git-random | Chrome extension - Replaces new tab | Browser Plugin library

So the range you define (0..9) is actually already a sequence of numbers. Instead of iterating and repeatedly generating a new random, you can just use a subset of that sequence. In fact, this is the accepted answer's solution to the question you linked. Here are some pointers if you want to implement it yourself to get the practice:

• The first for loop in that solution is unnecessary in Kotlin because of the range. 0..9 does the same thing, you're on the right track there.

• In Kotlin you can call .shuffled() directly on the range without needing to call Collections.shuffle() with an argument like they do.

• You can avoid another loop if you create a string from the whole range and then return a substring.

If you want to look at my solution (with input from others in the comments), it is in a spoiler here:

fun getUniqueNumber(length: Int) = (0..9).shuffled().take(length).joinToString('')

(Note that this doesn't gracefully handle a length above 10, but that's up to you to figure out how to implement. It is up to you to use subList() and then toString(), or toString() and then substring(), the output should be the same.)