The remove_char function was fun to write, and I found a bug in my first implementation!
The Intrusive Stack problem; however, is confusing to read. I searched for a description of what an intrusive stack is on DuckDuckGo, and the first result was for the Scalien job application. Further down on the page (through what appears to be several quasi-related links) I found a Boost article on intrusive containers which explained the idea much more clearly. After reading the Boost description, then re-reading the Scalien description another 3 or 4 times, I'm not comfortable to write an intrusive stack.
Are you sure applicants aren't failing because the application problem for the intrusive stack is written in a confusing manner?
"Are you sure applicants aren't failing because the application problem for the intrusive stack is written in a confusing manner?"
I don't know, its very possible. I found the application problem very easy to understand and writing an intrusive stack is really easy, so unless I'm very disconnected from the "average applicant", who apparently 1) isn't very good at C++ and 2) doesn't know how to implement common data structures, the problem must be with the application.
Are you sure applicants aren't failing because the application problem for the intrusive stack is written in a confusing manner?