Solution: Optimize collection processing
fun List<StudentJson>.getPassingSurnames(): List<String> = this
.filter { it.result >= 50 && it.pointsInSemester >= 15 }
.mapNotNull { it.surname }
I needed to break the function definition to fit the page. In actual code, I would not do that.
Example solution in playground
import junit.framework.TestCase.assertEquals
import org.junit.Test
data class StudentJson(
val name: String?,
val surname: String?,
val result: Double,
val pointsInSemester: Int
)
fun List<StudentJson>.getPassingSurnames(): List<String> = this
.filter { it.result >= 50 && it.pointsInSemester >= 15 }
.mapNotNull { it.surname }
class PassingSurnamesTest {
@Test
fun `should return passing surnames`() {
val students = listOf(
StudentJson("John", "Smith", 60.0, 20),
StudentJson("Jane", "Doe", 45.0, 20),
StudentJson("Ivan", "Ivanov", 60.0, 10),
StudentJson("John", "Doe", 30.0, 10),
StudentJson("Jake", "Simonson", 80.0, 20),
)
assertEquals(
listOf("Smith", "Simonson"),
students.getPassingSurnames()
)
}
}
