fibs.rb

require 'benchmark'

def fib_vanilla(n)
  return n if (0..1).include?(n)
  fib_vanilla(n - 1) + fib_vanilla(n - 2)
end

fib_memoized = Hash.new { |numbers, index|
  numbers[index] = fib_memoized[index - 2] + fib_memoized[index - 1]
}.update(0 => 0, 1 => 1)

N = 40

Benchmark.bm do |x|
  x.report { fib_memoized[N] }
  x.report { fib_vanilla(N) }
end

#        user     system      total        real
#   0.000000   0.000000   0.000000 (  0.000044)
#  70.300000   0.050000  70.350000 ( 70.471916)