I needed it, so I made it. It takes two sets of lines and merges them alternatingly.

OneOneMerge.kt

import java.util.*

fun main() {
    val scanner = Scanner(System.`in`)
    var last = ""
    val lines1 = mutableListOf<String>()
    do {
        last = scanner.nextLine()
        lines1.add(last)
    } while (last != "$")
    println("Size: ${lines1.size}")
    val lines2 = mutableListOf<String>()
    do {
        last = scanner.nextLine()
        lines2.add(last)
    } while (last != "$")
    println(lines1.mapIndexed { i, s -> "$s\n${if(lines2.size <= i) "" else lines2[i]}" }.filterNot { "$" in it }.joinToString("\n"))

}