long one-liner which is not that easy to read. this good too

Works since Java 16. This solution was written in 2018 when we only had Java 8.

tacticalcacti, use spoiler flag next time, please.

Could anyone break down this regular expresion please.

note: the bitwise operator allows to not use parentheses for the previous operation (which would become required when using the usual/dedicated operator to achieve the same logic without the bitwise stuff).

PS: don't forget the spoiler flag, plz (comments are visible from the dashboard)

thanks, added fix to translation to that one instead: https://www.codewars.com/kata/543ddf69386034670d000c7d.

Not a kata issue.

It is mentioned as feet per hour.

Read the description

If the array of arrays is null/nil or empty, the method should return 0.

the last array is empty so you have to return 0

yes.

To return a copy, so that the user getting that list cannot mess with the internals of the Warrior instance (but that code is bad, to achieve that purpose, I don't know why I wrote it that way... Look at the fork, it's far better)