Your solution is not O(n), it is somewhere around O(n^2) worst and O(nlogn) best case (with a huge constant factor).

where are more examples?

Hmm... i have O(len(a)) but cant complite last test with big array...

Can someone show me the direction?

Very interesting. There are (at least) 3 ways to solve it and one of them can be implemented by two similar ideas.

Print the input of the tests your code fails, try your code here: https://pythontutor.com/visualize.html#mode=edit

Direct my attention to a problem in my code, please.

Yeah but some careless ppl like me will not notice that until try to solve it and get error. xd
Thanks anyway.

The function's name should be declareWinner not declare_winner.

Sorry... but in C++ the kata has to be redesigned, as is it is a sound example of BAD C translation to C++
I don't raise an issue but...

Codewars is a learning platform

a) use std::unique_ptr if you want to use pointers..
b) but could be better to use refs (Fighter &fighter1) in the call to 'declare_winner' . This would allow to use exactely the kind of prototype stated in the details:

declare_winner(Fighter("Lew", 10, 2), Fighter("Harry", 5, 4), "Lew")

instead of using naked pointers..
c) all pseudo "hidden" parms of Fighter class have setters and getters which is (generally) a bad practice in C++.
d) setHealth() ? should be transformed in "receiveDamage()" returning bool (true) if the fighter is still alive.

sorry if this question is dumb but ive been trying to search for what the 'this.variable' in the object does/ means. in this case its this.name, this.health ect.. but im having a hard time finding an answer i understand well. can anyone explain it at all?