This is the best solution and if you have something to tell shut up please ;)

it inverses the bool.

code representation:

bool b = true;
std::cout << b << '\n'; // true
std::cout << !b << '\n'; // false

it's called the NOT operator.

visual representation:

true ------[!]------> false
false ------[!]------> true

If this was solved on your own and not via GPT Chat, you are a genius.

it is a container like vector i think (Data Structure)

Is string a vector?

simple as that... nice one

where is conversion of Boolean to a String?

Why fightResolve('A', 'a') must return 'a' in test cases? The description says: "If a matchup occurs that was not previously mentioned (for example Archers vs Pikemen) the attacker will always win." So attacker is first argument, 'A' in this case. Or did I miss something?

Of course, as you please. It's just a way of bounding logic together for good readability

() can be omitted

Cool and fast solution!!