Hey you who is trying to solve this, non spoiler-ish tips:

• you gotta know a math trick
• write equality on paper, and do some algebra.

both tips are unrelated.

Well, thank you for reminding me that basic advice, turned out that was super easy after all.

look more carefuly at the description : it mentions the method getNext() to get the next node. So, in order to get the next node, you can do node = node.getNext().

the node object is given as an argument, and is an instance of a custom class defined somewhere else.
As the challenge require you don't modify these, it does not really matter what its implementation is.

Best solution by far, as far as I can tell, the only one worthy of production : readable, no loop, shortly and well documented.

You'd gain vertical space and a bit of performance by using list comprehensions. Also, you could treat directly array1 and array2 without any intermediary variables

cheer :)