Missing a picture for the n = 3 example!

Would you please be so kind to tell if (and how) this kata conforms to this point of authoring guidelines?

Do not use problems from other sites, unless it's allowed by that site's licensing policy and/or terms of use. Explicitly give appropriate credit if your kata is based on, or inspired by, someone else's work.

For the record: original problem is problem G in this set.

Or for olympiad for 13-year-old codes - it's taken from this year Ukrainian Olympiad of Informatics, 2nd stage (1st - school, 2nd - town, 3rd - region, 4th - republic stage). Pupils 7-11 grade take part, it means participants are 12-17-year-old. I proposed 6 kyu, please propose your own level :)

Nice kata! I really enjoyed it, but was looking for an olympiad for 63-year-old coders :-)

Reduced number of tests (it was 100) and now tests load takes 1.3 sec and tests load plus solution takes 1.6 sec

Tests are too heavy. An empty solution takes already 4 seconds to load.

Yep, in the tree that is described even in the example, this solution returns the incorrect value "15" instead of "-51".

Neat. I never knew that Python allows one line for conditional: resulting statement

I was wrong. Sorry

WRONG! Check "with your hands on paper" for n = 9. You cannot build 51 hexagons on 81 triangles! Only 49.

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Thank you and yes I understood it enough to solve the problem now. Super cool!

Added. Hope this will be understandable