If you can't tell the difference between sketched-out kinda sorta pseudocode and potentially workable C++ then you're certainly not competent in C++.

And if you fail to communicate the requirement for one or the other then you're certainly not a competent interviewer.

You also have to ask what exactly is being tested here? Is it the ability to remember syntax? To remember an algorithm? To improvise an algorithm? To recognise which algorithm is needed?

What, exactly?