What is an efficient way to add an item at regular interval - list

Question

I have dogs list and I need to Add Cat object in 2nd position in between every 6 dogs. What is the efficient way to do this?
fun main(args: Array<String>) {
insertCatBetweenDogs()
}
fun insertCatBetweenDogs() {
val dogs = mutableListOf<String>()
for (i in 1..14) {
dogs.add("Dog$i")
}
val chunkedDogs = dogs.chunked(6)
val dogsWithcat = mutableListOf<String>()
chunkedDogs.map { sixDogs ->
sixDogs.mapIndexed { index, chunkedDog ->
if (index!= 0 && index / 2 == 0) {
dogsWithcat.add("Cat")
}
dogsWithcat.add(chunkedDog)
}
}
dogsWithcat.mapIndexed { i, it ->
println(it)
if ((i+1) % 7 == 0) {
println("______________")
println("")
}
}
}
OutPut:
Dog1 Cat Dog2 Dog3 Dog4 Dog5 Dog6
______________
Dog7 Cat Dog8 Dog9 Dog10 Dog11 Dog12
______________
Dog13 Cat Dog14

Answer 1

This will do it
interface Animal
data class Dog(val name: String) : Animal
data class Cat(val name: String) : Animal
val dogs: List<Animal> = List(20) { Dog(it.toString()) }
val cats: List<Animal> = List(4) { Cat(it.toString()) }
val result = dogs
.chunked(6)
.mapIndexed { index, dogs -> dogs.toMutableList().apply { add(1, cats[index]) } }
.flatten()
This prints
[Dog(name=0), Cat(name=0), Dog(name=1), Dog(name=2), Dog(name=3), Dog(name=4), Dog(name=5), Dog(name=6), Cat(name=1), Dog(name=7), Dog(name=8), Dog(name=9), Dog(name=10), Dog(name=11), Dog(name=12), Cat(name=2), Dog(name=13), Dog(name=14), Dog(name=15), Dog(name=16), Dog(name=17), Dog(name=18), Cat(name=3), Dog(name=19)]