Same thing, I have 8s runtime, but none complex tests passed. It seems this issue will never be fixed as one can find this kind of reports in a lot of katas in relation to C++ solutions.
In this case it seems even the type in Equals that is created by the test itself fails.

It would be better if there were specified limits for m and n, in C++ arguments are long long and that's quite a large limit. With my current solution I get around 8s for [1, 1000000] range and this passes the tests, but it would be more useful to have input range and time limits specified as a hint from beginning. In other systems similar to codewars when I see specific range and time limit I get an idea of what direction I should take (in some systems there is even specified desired complexity), thus if a simpler solution will suffice or I need to come up with a more complex one without wasting time on trying this out with tests.