return ends a function, you would only go to the next line if it didnt return

man learning so much from just bashing my head in failure . now is_interger() has entered the chat! thank you for your knowledge

Оставшаяся часть кода после return не будет выполнятся, программа выйдет из функции, поэтому это работает без написания else

its more efficient. however you end up relying on built in functions

It doesn't, but: "You may assume the parameter is non-negative."

return -1 is ours else

How will it work for negative integer values?

Seems like your N's is to small to see benefits from Counter. Your solution is O(n^2), so for large N, your solution will be much slower than op's solution (wich is O(n))

This doesn't work with integers that are too large to fit into a 64-bit float though.
Try find_next_square(2**1024) for instance.