if he used const that makes him can't erase

It's bad practice to remove them. It's relying on the tests to include them instead, which leaves these solutions prone to being automatically invalidated in the future if the tests change and their solutions don't compile anymore. The line or two saved by omitting them isn't worth that risk, so you're doing good by keeping them in

why theres no #include
i tried it without the lib but dosnt work for me

Very readable and logical. Oh, this language design...

where did 'const' go?

isn't it an efficient way to store the sqrt result in a variable rather than doing it twice?

gg

wow that's actually really clever, I wasn't able to underdstad the logic till you explained, thanks

Simple and clever!
well done!

Mate, this is beautiful. Simple, elegant and easy to understand, even for a beginner like me. Thanks a lot!