I want to point out that, just like in real life, its the inclusion of that "++" which complicates things. Without them, it would be straightforward and elegant, having only 1 logical solution.

Makes you wonder why people keep insisting on having the "++" around. Why not ditch them and go back to basics.

C++ programmers always let their friends access their private members, so ...

Judging from how it feels to write the language, it's definitely number 2.

There's some joke about pointers here that I'm not C++ savvy enough to make.
I'll let you workshop it.