Exercism: Armstrong Numbers (Ruby)

A presentation outlining my solution to the Exercism Armstrong Numbers problem in Ruby (https://exercism.io/tracks/ruby/exercises/armstrong-numbers).

Presented at the Sydney Ruby on Rails meetup on 10 September 2019.

Presentation slide deck markdown and speaker notes (useable in Deckset 2):
https://github.com/paulfioravanti/presentations/tree/master/exercism_ruby_armstrong_numbers

Transcript

1. Armstrong Numbers
4. Narcissist Number
5. Armstrong Number
6. Sum of its own digits
7. Raised to the power of the number of its digits
8. Armstrong Numbers
9. Armstrong Numbers ✅ 9
10. Armstrong Numbers ✅ 9 = 9^1 = 9
11. Armstrong Numbers ✅ 9 = 9^1 = 9 ❌ 10
12. Armstrong Numbers ✅ 9 = 9^1 = 9 ❌ 10 != 1^2 + 0^2 = 1
13. Armstrong Numbers ✅ 153 = 1^3 + 5^3 + 3^3 = 153
14. Armstrong Numbers ✅ 153 = 1^3 + 5^3 + 3^3 = 153 ❌ 154 != 1^3 + 5^3 + 4^3 = 190
15. Armstrong Numbers
16. Armstrong Numbers ! Get the number of digits
17. Armstrong Numbers ! Get the number of digits ! Calculate the power of each digit
18. Armstrong Numbers ! Get the number of digits ! Calculate the power of each digit ! Sum all the powers
19. ! Take 1
20. Get number of digits
21. Get number of digits module ArmstrongNumbers module_function def include?(number) end end
22. ArmstrongNumbers.include?(154)
23. Get number of digits module ArmstrongNumbers module_function def include?(number) end end
24. Get number of digits module ArmstrongNumbers module_function def include?(number) number end end
25. Get number of digits module ArmstrongNumbers module_function def include?(number) number .digits end end
26. Sum Powers module ArmstrongNumbers module_function def include?(number) number .digits .then(&method(:sum_powers)) end end
27. Sum Powers module ArmstrongNumbers module_function def include?(number) sum = number .digits .then(&method(:sum_powers)) end end
28. Sum Powers module ArmstrongNumbers module_function def include?(number) sum = number .digits .then(&method(:sum_powers)) sum == number end end
29. Sum Powers module ArmstrongNumbers module_function # ... def sum_powers(digits) end private_class_method :sum_powers end
30. Sum Powers module ArmstrongNumbers module_function # ... def sum_powers(digits) digits end private_class_method :sum_powers end
31. Sum Powers module ArmstrongNumbers module_function # ... def sum_powers(digits) digits .each end private_class_method :sum_powers end
32. Sum Powers module ArmstrongNumbers module_function # ... def sum_powers(digits) digits .each .with_object(digits.length) end private_class_method :sum_powers end
33. Sum Powers module ArmstrongNumbers module_function # ... def sum_powers(digits) digits .each .with_object(digits.length) .sum(&method(:power)) end private_class_method :sum_powers end
34. Calculate Power of Each Digit module ArmstrongNumbers module_function # ... def power((digit, length)) digit**length end private_class_method :power end
35. 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
38. exercism submit armstrong_numbers.rb
39. Done!
40. Done?
41. Complex...?
42. ! Take 2
43. module ArmstrongNumbers module_function def include?(number) end end
44. module ArmstrongNumbers module_function def include?(number) digits = number.digits end end
45. module ArmstrongNumbers module_function def include?(number) digits = number.digits length = digits.length end end
46. module ArmstrongNumbers module_function def include?(number) digits = number.digits length = digits.length number == digits.sum { |digit| digit**length } end end
48. Choose Your Own Adventure
49. You'll rarely get it right the first *me
50. Submit o)en, get feedback
51. Read other people's code
52. Refactor un,l you're happy
53. github.com/paulfioravanti/exercism
54. BONUS FACTOIDS!
55. BONUS FACTOIDS! ! Number of Armstrong numbers is finite
56. BONUS FACTOIDS! ! Number of Armstrong numbers is finite ! Only 88 Armstrong numbers in Base 10
57. 115,132,219,018, 763,992,565,095, 597,973,971,522,401
59. Thanks! @paulfioravanti