I'm 4/6 for recursive solutions! And today's a dou...

# advent-of-code

[Edgars]

I'm 4/6 for recursive solutions! And today's a double whammy!
https://github.com/edgars-supe/advent-of-code/blob/master/src/main/kotlin/lv/esupe/aoc/year2019/Day6.kt

[karelpeeters]

We need persistent lists, that pathToCom function just hurts to think about!

[Edgars]

How do you mean?

[karelpeeters]

It's making a copy of the list on every recursion step, so that O(n^2) allocated memory and time just to build a list.

[Edgars]

private tailrec fun MutableList<String>.pathToCom(from: String) {
    val next = input[from] ?: return
    add(next)
    pathToCom(next)
}

Runs in almost half the time... from ~0.9ms to ~0.45ms.

[nils]

I like to use https://github.com/Kotlin/kotlinx.collections.immutable for persistent lists