Powerset

powerset.rb

# my attempt
def powerset(set)
  all_sets = [[]]
  set.each do |elem|
    subsets = []
    all_sets.each do |subset|
      subsets << subset + [elem]
    end
    all_sets += subsets
  end
  all_sets
end

puts powerset([]).inspect
puts powerset([1]).inspect
puts powerset([1,2]).inspect
puts powerset([1,2,3]).inspect

# Pro version
# The Array power set is stolen from http://snippets.dzone.com/posts/show/3524
class Array
  # Returns the "power set" for this Array. This means that an array with all
  # subsets of the array's elements will be returned.
  def power_set
    # the power set line is stolen from http://johncarrino.net/blog/2006/08/11/powerset-in-ruby/
    inject([[]]) do |c,y|
      r=[]
      c.each do |i|
        r << i
        r << i + [y]
      end
      r
    end
  end
end

puts [1,2,3].power_set.inspect