Hilarious

How so? Integer multiplication and division by two are internally realized using bit shifts:

x * 2 == x << 1
x // 2 == x >> 1

Which of these is better? (In my own experiments, I found only a negligible speed difference < 1%)

Well, I see lots of rng.nextInt in the test case generator function... Where is your assertion based upon?

You wrote "i < 99999" -- note that 99999 is a perfectly valid pin ;-)

Why the ^ and the spaces in your RegExp?

Beautifully compact code, but please note that you compute the same product nums.length times... Better precompute it in the way of javier-elizaga.

Not the most concise option (like those nifty regexes), but certainly best practice for both readability and performance. Good job!