is_fib.rb

def fib_iterative(n)
  current = 0
  successor = 1

  n.times do |n|
    current, successor = successor, current + successor
  end

  return current
end


def fib_recursive(n)
  return  n  if n <= 1
  fib_recursive( n - 1 ) + fib_recursive( n - 2 )
end

def benchmark
  start = Time.now
  yield
  Time.now - start
end

#test code
puts fib_iterative(0) == 0
puts fib_iterative(1) == 1
puts fib_iterative(2) == 1
puts fib_iterative(3) == 2
puts fib_iterative(4) == 3
puts fib_iterative(5) == 5


puts fib_recursive(0) == 0
puts fib_recursive(1) == 1
puts fib_recursive(2) == 1
puts fib_recursive(3) == 2
puts fib_recursive(4) == 3
puts fib_recursive(5) == 5



puts "Recursive " +  benchmark {
  1000.times {fib_recursive(10)}
  }.to_s

puts "Iterative " + benchmark {
  1000.times {fib_iterative(10)}
  }.to_s