zig_zag.kt

fun main() {
    var delta = -1
    val m = 3
    
    val offsets: List<Int> = (0..10).scan(0) { acc, _ ->
        (acc + delta).also {
            if (it == -m || it == m) {
                delta = -delta
            }
        }
    }
    
    offsets.forEach {v ->
        println((-m..m).map { if (v == it) "*" else " " }.joinToString("_"))
    }
    
}