aff.rb

# fibo O(n)

CACHE = {}

def fib(n)
  raise ArgumentError if n < 0

  if CACHE[n]
    CACHE[n]
  else
    CACHE[n] = if n == 0 || n == 1
                 1
               else
                 fib(n-1) + fib(n -2)
               end
  end
end

(1..30).each do |n|
  puts "#{n} => #{fib(n)}"
end