Solution: Top articles
class TopArticlesGenerator(
private val articles: List<ArticleStatistics>,
) {
fun topArticles(n: Int): List<ArticleStatistics> = articles
.withIndex()
.sortedByDescending { it.value.views }
.take(n)
.sortedBy { it.index }
.map { it.value }
}
Example solution in playground
import junit.framework.TestCase.assertEquals
import org.junit.Test
class TopArticlesGenerator(
private val articles: List<ArticleStatistics>,
) {
fun topArticles(n: Int): List<ArticleStatistics> = articles
.withIndex()
.sortedByDescending { it.value.views }
.take(n)
.sortedBy { it.index }
.map { it.value }
}
data class ArticleStatistics(
val title: String,
val views: Long,
)
fun main() {
val generator = TopArticlesGenerator(
listOf(
ArticleStatistics("Article 1", 400),
ArticleStatistics("Article 2", 100),
ArticleStatistics("Article 3", 200),
ArticleStatistics("Article 4", 300),
ArticleStatistics("Article 5", 500),
ArticleStatistics("Article 6", 0),
)
)
val topArticles = generator.topArticles(3)
topArticles.onEach { println(it) }
// ArticleStatistics(title=Article 1, views=400)
// ArticleStatistics(title=Article 4, views=300)
// ArticleStatistics(title=Article 5, views=500)
}
class TopArticlesTest {
@Test
fun `Top articles are returned in the correct order`() {
val articles = listOf(
ArticleStatistics("Article 1", 400),
ArticleStatistics("Article 2", 100),
ArticleStatistics("Article 3", 200),
ArticleStatistics("Article 4", 300),
ArticleStatistics("Article 5", 500),
ArticleStatistics("Article 6", 0),
)
val generator = TopArticlesGenerator(articles)
val topArticles = generator.topArticles(100)
assertEquals(articles, topArticles)
}
@Test
fun `Only n top articles are kept`() {
val articles = listOf(
ArticleStatistics("Article 1", 400),
ArticleStatistics("Article 2", 100),
ArticleStatistics("Article 3", 200),
ArticleStatistics("Article 4", 300),
ArticleStatistics("Article 5", 500),
ArticleStatistics("Article 6", 0),
)
val generator = TopArticlesGenerator(articles)
val topArticles = generator.topArticles(3)
assertEquals(articles.slice(listOf(0, 3, 4)), topArticles)
}
}
