Example of fast fibonacci algorithm in Ruby

fast_fib.rb

# Cribbed from https://stackoverflow.com/questions/24438655/ruby-fibonacci-algorithm
def fib_memo(n, memo)
  memo[n] ||= fib_memo(n-1, memo) + fib_memo(n-2, memo)
end

def fib(n)
  raise "fib not defined for negative numbers" if n < 0
  fib_memo(n, [0, 1])
end

def timer
  n = Time.now
  yield
  puts "#{(Time.now - n) * 1_000}ms"
end

timer { fib(42) } # 0.013ms on my laptop