Exercise: Range Operations

Implement the following functions using range operations:

• calculateSumOfSquares function that takes an integer n as an argument and returns the sum of the squares of all positive integers from 0 to n.
• calculateSumOfEven function that takes an integer n as an argument and returns the sum of all even numbers from 0 to n.
• countDownByStep function that takes three integers: start, end, and step, and returns a string representation of the numbers from start down to end, with each step being step units apart.

fun calculateSumOfSquares(n: Int): Int = TODO()

fun calculateSumOfEven(n: Int): Int = TODO()

fun countDownByStep(
    start: Int,
    end: Int,
    step: Int
): String = TODO()

Example usage:

// 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

This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in essentials/loops/Loops.kt. You can find there starting code, example usage and unit tests.

Once you are done with the exercise, you can check your solution here.

Playground

import org.junit.Test
import kotlin.test.assertEquals

fun calculateSumOfSquares(n: Int): Int = TODO()

fun calculateSumOfEven(n: Int): Int = TODO()

fun countDownByStep(
    start: Int,
    end: Int,
    step: Int
): String = TODO()

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))
    }
}