I clarified that they are full binary trees. Otherwise looks great. The tree prints look fine and are helpful on small cases.

While not breaking a particular implementation, it seems like multi-skill cycles don't make sense given the description. Especially with the one parent rule, unless they include zero.

Neat task.

AwesomeAD, It looks great! I made a few tweaks.

• Put description initial xs ys in code block
  to highlight and for easier matching with later results.
• Changed description example [10, 11, 12] to [11, 12, 13]
  as easier to follow against [1, 2, 3]. Also in Go.
• Added pub to the starter signature, pub fn foo().
  So far on CW, I've mostly seen fn foo(),
  but that just creates a Clippy unused warn if you copy paste to an IDE.
  Also to the provided solution for consistency.
  Its not needed by sub modules, like tests, but doesn't hurt them.

Varied token lengths would be nice. Plus that also really needs to be in the main description text, though editing that is more involved. A separate update for the main text makes sence.

  test('Apple1,Bag2,Cat3,Dolphin4,Eel5', 'Bag2 Cat3 Dolphin4');