Having fun with basic structs, and was looking into intersect 2 ordered IntArray together. I know I can do something like

first.intersect(second.toList()).toIntArray()

but this is not really O(n). It takes more time than just using standard comparison one by one (using the property that the 2 IntArrays are ordered). I wonder if there is something elegant to solve this in Kotlin? An ugly way to do this fast would be with something like

private fun intersection(a: IntArray, b: IntArray): IntArray {
        val c = IntArray(min(a.size, b.size))
        if (c.isEmpty()) {
            return c
        }
        var i = 0
        var j = 0
        var k = 0
        while (i < a.size && j < b.size) {
            val aa = a[i]
            val bb = b[j]
            val comparison = aa - bb
            if (comparison == 0) {
                c[k++] = aa
                i++
                j++
            } else if (comparison < 0) {
                i++
            } else {
                j++
            }
        }
        return c.copyOf(k)
    }

fundamentally this is the intersection of two sorted arrays/collections...if that helps you search for anything

it is indesd. I did search yeah, nothing that can help me take advantage of the int position

I think given this kind of thing is performance-sensitive, anything fancier would probably be slower...I guess my main concern is is there any way we can avoid the copy. maybe take

(data: IntArray, size: Int) -> Unit

as a third argument and pass

c, k

directly to that. though admittedly that'd look a little weird.

minor note:

min()

is not in kotlin stdlib,

minOf()

is

compareTo

ftw

I'd probably write something generic like this but if you're sticking with

IntArray

for performance then I'm not sure there's much else you can do

hm. does Array implement Iterable?

that would incur boxing overhead which doesn't exist with IntArray

thanks folks!