# | Kotlin Koans |
---|---|
Kotlin Koans - Introduction | |
Kotlin Koans - Conventions | |
Kotlin Koans - Collections | |
Kotlin Koans - Properties | |
Kotlin Koans - Builders | |
Kotlin Koans - Generics |
1 Introduction
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
2 Filter map
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
3 All Any and other predicates
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
4 FlatMap
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
5 Max min
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
// Return a customer whose order count is the highest among all customers
fun Shop.getCustomerWithMaximumNumberOfOrders(): Customer? = customers.maxBy { it.orders.size }
// Return the most expensive product which has been ordered
fun Customer.getMostExpensiveOrderedProduct(): Product? = orders.flatMap { it.products }.maxBy { it.price }
6 Sort
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
// Return a list of customers, sorted by the ascending number of orders they made
fun Shop.getCustomersSortedByNumberOfOrders(): List<Customer> = customers.sortedBy { it.orders.size }
7 Sum
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
// Return the sum of prices of all products that a customer has ordered.
// Note: the customer may order the same product for several times.
fun Customer.getTotalOrderPrice(): Double = orders.flatMap { it.products }.sumByDouble { it.price }
8 GroupBy
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
// Return a map of the customers living in each city
fun Shop.groupCustomersByCity(): Map<City, List<Customer>> = customers.groupBy { it.city }
9 Partition
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
// Return customers who have more undelivered orders than delivered
fun Shop.getCustomersWithMoreUndeliveredOrdersThanDelivered(): Set<Customer> = customers.filter {
val (delivered, undelivered) = it.orders.partition { it.isDelivered }
undelivered.size > delivered.size
}.toSet()
10 Fold
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
// Return the set of products that were ordered by every customer
fun Shop.getSetOfProductsOrderedByEveryCustomer(): Set<Product> {
val allProducts = customers.flatMap { it.orders.flatMap { it.products }}.toSet()
return customers.fold(allProducts, {
orderedByAll, customer ->
orderedByAll.intersect(customer.orders.flatMap { it.products }.toSet())
})
}
11 Compound tasks
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
// Return the most expensive product among all delivered products
// (use the Order.isDelivered flag)
fun Customer.getMostExpensiveDeliveredProduct(): Product? {
return orders.filter { it.isDelivered }.flatMap { it.products }.maxBy { it.price }
}
// Return how many times the given product was ordered.
// Note: a customer may order the same product for several times.
fun Shop.getNumberOfTimesProductWasOrdered(product: Product): Int {
return customers.flatMap { it.getOrderedProductsList() }.count { it == product }
}
fun Customer.getOrderedProductsList(): List<Product> {
return orders.flatMap { it.products }
}
12 Get used to new style
#TestShop.kt & Shop.kt 문서를 참고하십시오.
Kotlin
Copy
fun doSomethingStrangeWithCollection(collection: Collection<String>): Collection<String>? {
val groupsByLength = collection. groupBy { s -> s.length }
val maximumSizeOfGroup = groupsByLength.values.map { group -> group.size }.max()
return groupsByLength.values.firstOrNull { group -> group.size == maximumSizeOfGroup }
}
13 TestShop.kt & Shop.kt
TestShop.kt
Kotlin
Copy
//products
val idea = Product("IntelliJ IDEA Ultimate", 199.0)
val reSharper = Product("ReSharper", 149.0)
val dotTrace = Product("DotTrace", 159.0)
val dotMemory = Product("DotTrace", 129.0)
val dotCover = Product("DotCover", 99.0)
val appCode = Product("AppCode", 99.0)
val phpStorm = Product("PhpStorm", 99.0)
val pyCharm = Product("PyCharm", 99.0)
val rubyMine = Product("RubyMine", 99.0)
val webStorm = Product("WebStorm", 49.0)
val teamCity = Product("TeamCity", 299.0)
val youTrack = Product("YouTrack", 500.0)
//customers
val lucas = "Lucas"
val cooper = "Cooper"
val nathan = "Nathan"
val reka = "Reka"
val bajram = "Bajram"
val asuka = "Asuka"
val riku = "Riku"
//cities
val Canberra = City("Canberra")
val Vancouver = City("Vancouver")
val Budapest = City("Budapest")
val Ankara = City("Ankara")
val Tokyo = City("Tokyo")
fun customer(name: String, city: City, vararg orders: Order) = Customer(name, city, orders.toList())
fun order(vararg products: Product, isDelivered: Boolean = true) = Order(products.toList(), isDelivered)
fun shop(name: String, vararg customers: Customer) = Shop(name, customers.toList())
val shop = shop("jb test shop",
customer(lucas, Canberra,
order(reSharper),
order(reSharper, dotMemory, dotTrace)
),
customer(cooper, Canberra),
customer(nathan, Vancouver,
order(rubyMine, webStorm)
),
customer(reka, Budapest,
order(idea, isDelivered = false),
order(idea, isDelivered = false),
order(idea)
),
customer(bajram, Ankara,
order(reSharper)
),
customer(asuka, Tokyo,
order(idea)
),
customer(riku, Tokyo,
order(phpStorm, phpStorm),
order(phpStorm)
)
)
val customers: Map<String, Customer> = shop.customers.fold(hashMapOf<String, Customer>(), {
map, customer ->
map[customer.name] = customer
map
})
val orderedProducts = setOf(idea, reSharper, dotTrace, dotMemory, rubyMine, webStorm, phpStorm)
val sortedCustomers = listOf(cooper, nathan, bajram, asuka, lucas, riku, reka).map { customers[it] }
val groupedByCities = mapOf(
Canberra to listOf(lucas, cooper),
Vancouver to listOf(nathan),
Budapest to listOf(reka),
Ankara to listOf(bajram),
Tokyo to listOf(asuka, riku)
).mapValues { it.value.map { name -> customers[name] } }
Shop.kt
Kotlin
Copy
data class Shop(val name: String, val customers: List<Customer>)
data class Customer(val name: String, val city: City, val orders: List<Order>) {
override fun toString() = "$name from ${city.name}"
}
data class Order(val products: List<Product>, val isDelivered: Boolean)
data class Product(val name: String, val price: Double) {
override fun toString() = "'$name' for $price"
}
data class City(val name: String) {
override fun toString() = name
}
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