Kotlin 벤드펴기 목록 – 문제 및 솔루션

public fun  Iterable>.flatten(): List

data class Customer(
    val name: String,
    val age: Int
)

fun main(args : Array){
    val list = listOf(
            listOf(1, 2, 3),
            listOf("one", "two", "three"),
            listOf(Customer("Jack", 25), Customer("Peter", 31), Customer("Mary", 18))
    )
    
    var flattenList = list.flatten()
    
    println(list)
    /*
        [[1, 2, 3], [one, two, three], [Customer(name=Jack, age=25), Customer(name=Peter, age=31), Customer(name=Mary, age=18)]]
    */
    println(flattenList)
    /*
        [1, 2, 3, one, two, three, Customer(name=Jack, age=25), Customer(name=Peter, age=31), Customer(name=Mary, age=18)]
    */
}