measure the time to get the sum of digits

sum_of_digits.rb

require "benchmark"

# Sum of digits

TARGET = 123456789

def sum_by_s
  TARGET.to_s.chars.map(&:to_i).sum
end

def sum_by_d
  n = TARGET
  sum = 0
  Math.log10(TARGET).ceil.times do
    sum += n % 10
    n /= 10
  end
  sum
end

def sum_by_l
  n = TARGET
  sum = 0
  while n > 0
    sum += n % 10
    n /= 10
  end
  sum
end


n = 100000
Benchmark.bm do |x|
  x.report { n.times{ sum_by_s } }
  x.report { n.times{ sum_by_d } }
  x.report { n.times{ sum_by_l } }
end
# =>
#     user     system      total        real
# 0.210000   0.000000   0.210000 (  0.218448)
# 0.090000   0.000000   0.090000 (  0.090375)
# 0.050000   0.000000   0.050000 (  0.050930)