"I don't" :D

std::vector< std::vector< int > > combinations;

This can be a memory hog in larger projects. Thankfully we don't need to store these roads for future. :)

I like solutions like these, because they are the closest to how I did it, but they are better in some way or another. I created a whole vector of numbers that contain a given digit... Now I know there was no use for it :p

I have never seen "while(runs --> 0)" before :o How does it work? Is it just a post incrementation combined with comparison?

This shouldn't work for huge numbers. Unfortunatelly there's no test written for that, but imagine 1000 digit number. There's a reason why is it passed as std::string.

I read it ;)

One can further improve this by not creating second if-statement. If you sum negatives and add 0 to them, it doesn't affect the sum. Thanks for teaching these temporary vectors :)

"How to kill a fly with a cannon" :D