you will change opinion when you will see that in fact, recursion is the only one way to go with for fast.

ho ok, i'm surprise but well... i have to work more on this. Thank you for check my code and provide an answer.

look at my code, i didn't calculate the factorial and solution is a mathematical sum who is very quick... it should not refused due to server time error... also, what does server time error has in relation with an objective test ? I missunderstand the idea, because if the server has a full load, what does it happend ? you trash users who provide an efficient solution ?

same problem there. I get manage the mathematic solution who doesn't need to calcul the factorial and who have only one loop to get a sum requested for the solution. All tests are green, but attempt said server time ran out... i can not imagine what can be different to pass the server time obstruction. On my computer, there is no significative delay as long as it is very simple.
In fact, i got an answer show me that my solution was too slow... i do simplification for remove the sum part, but again... too slow.

You absolutly no need to calcul a factorial for get the trailing zero in the result of a factorial. It is just a mathematic problem where only sum and power and division is required.

it is just wrong... why a wrong answer could be a good practice ?