gistfile1.rb

require 'benchmark'

def loopy_fib(num)
  return 1 if num == 1
  return 1 if num == 2

  x = 1
  y = 1
  a = 0

  (num - 2).times do
    a = x + y
    x = y
    y = a
  end

  a
end

def recursive_fib(n)
  return 1 if n == 1 || n == 2
  recursive_fib(n - 2) + recursive_fib(n - 1)
end

def benchmark(iterations)
  benchmark = Benchmark.measure do
    1.upto(iterations) do |i|
      yield(i)
    end
  end

  benchmark.real
end

1.upto(6) do |i|
  num = i * 5

  puts "computing fib(1) to fib(#{num})"
  puts "  loopy:     %6.5f seconds" % benchmark(num) { |j| loopy_fib(j) }
  puts "  recursive: %6.5f seconds" % benchmark(num) { |j| recursive_fib(j) }
end

#
# Output from my MacBook Pro:
#
# computing fib(1) to fib(5)
#   loopy:     0.00002 seconds
#   recursive: 0.00004 seconds
# computing fib(1) to fib(10)
#   loopy:     0.00003 seconds
#   recursive: 0.00021 seconds
# computing fib(1) to fib(15)
#   loopy:     0.00006 seconds
#   recursive: 0.00226 seconds
# computing fib(1) to fib(20)
#   loopy:     0.00019 seconds
#   recursive: 0.02350 seconds
# computing fib(1) to fib(25)
#   loopy:     0.00022 seconds
#   recursive: 0.25846 seconds
# computing fib(1) to fib(30)
#   loopy:     0.00042 seconds
#   recursive: 2.83221 seconds