Memory-efficient data structures in Android

For the following code, enter the missing data structure class name.

data class City(val name: String, val population: Int, val yearOfFoundation: Int)

val cities = ________<City>()
cities.add(City("Toronto", 2731571, 1793))
cities.add(City("Tokyo", 37274000, 1943))
cities.add(City("Ufa", 1135061, 1574))
println(cities.sortedBy { it.yearOfFoundation }.first())