app/services/vns/engine.rb

@@ -2,6 +2,13 @@
 
 module VNS
   class Engine
+    class << self
+      def sequence(elements)
+        elements = elements.to_a
+        (elements + elements.reverse).chunk(&:itself).map(&:first)
+      end
+    end
+
     def target_function(&function)
       @target_function = function
     end
@@ -23,12 +30,12 @@ module VNS
 
       puts "Initial score: #{@best_score.to_f}"
 
-      @perturbations.each do |perturbation|
+      self.class.sequence(@perturbations).each do |perturbation|
         puts "Running perturbation: #{perturbation.name}"
         optimize(perturbation.new(@best_solution))
       end
 
-      @best_solution 
+      @best_solution
     end
 
     private

spec/services/vns/engine_spec.rb

@@ -0,0 +1,13 @@
+require 'rails_helper'
+
+module VNS
+  RSpec.describe Engine do
+    describe '.sequence' do
+      it { expect(described_class.sequence([])).to eq([]) }
+      it { expect(described_class.sequence([1])).to eq([1]) }
+      it { expect(described_class.sequence([1, 2])).to eq([1, 2, 1]) }
+      it { expect(described_class.sequence([1, 2, 3])).to eq([1, 2, 3, 2, 1]) }
+      it { expect(described_class.sequence([1, 2, 3, 4])).to eq([1, 2, 3, 4, 3, 2, 1]) }
+    end
+  end
+end