fib.rb

def fib2(n)
  return n if n == 0 || n == 1
  f = (0..n).to_a
  f[0] = 0, f[1] = 1
  i = 2
  while i < n
    f[i] = f[i-1] + f[i-2]
    return f[i]
    i += 1
  end
end

puts fib2(10)