Challange

you have one list of numbers like : (1,2,3) with no fixed length ( could contain 1 or 10000 ) itams.

Want to have a funktion that forfills the following requirements:

give you all possible kombinations in one list back
No Duplicates in direct order like (123112) double a number like that is prhibitit.
No Duplicates il lager sections like (12 123 123 12)

an example of an possible Result:

(1,3,1,2,3,2,1) build an algorythem that crate an list as defined wiht as less computional steps as possibe.

How to use that?

you can commit any solutions in any programming language. or a formalisation of the problem or idea.

if you solve it firstly i am going to invite you to a cofee or mate ^^