Solution: Range Operations
This is the expected solution:
fun calculateSumOfSquares(n: Int): Int {
var sum = 0
for (i in 1..n) {
sum += i * i
}
return sum
}
fun calculateSumOfEven(n: Int): Int {
var sum = 0
for (i in 2..n step 2) {
sum += i
}
return sum
}
fun countDownByStep(start: Int, end: Int, step: Int): String {
var result = ""
for (i in start downTo end step step) {
result += i
if (i != end) {
result += ", "
}
}
return result
}
This exercise can also be solved using functions that are presented in the Functional Kotlin book (the next book I recommend you reading after Kotlin Essentials). This is a solution using fold function:
fun calculateSumOfSquares(n: Int): Int =
(1..n).fold(0) { sum, i -> sum + i * i }
fun calculateSumOfEven(n: Int): Int =
(2..n step 2).fold(0) { sum, i -> sum + i }
fun countDownByStep(start: Int, end: Int, step: Int): String =
(start downTo end step step).fold("") { result, i ->
result + i + if (i != end) ", " else ""
}
This is a solution using sumOf, sum and joinToString functions:
fun calculateSumOfSquares(n: Int): Int = (1..n).sumOf { it * it }
fun calculateSumOfEven(n: Int): Int = (0..n step 2).sum()
fun countDownByStep(start: Int, end: Int, step: Int): String =
(start downTo end step step).joinToString(separator = ", ")
Example solution in playground
import org.junit.Test
import kotlin.test.assertEquals
fun calculateSumOfSquares(n: Int): Int {
var sum = 0
for (i in 1..n) {
sum += i * i
}
return sum
}
fun calculateSumOfEven(n: Int): Int {
var sum = 0
for (i in 2..n step 2) {
sum += i
}
return sum
}
fun countDownByStep(start: Int, end: Int, step: Int): String {
var result = ""
for (i in start downTo end step step) {
result += i
if (i != end) {
result += ", "
}
}
return result
}
fun main() {
// Examples for calculateSumOfSquares
println(calculateSumOfSquares(0)) // 0
println(calculateSumOfSquares(1)) // 1
println(calculateSumOfSquares(2)) // 5 (1 + 4)
println(calculateSumOfSquares(3)) // 14 (1 + 4 + 9)
println(calculateSumOfSquares(4)) // 30 (1 + 4 + 9 + 16)
// Example for calculateSumOfEven
println(calculateSumOfEven(0)) // 0
println(calculateSumOfEven(1)) // 0
println(calculateSumOfEven(2)) // 2
println(calculateSumOfEven(3)) // 2
println(calculateSumOfEven(5)) // 6 (2 + 4)
println(calculateSumOfEven(10))
// 30 (2 + 4 + 6 + 8 + 10)
println(calculateSumOfEven(12))
// 42 (2 + 4 + 6 + 8 + 10 + 12)
println(calculateSumOfEven(20))
// 110 (2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20)
// Example for countDownByStep
println(countDownByStep(1, 1, 1)) // 1
println(countDownByStep(5, 1, 2)) // 5, 3, 1
println(countDownByStep(10, 1, 3)) // 10, 7, 4, 1
println(countDownByStep(15, 5, 5)) // 15, 10, 5
println(countDownByStep(20, 2, 3))
// 20, 17, 14, 11, 8, 5, 2
println(countDownByStep(10, 4, 3)) // 10, 7, 4
println(countDownByStep(-1, -1, 1)) // -1
println(countDownByStep(-5, -9, 2)) // -5, -7, -9
}
class LoopsTest {
@Test
fun testCalculateSumOfSquares() {
assertEquals(1, calculateSumOfSquares(1))
assertEquals(5, calculateSumOfSquares(2))
assertEquals(14, calculateSumOfSquares(3))
assertEquals(30, calculateSumOfSquares(4))
assertEquals(385, calculateSumOfSquares(10))
assertEquals(0, calculateSumOfSquares(0))
assertEquals(0, calculateSumOfSquares(-1))
assertEquals(0, calculateSumOfSquares(-1))
assertEquals(0, calculateSumOfSquares(-3))
}
@Test
fun testCalculateSumOfEven() {
assertEquals(0, calculateSumOfEven(0))
assertEquals(0, calculateSumOfEven(1))
assertEquals(2, calculateSumOfEven(2))
assertEquals(2, calculateSumOfEven(3))
assertEquals(6, calculateSumOfEven(5))
assertEquals(30, calculateSumOfEven(10))
assertEquals(42, calculateSumOfEven(12))
assertEquals(110, calculateSumOfEven(20))
assertEquals(240, calculateSumOfEven(30))
assertEquals(0, calculateSumOfEven(-1))
}
@Test
fun testCountDownByStep() {
assertEquals("1", countDownByStep(1, 1, 1))
assertEquals("5, 3, 1", countDownByStep(5, 1, 2))
assertEquals("10, 7, 4, 1", countDownByStep(10, 1, 3))
assertEquals("15, 10, 5", countDownByStep(15, 5, 5))
assertEquals("20, 17, 14, 11, 8, 5, 2", countDownByStep(20, 2, 3))
assertEquals("10, 7, 4", countDownByStep(10, 4, 3))
assertEquals("-1", countDownByStep(-1, -1, 1))
assertEquals("-5, -7, -9", countDownByStep(-5, -9, 2))
assertEquals("0", countDownByStep(0, 0, 1))
assertEquals("0", countDownByStep(0, 0, 2))
}
}
