gistfile1.rb

# why not?
def power(n)
  2 ** n
end

# if you must do it the brute force way
def power(n)
  return 1 if n == 0
  (1..[0,n-1].max).reduce(2) { |acc, n| acc * 2 }
end

# one could also write it recursively, but the above two would be most ruby-ish
# check http://ruby-doc.org/core-2.1.0/Enumerable.html#method-i-reduce