Fix the app
Proof reading required
1. Occasionally unclear language describing the test to be resolved.
2. Several typos in the solution (use of a single colon rather than double colons pointing to std namespace)
3. Rejected solutions that are perfectly viable but may, for example use optional parentheses for clarity. I ran several of my solutions in Visual Studio and they worked fine but we're deemed wrong in the app.
Just needs a good dose of proof reading and some flexibility in the answer evaluation logic to really raise the value of the app.