Kotlin Koans 30 Compound tasks

Compound tasks (Playground)

Description

Implement Customer.getMostExpensiveDeliveredProduct() and Shop.getNumberOfTimesProductWasOrdered() using functions from the Kotlin standard library.

Kotlin標準ライブラリの関数を使用して、Customer.getMostExpensiveDeliveredProduct() および Shop.getNumberOfTimesProductWasOrdered() を実装してください。

Code

// 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 }
}

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