Shop.kt

data class Shop(val name: String, val customers: List<Customer>)

data class Customer(val name: String, val city: City, val orders: List<Order>)

data class Order(val products: List<Product>, val isDelivered: Boolean)

data class Product(val name: String, val price: Double)

data class City(val name: String)

fun getCityThatMostCustomersAreFrom(): City? {
    TODO()
}

fun getCustomerWithMaximumNumberOfOrders(): Customer? {
    TODO()
}