i find kotlin’s extensions?

What do you mean? Extension function is just a language feature: https://kotlinlang.org/docs/reference/extensions.html Standard library contains a lot of them, just check reference. For example this is doc for package

kotlin.collections

which contains a lot of extensions for different types, including `Array.reverse()`: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/index.html

also instead of

printArray

or

printStringArray

you can just use array extension

*Array.contentToString()

I think trying to reimplement all those function is not very efficient way, because instead using very practical and useful standard library to solve some tasks (even tasks just for education or samples) you spending time on implementing what already is part of the language (which also mean that you are not learning stdlib which especially important when you work on some real task in future)

@Roberto Messina Anyway, I also checked your

reverseArray

implementation and it’s expected that it’s not working, you use

for

loop in a wrong way. Not clearly sure what you try to achieve, you probably need range, because your code just iterate array with index and

var nMiddle

just not used (because one in for loop doesn’t override it). And use

withIndex

is not very efficcient way to work with arrays, it creates a lot of overhead (one additional object on every item) for case which can be easily solved without it But maybe you just need range, or something like this:

for (i in (0..nMiddle))