no, this solution about a lot of copiyng

too much copiyng

WTF

It's funny because this was actually pretty much my original answer, except that I didn't account for numbers less than zero.
The error message wasn't very helpful, so I found myself jumping through hoops trying to figure out how to handle floating point inaccuracies.

I feel smartn't seeing this

Seemed like a simple task, but I broke my head solving it, 2 out of 3 conditions in the task were met and the last one was not accepted by me. Of course, I had to resort to help....... It turned out to be the same thing I wrote, just with some minor changes, which also turned out to be tricky, but now I see that it's even easier. I'm going to be a wreck today, work in 4 hours and I haven't slept.....

Looks very simple, clear, and easy. Thank you! As for me: as always I created more complicated solution :)

https://en.cppreference.com/w/cpp/numeric/math/sqrt

I have checked the following source: https://cplusplus.com/reference/cmath/sqrt/?kw=sqrt, and it did not say that std :: sqrt returns NaN when the argument is negative.
Could you please point out the source of your information? I will check that source if it is more reliable/updated.

std::map is actually O(logn) to find. A hashmap (std::unordered_map) would be what to use for efficiency

Fantastic. I was trying to create this simple O(n) O(n) solution. Only when you see it do you realise how simple it is. Kicking myself, as I was almost there twice but deleted and went down other avenues.
Great work.

agree.

Why is this answer getting so many best practice votes? Surely since sqrt returns a floating point value, with which arithmatic is limited in precision, which could cause false answers. It would also risk undefined behaviour due to integer overflow with larger n values as squaresquare (square_rootsquare_root) reaches the max value for an int.
Calculating square roots is also much slower than other integer operations so its not really an efficient approach. Am i mistaken here or missing something?

No need to check for negatives sqrt returns -NAN for negatives square it and it gives you NAN.