Any idea why removing trailing space from my solution gives me this:

Expected: equal to "20 8 5 14 1 18 23 8 1 12 2 1 3 15 14 19 1 20 13 9 4 14 9 7 8 20"
Actual: "20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 1120 8 5 14 1 18 23 8 1 12 2 1 3 15 14 19 1 20 13 9 4 14 9 7 8 20"

It's like it pulls entire 2nd string from somewhere and places it in front of my own. It isn't there before i try using pop_back or anything else.

Took me days to solve it, as it was pretty much my first contact with regular expressions. Solution came out a bit messy as a result, but at least it was a good learning experience. Great kata overall.

I was confused by the notation myself but its just what it says, a prime factors decomposition. Lets take example from description: 86240=2^5x5x7^2x11