multiples.rb

require 'benchmark'

def multiples(end_of_range)
  multiple_sum = 0
  multiples_of_three = 0
  while multiples_of_three < end_of_range
    multiple_sum += multiples_of_three
    multiples_of_three += 3
  end

  multiples_of_five = 0
  while multiples_of_five < end_of_range
    unless multiples_of_five % 3 == 0
      multiple_sum += multiples_of_five
    end
    multiples_of_five += 5
  end

  return multiple_sum
end

puts Benchmark.measure { multiples(1000) }
puts multiples(1000)

def sum_mult num
  (1..num-1).to_a.keep_if{|n| n % 3 == 0 || n % 5 == 0}.reduce(:+)
end

puts Benchmark.measure { sum_mult(1000) }
puts sum_mult(1000)


def multiples_inject
  multiples = []
  (1..999).each do |num|
    if num % 3 == 0 || num % 5 == 0
      multiples << num
    end
  end
  multiples.inject(:+)
end

puts Benchmark.measure { multiples_inject }
puts multiples_inject

#   0.000000   0.000000   0.000000 (  0.000033)
# 233168
#   0.000000   0.000000   0.000000 (  0.000222)
# 233168
#   0.000000   0.000000   0.000000 (  0.000174)
# 233168