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### rng_58's blog

By rng_58, history, 14 months ago, ,

CODE FESTIVAL 2017 Qualification Round C will be held on Sunday (time). The writers are sugim48 and wo_.

Contest Announcement will be posted later.

This is one of the three qualification rounds of CODE FESTIVAL. In total, 20 foreign students will qualify in three rounds (Check the official site for detailed rules). If you are eligible for the onsite contest, please don't forget to fill the form at https://krs.bz/rhd-itm/m/codefes2017_en. Please check the detail of the tournament at http://codeforces.com/blog/entry/53502.

The contest duration is 2 hours, and there will be 6 problems. The first 4 problems are mainly used for choosing domestic students and much easier than other tournament competitions. However, we added two more problems and we hope these are interesting and challenging enough for choosing 20 qualifiers. Note that there is no time penalty for incorrect submissions. The time penalty is MAX, not SUM.

The point values are 100 — 200 — 400 — 700 — 1600 — 1800. If you are unfamiliar with AtCoder System, 2X-point problem in AtCoder is as hard as TopCoder's d1 X-point problem.

Let's discuss problems after the contest.

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 » 14 months ago, # |   +22 Reminder: The round starts in 24 hours.
•  » » 14 months ago, # ^ |   +23 Reminder: The round starts in 1 hour.
 » 14 months ago, # |   +78 Tokyo! Tokyo! Tokyo! ヾ(≧▽≦*)o
 » 14 months ago, # |   +45 As always, hard problems were great :).
 » 14 months ago, # |   +15 Why does wire penetrate exactly A + B + C — 2 blocks (problem E)? Can someone please tell me the proof?
•  » » 14 months ago, # ^ |   +23 Because gcd(A, B) = gcd(B, C) = gcd(A, C) = 1, the wire will never pass through one of the vertices or edges of the cubes, except the start and the end.Basically, if you trace the position of the wire and look at it's position (x, y, z). Every time one of ⌊ x⌋, ⌊ y⌋, ⌊ z⌋ change, it means you've hit a new cube. Because they can't increase at the same time (see the argument above), and we have A - 1 changes on x direction, B - 1 and C - 1 changes on the y and z, plus the cube from the beginning, we'll hit exactly A - 1 + B - 1 + C - 1 + 1 = A + B + C - 2 cubes.
•  » » » 14 months ago, # ^ |   +15 Thank you very much. That is a very nice proof.
 » 14 months ago, # |   +10 Can someone please provide any hack for this submission
•  » » 14 months ago, # ^ |   +8 Good day to you,Try eohqetj .. imho the answer shall be 7 (is that right?)Good Luck & Have Nice Day
•  » » » 14 months ago, # ^ |   +19 Awesome. Thanks and Good Luck! :)