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Published at Aug 16 2019
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Instructions

Test suite

Solution

An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.

For example:

- 9 is an Armstrong number, because
`9 = 9^1 = 9`

- 10 is
*not*an Armstrong number, because`10 != 1^2 + 0^2 = 1`

- 153 is an Armstrong number, because:
`153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153`

- 154 is
*not*an Armstrong number, because:`154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`

Write some code to determine whether a number is an Armstrong number.

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command `sbt test`

in the exercise directory.

For more detailed info about the Scala track see the help page.

Wikipedia https://en.wikipedia.org/wiki/Narcissistic_number

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

```
import org.scalatest.{Matchers, FunSuite}
/** @version 1.0.0 */
class ArmstrongNumbersTest extends FunSuite with Matchers {
test("Single digit numbers are Armstrong numbers") {
ArmstrongNumbers.isArmstrongNumber(5) should be (true)
}
test("There are no 2 digit Armstrong numbers") {
pending
ArmstrongNumbers.isArmstrongNumber(10) should be (false)
}
test("Three digit number that is an Armstrong number") {
pending
ArmstrongNumbers.isArmstrongNumber(153) should be (true)
}
test("Three digit number that is not an Armstrong number") {
pending
ArmstrongNumbers.isArmstrongNumber(100) should be (false)
}
test("Four digit number that is an Armstrong number") {
pending
ArmstrongNumbers.isArmstrongNumber(9474) should be (true)
}
test("Four digit number that is not an Armstrong number") {
pending
ArmstrongNumbers.isArmstrongNumber(9475) should be (false)
}
test("Seven digit number that is an Armstrong number") {
pending
ArmstrongNumbers.isArmstrongNumber(9926315) should be (true)
}
test("Seven digit number that is not an Armstrong number") {
pending
ArmstrongNumbers.isArmstrongNumber(9926314) should be (false)
}
}
```

```
object ArmstrongNumbers {
// https://exercism.io/profiles/gerdreiss
def isArmstrongNumber(number: Int): Boolean = {
val digits = number.toString
val digitize: Char => Int = _.asDigit
val power: Int => Double = math.pow(_, digits.length)
number == digits.map(digitize andThen power).sum
}
// // https://exercism.io/profiles/djmoorejr
// def isArmstrongNumber( i: Int ): Boolean = {
// val len = i.toString.length
// i.toString.map(c => Math.pow(c.asDigit, len).toInt).sum == i
// }
/*
def isArmstrongNumber(param: Int): Boolean = {
def size(int: Int): Int =
if (int <= 0) 0
else 1 + size(int / 10)
val power = size(param)
def calculateSum(f: (Int, Int) => Int)(param: Int): Int =
if (param > 0) f(param % 10, power) + calculateSum(f)(param / 10)
else 0
def calculatePower(base: Int, power: Int): Int =
if (power > 0) base * calculatePower(base, power - 1)
else 1
param == calculateSum(calculatePower)(param)
}
*/
}
```

A huge amount can be learned from reading other peopleâ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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