I would say that no, it's not idiomatic C++. There's no reason to use dynamic allocation for your vector<bool>, for one obvious example.

As for its being faster, yes, that's expected and fits well with previous tests.

If you care about speed, you could at least consider using operator[] instead of at. I rarely find at very useful, personally.

I'd advise against using std::endl as a general rules. If you just want a new-line, just write a new-line. If you want a new-line followed by a flush (which is what endl actually does) do that explicitly, such as std::cout << res << "\n" << std::flush;.

While res isn't exactly a terrible name, I think something more descriptive (e.g., result) would be better. If (for whatever reason) you're concerned about the length of the name, I'd consider using sum instead.

I would say that no, it's not idiomatic C++. There's no reason to use dynamic allocation for your vector<bool>, for one obvious example.

As for its being faster, yes, that's expected and fits well with previous tests.

If you care about speed, you could at least consider using operator[] instead of at. I rarely find at very useful, personally.

I'd advise against using std::endl as a general rules. If you just want a new-line, just write a new-line. If you want a new-line followed by a flush (which is what endl actually does) do that explicitly, such as std::cout << res << "\n" << std::flush;.

While res isn't exactly a terrible name, I think something more descriptive (e.g., result) would be better. If (for whatever reason) you're concerned about the length of the name, I'd consider using sum instead.