sum_digits.rb

# Sum all the digits

#   Write a program that takes a positive number as an input.
#   The program should take every single digit of this number,
#   and sum them until only a 1 digit number is left.

#   Example input: 31337

#   Output: 8 (because 3+1+3+3+7=17 and 1+7=8)

#   Please add a benchmark for your solution.

# Usage
# > SumDigit.run 912931241291293124129129312412

require 'inline'

class SumDigit

  def self.run_with_each_char(number) # 1st
    while number > 9 do
      sum = 0
      number.to_s.each_char { |c| sum += c.to_i }
      number = sum
    end
    number
  end

  def self.run_with_split(number) # 2nd
    while number > 9 do
      sum = 0
      number.to_s.split('').each { |c| sum += c.to_i }
      number = sum
    end
    number
  end

  def self.run_with_mod(number) # 3rd
    while number > 9 do
      sum = 0
      while number > 0 do
        sum += number % 10
        number /= 10
      end

      number = sum
    end
    number
  end

  class << self
    alias :run :run_with_each_char
  end

end

require 'benchmark'

test_number = 912923124541291293130241291290332124453534412745985591342932112041291209312411529720129312412349082109120942834938750395063473621032432480357565234

Benchmark.bm do |x|
  x.report { SumDigit.run_with_each_char test_number }
  x.report { SumDigit.run_with_split test_number }
  x.report { SumDigit.run_with_mod test_number }
end