toString with map and sum

object ArmstrongNumbers {
  def isArmstrongNumber(num: Int): Boolean = {
    val text = num.toString()
    val len: Double = text.length()
    text.map(chr => Math.pow(chr.asDigit, len)).sum == num
  }
}

This approach starts be calling the toString() method on the input Int.

After the length is taken of the String, the map() method is called in the String. This passes each character in the String to a lambda which uses asDigit to convert the character to an Int and passes it as the first argument to the pow() method. The second argument is the length of the String.

Since pow() take two Double arguments, the length of the String is set to the Double type to keep from doing a widening conversion of Int to Double on every call to pow().

After map() is done iterating all the characters, the sum() method is called to total all the calls to pow(). The method returns whether that total is equal to the original number.