Solution: Refactor collection processing
fun List<StudentGrades>.getBestForScholarship(
semester: String
): List<StudentGrades> = this
.filter { s ->
s.grades
.filter { it.semester == semester && it.passing }
.sumOf { it.ects } > 30
}
.sortedByDescending {
averageGradeFromSemester(it, semester)
}
.take(10)
fun averageGradeFromSemester(
student: StudentGrades,
semester: String
): Double = student.grades
.filter { it.semester == semester }
.map { it.grade }
.average()
Example solution in playground
import org.junit.Test
import java.util.Collections
import kotlin.random.Random
import kotlin.test.assertEquals
fun List<StudentGrades>.getBestForScholarship(
semester: String
): List<StudentGrades> = this
.filter { s ->
s.grades
.filter { it.semester == semester && it.passing }
.sumOf { it.ects } > 30
}
.sortedByDescending {
averageGradeFromSemester(it, semester)
}
.take(10)
fun averageGradeFromSemester(
student: StudentGrades,
semester: String
): Double = student.grades
.filter { it.semester == semester }
.map { it.grade }
.average()
data class Grade(
val passing: Boolean,
var ects: Int,
var semester: String,
var grade: Double
)
data class StudentGrades(
val studentId: String,
val grades: List<Grade>
)
class StudentGradesIntenshipTest {
@Test
fun `should return best students for scholarship`() {
val r = Random(123456789)
val grades = List(100) {
StudentGrades(
"S$it",
List(100) {
Grade(
passing = r.nextBoolean(),
ects = r.nextInt(5) + 1,
semester = "Semester ${r.nextInt(5)}",
grade = r.nextDouble() * 5 + 2.0
)
}
)
}
val res1 = grades.getBestForScholarship("Semester 0")
assertEquals(
listOf("S83", "S47", "S26", "S53", "S4", "S29", "S50", "S34", "S44", "S59"),
res1.map { it.studentId },
)
assertEquals(
listOf("S30", "S66", "S49", "S14", "S6", "S12", "S25", "S99", "S7", "S40"),
grades.getBestForScholarship("Semester 1").map { it.studentId }
)
}
@Test
fun `should return empty list if no students passed`() {
val grades = listOf(
StudentGrades(
"S1",
listOf(
Grade(false, 5, "Semester 0", 3.0),
Grade(false, 5, "Semester 1", 3.0),
Grade(false, 5, "Semester 2", 3.0),
Grade(false, 5, "Semester 3", 3.0),
Grade(false, 5, "Semester 4", 3.0),
)
),
StudentGrades(
"S2",
listOf(
Grade(false, 5, "Semester 0", 3.0),
Grade(false, 5, "Semester 1", 3.0),
Grade(false, 5, "Semester 2", 3.0),
Grade(false, 5, "Semester 3", 3.0),
Grade(false, 5, "Semester 4", 3.0),
)
),
StudentGrades(
"S3",
listOf(
Grade(false, 5, "Semester 0", 3.0),
Grade(false, 5, "Semester 1", 3.0),
Grade(false, 5, "Semester 2", 3.0),
Grade(false, 5, "Semester 3", 3.0),
Grade(false, 5, "Semester 4", 3.0),
)
),
)
assertEquals(
emptyList<String>(),
grades.getBestForScholarship("Semester 0").map { it.studentId }
)
}
@Test
fun `should sort by average grade for semester`() {
val grades = listOf(
StudentGrades(
"S1",
listOf(
Grade(true, 25, "Semester 1", 3.0),
Grade(true, 25, "Semester 1", 3.0),
)
),
StudentGrades(
"S2",
listOf(
Grade(true, 50, "Semester 1", 4.0),
Grade(true, 50, "Semester 2", 1.0),
Grade(true, 50, "Semester 3", 1.0),
Grade(true, 50, "Semester 4", 1.0),
)
),
StudentGrades("S3", listOf(Grade(true, 50, "Semester 1", 5.0),)),
)
assertEquals(
listOf("S3", "S2", "S1"),
grades.getBestForScholarship("Semester 1").map { it.studentId }
)
}
@Test
fun `should return 10 best students`() {
val grades = List(100) {
StudentGrades(
"S$it",
listOf(
Grade(
passing = true,
ects = 50,
semester = "Semester 0",
grade = 5.0 + (0.01 * it)
)
)
)
}
assertEquals(
List(10) { "S${99 - it}" },
grades.getBestForScholarship("Semester 0").map { it.studentId }
)
}
@Test
fun `should calculate average grade from semester`() {
assertEquals(
3.0,
averageGradeFromSemester(StudentGrades(
"S1",
listOf(
Grade(true, 25, "Semester 1", 3.0),
Grade(true, 25, "Semester 1", 3.0),
)
), "Semester 1")
)
assertEquals(
3.0,
averageGradeFromSemester(StudentGrades(
"S1",
listOf(
Grade(true, 10, "Semester 1", 2.0),
Grade(true, 20, "Semester 1", 4.0),
)
), "Semester 1")
)
assertEquals(
2.0,
averageGradeFromSemester(StudentGrades(
"S1",
listOf(
Grade(true, 10, "Semester 1", 2.0),
Grade(true, 20, "Semester 2", 4.0),
)
), "Semester 1")
)
}
}
