Kotlin - built-in higher-order functions - Power Up Your Code - filter, forEach

Head First Kotlin
A Brain-Friendly Guide
楽天ブックス(Kobo) 紀伊國屋書店(Kinoppy)

開発環境

• macOS Mojave - Apple (OS)
• Windows 10 Pro (OS)
• IntelliJ IDEA CE(Community Edition) (IDE(統合開発環境))
• Kotlin (プログラミング言語)

Head First Kotlin: A Brain-Friendly Guide (Dawn Griffiths(著)、David Griffiths(著)、O'Reilly Media)のChapter 12(built-in higher-order functions - Power Up Your Code)、Pool Puzzle(379)の解答を求めてみる。

コード

abstract class Pet(var name: String)
class Cat(name: String) : Pet(name)
class Dog(name: String) : Pet(name)
class Fish(name: String) : Pet(name)
class Contest<T : Pet>() {
    var scores: MutableMap<T, Int> = mutableMapOf()
    fun addScore(t: T, score: Int = 0) {
        if (score >= 0) scores.put(t, score)
    }

    fun getWinners(): Set<T> {
        val highScore = scores.values.max()
        val winners = scores.filter { it.value == highScore }.keys
        winners.forEach { println("Winner: ${it.name}") }
        return winners
    }
}

fun main() {
    val cat1 = Cat("Cat1")
    val cat2 = Cat("Cat2")
    val dog1 = Dog("Dog1")
    val dog2 = Dog("Dog2")
    val fish1 = Fish("Fish1")
    val fish2 = Fish("Fish2")
    val contest = Contest<Pet>()

    for (n in 1..5) {
        println("第${n}回")
        listOf(cat1, cat2, dog1, dog2, fish1, fish2)
            .forEach({ contest.addScore(it, kotlin.random.Random.nextInt(5)) })

        val winners = contest.getWinners()

        contest.scores.forEach { println("${it.key.name} ${it.value}") }
    }
}

入出力結果

第1回
Winner: Cat2
Winner: Fish1
Cat1 3
Cat2 4
Dog1 2
Dog2 2
Fish1 4
Fish2 2
第2回
Winner: Cat1
Winner: Cat2
Winner: Dog2
Winner: Fish1
Cat1 4
Cat2 4
Dog1 2
Dog2 4
Fish1 4
Fish2 0
第3回
Winner: Cat2
Winner: Fish1
Winner: Fish2
Cat1 2
Cat2 4
Dog1 3
Dog2 1
Fish1 4
Fish2 4
第4回
Winner: Cat2
Winner: Fish1
Cat1 2
Cat2 4
Dog1 2
Dog2 3
Fish1 4
Fish2 3
第5回
Winner: Fish2
Cat1 1
Cat2 1
Dog1 1
Dog2 0
Fish1 1
Fish2 3

Process finished with exit code 0