only store unique programs

genetic.rb

@@ -33,6 +33,7 @@ def main
         p2.mutate
         [grade_program(p2), p2]
       end
+      programs.uniq!
       programs.sort! do |a, b|
         a.first <=> b.first
       end

program.rb

@@ -1,4 +1,6 @@
 class Program
+  include Comparable
+
   def initialize
     @instructions = []
     (2 + rand(4)).times do
@@ -60,6 +62,18 @@ class Program
     @instructions.size
   end
 
+  def <=>(other)
+    @instructions <=> other.instance_variable_get(:@instructions)
+  end
+
+  def eql?(other)
+    (other.class == self.class) && (other == self)
+  end
+
+  def hash
+    @instructions.hash
+  end
+
 private
 
   def random_instruction