memo_ruby_fib.rb

def fib(n)
  return n if n < 2
  
  # ruby has implicit returns
  # so no need to say return on the last line here
  fib(n - 1) + fib(n - 2)
end

def memo_fib(n, cache = {})
  return n if n < 2
  # same return rule applies here
  # we either return existing cache, or add a new key/value
  cache[n] ||= fib(n - 1, cache) + fib(n - 2, cache)
end