Why does the function not work without the "if" statement?

Issue

This function returns a list containing all numbers from n to 0.
If I deleted the "if" statement the function doesn't work, even if the parameters aren't 0.
Why is that?

fun countDown (n : Int): List<Int> {
    if (n == 0) {
        return listOf(0)
    }

    return mutableListOf(n).also { it.addAll(countDown(n - 1)) }
}

Solution

Your code calls it.addAll(countDown(n-1)), specifically calling countDown(n-1)

So a direct call to, say, countDown(3) will call countDown(2); countDown(2) calls countDown(1); countDown(1) calls countDown(0).

Answered By - ralphmerridew