fun main(args: Array<String>) {
    val a = listOf(3, 5, 2, 3, 6, 1)
    println(quicksort(a))
}

fun <T: Comparable<T>> quicksort(items: List<T>): List<T>{
    if (items.isEmpty()) return emptyList()
    val pivot = items[0]
    val equal = items.filter { it == pivot }
    val less = items.filter { it < pivot }
    val greater = items.filter { it > pivot }
    return quicksort(less) + equal + quicksort(greater)
}