An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.
9 = 9^1 = 9
10 != 1^2 + 0^2 = 1
153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153
154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190
Write some code to determine whether a number is an Armstrong number.
For installation and learning resources, refer to the Ruby resources page.
For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:
gem install minitest
If you would like color output, you can
require 'minitest/pride' in
the test file, or note the alternative instruction, below, for running
the test file.
Run the tests from the exercise directory using the following command:
To include color from the command line:
ruby -r minitest/pride armstrong_numbers_test.rb
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
require 'minitest/autorun' require_relative 'armstrong_numbers' # Common test data version: 1.1.0 b3c2522 class ArmstrongNumbersTest < Minitest::Test def test_zero_is_an_armstrong_number # skip assert ArmstrongNumbers.include?(0) end def test_single_digit_numbers_are_armstrong_numbers skip assert ArmstrongNumbers.include?(5) end def test_there_are_no_2_digit_armstrong_numbers skip refute ArmstrongNumbers.include?(10) end def test_three_digit_number_that_is_an_armstrong_number skip assert ArmstrongNumbers.include?(153) end def test_three_digit_number_that_is_not_an_armstrong_number skip refute ArmstrongNumbers.include?(100) end def test_four_digit_number_that_is_an_armstrong_number skip assert ArmstrongNumbers.include?(9_474) end def test_four_digit_number_that_is_not_an_armstrong_number skip refute ArmstrongNumbers.include?(9_475) end def test_seven_digit_number_that_is_an_armstrong_number skip assert ArmstrongNumbers.include?(9_926_315) end def test_seven_digit_number_that_is_not_an_armstrong_number skip refute ArmstrongNumbers.include?(9_926_314) end end
module ArmstrongNumbers module_function def include?(number) sum = number .digits .then(&method(:sum_powers)) sum == number end def sum_powers(digits) digits .each .with_object(digits.length) .sum(&method(:power)) end private_class_method :sum_powers def power((digit, length)) digit**length end private_class_method :power end
A huge amount can be learned from reading other people’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.