in that case in order to passe the tests we shall do to int conversion, will it still be the best practice for this exercice? I used " function summation($n) : int "

Use spoiler flag next time, please.

That's great. But to better protect against overflow with very big $n, i like to write it as "$n/2 * ($n+1)", this way $n will never multiply with $n+1 before the division.

This is the best practice

I'd have liked to use ternary operators on this one, but seemed more complex than usual. Y'know, replacing if and else, considering the 0 values weren't adding up to the final result.

i agree it will re execute the count in each iteration, but maybe he leave it like that to save 1 line of code at the cost of little eficiency.

It doesn't count it, it adds it, and adding 0 is neutral, so...

This solution counts 0 as negative, and 0 is neither positive nor negative.

Why does this work?

I loved this solution!

another note: it is common practice in go to put the if present check all on one line.

  if _, present := m[w]; present {
    return false
  }

you can look at my solution for a full example

This is not the best practice, because it always runs O(n). Even if the first two chars in the string are equal, it would iterate on all other chars.