tasks a-s

Task/Power-set/Ruby/power-set.rb

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+# Based on http://johncarrino.net/blog/2006/08/11/powerset-in-ruby/
+# See the link if you want a shorter version. This was intended to show the reader how the method works.
+class Array
+  # Adds a power_set method to every array, i.e.: [1, 2].power_set
+  def power_set
+
+    # Injects into a blank array of arrays.
+    # acc is what we're injecting into
+    # you is each element of the array
+    inject([[]]) do |acc, you|
+
+      # Set up a new array to add into
+      ret = []
+
+      # For each array in the injected array,
+      acc.each do |i|
+
+        # Add itself into the new array
+        ret << i
+
+        # Merge the array with a new array of the current element
+        ret << i + [you]
+      end
+
+      # Return the array we're looking at to inject more.
+      ret
+
+    end
+
+  end
+
+  # A more functional and even clearer variant.
+  def func_power_set
+    inject([[]]) { |ps,item|    # for each item in the Array
+      ps +                      # take the powerset up to now and add
+      ps.map { |e| e + [item] } # it again, with the item appended to each element
+    }
+  end
+end
+
+#A direct translation of the "power array" version above
+class Set
+    def powerset
+        inject(Set[Set[]]) do |ps, item|
+            ps.union ps.map {|e| e.union (Set.new [item])}
+        end
+    end
+end