT NULL has won this time in large part thanks to having just one incorrect attempt, compared to 18 for the World Champion team Red Panda in the second place :) Jumping a bit into the present, 2/3 of that team together with Scott Wu have joined the ranks of other veteran teams like ours for the 2019-20 Open Cup season — always great to see strong teams sticking around after their second ICPC World Finals!

Thanks for reading, and check back for more as I hope to climb back into the present soon :)