Student not understanding explanation the 1st, 2nd... and 8th time
Maybe you are stressing things of minor importance. You gave us two examples.
vector&lt;int&gt; copy;
for (int i = 0; i &lt; my_vec.size(); i++)
    copy.push_back(my_vec[i]);

sure is lengthy, and probably also a bit slower than the C++ expert version of
vector&lt;int&gt; copy = my_vec;

But it does its job and is readable (while e.g. to me as a Java guy, I'd struggle to remember that the assignment operator here does a copy of the data structure). And, regarding performance, we all know that in at least 90% of all cases, it doesn't matter. And if it matters, I'd search for a solution where the vector doesn't have to be copied at all.
Regarding Hill Climbing: During 40 years of software development, I rarely ever needed hill climbing, and I've been working in algorithm-sensitive areas. So, unless your students' jobs need things like hill climbing regularly, think of exercises better matching their everyday needs.
To summarize it: You're not preparing that guy for a PhD in computer science (which most probably isn't needed for his job and out of scope for him as well), but giving him some tools to improve the software engineering aspects of his work.
With this guy, I'd switch from a fixed curriculum to practical reviews of production code, concentrating on readability, robustness and structure, looking at code written by different developers. If he struggles there as well, then have a nice, deep talk with him.
EDIT, as requested by OP
Regarding the &quot;nice, deep talk&quot;: If that guy really struggles hard with basic concepts of software engineering, then he'll probably never catch up with the others. That mindset of specifically-structured thinking is not given to everybody. So, he should understand that his talents might be somewhere else.
He can choose whether he wants to pursue his career as a software engineer, with the risk of always staying behind all the others. Or he can find a different role in the team where his talents shine. It might be he is good at understanding the customers' way of thinking, or at hardware development and interfacing, or UI design, or management, or quality assurance, or whatever. Software development teams need so many roles besides coding, there might well be tasks where he can shine.
That's what I'd talk about with him. You should try to make this a positive experience for him. Maybe you already observed some of his talents, so you can suggest some migration path. For that talk, interpersonal skills are most important.