Fix #61 - AlternatingPositionCrossover throw IndexOutOfRangeException

src/GeneticSharp.Domain.UnitTests/Crossovers/AlternatingPositionCrossoverTest.cs

@@ -13,7 +13,8 @@
 using GeneticSharp.Domain.Terminations;
 using System.Diagnostics;
 using GeneticSharp.Extensions.Tsp;
-
+using GeneticSharp.Domain.UnitTests.Crossovers.Issues;
+
 namespace GeneticSharp.Domain.UnitTests.Crossovers
 {
     [TestFixture]
@@ -165,5 +166,38 @@ public void GA_WithAlternatingPositionCrossover_Evolve()
                 population.Generations.First().BestChromosome.Fitness.Value,
                 population.Generations.Last().BestChromosome.Fitness.Value);
         }
+
+        /// <summary>
+        /// https://github.com/giacomelli/GeneticSharp/issues/61
+        /// </summary>
+        [Test]
+        public void GA_Issue61_Solved()
+        {
+            const Int32 FinalAns = 4567213;
+            var chromosome = new Issue61.GuessNumberChromosome(FinalAns.ToString().Length);
+            var population = new Population(1000, 5000, chromosome);
+            var fitness = new Issue61.GuessNumberFitness(FinalAns);
+            var selection = new EliteSelection();
+            var crossover = new AlternatingPositionCrossover();
+            var mutation = new ReverseSequenceMutation();
+            var ga = new GeneticAlgorithm(population, fitness, selection, crossover, mutation);
+            ga.MutationProbability = 0.2f;
+            ga.CrossoverProbability = 0.75f;
+            ga.Termination = new OrTermination(
+                new FitnessThresholdTermination(1.0),
+                new FitnessStagnationTermination(200),
+                new GenerationNumberTermination(1000));
+            ga.Population.GenerationStrategy = new TrackingGenerationStrategy();
+            ga.Start();
+
+            foreach(var gen in ga.Population.Generations)
+            {
+                foreach(var chromossome in gen.Chromosomes)
+                {
+                    // Asserts if AlternatingPositionCrossover generated only ordered chromossomes.
+                    Assert.AreEqual(chromosome.Length, chromosome.GetGenes().Distinct().Count());
+                }
+            }
+        }
     }
 }

src/GeneticSharp.Domain.UnitTests/Crossovers/Issues/Issue61.cs

@@ -0,0 +1,91 @@
+using GeneticSharp.Domain.Chromosomes;
+using GeneticSharp.Domain.Fitnesses;
+using GeneticSharp.Domain.Randomizations;
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace GeneticSharp.Domain.UnitTests.Crossovers.Issues
+{
+    public class Issue61
+    {
+        public class GuessNumberChromosome : ChromosomeBase
+        {
+
+            private const Int32 MaxGeneValue = 10;
+            private const Int32 MinGeneValue = 0;
+
+            public static int[] powof10 = new int[10] {
+            1,
+            10,
+            100,
+            1000,
+            10000,
+            100000,
+            1000000,
+            10000000,
+            100000000,
+            1000000000
+        };
+
+            private readonly Int32 numberDigits;
+
+            public GuessNumberChromosome(Int32 numberDigits) : base(numberDigits)
+            {
+                this.numberDigits = numberDigits;
+                var initGenes = RandomizationProvider.Current.GetUniqueInts(this.Length, MinGeneValue, MaxGeneValue);
+                for (int i = 0; i < this.Length; i++)
+                {
+                    this.ReplaceGene(i, new Gene(initGenes[i]));
+                }
+            }
+
+            public override IChromosome CreateNew()
+            {
+                return new GuessNumberChromosome(this.numberDigits);
+            }
+
+            public override Gene GenerateGene(int geneIndex)
+            {
+                return new Gene(RandomizationProvider.Current.GetInt(MinGeneValue, MaxGeneValue));
+            }
+
+            public Int32 ToGuessValue()
+            {
+                var genes = this.GetGenes();
+                return ToGuessValue(genes);
+            }
+
+            public static Int32 ToGuessValue(Gene[] genes)
+            {
+                int guessValue = 0;
+                for (int i = genes.Length - 1; i >= 0; i--)
+                {
+                    guessValue += ((Int32)genes[i].Value * powof10[i]);
+                }
+                return guessValue;
+            }
+        }
+
+        public class GuessNumberFitness : IFitness
+        {
+            private Int32 finalAns;
+            private Int32 maxDiffValue;
+
+            public GuessNumberFitness(Int32 finalAns)
+            {
+                this.finalAns = finalAns;
+                Int32 digits = this.finalAns.ToString().Length;
+                this.maxDiffValue = Math.Max(Math.Abs(this.finalAns - Int32.Parse(new string('9', digits))), this.finalAns);
+            }
+
+            public double Evaluate(IChromosome chromosome)
+            {
+                var genes = chromosome.GetGenes();
+                int guessValue = GuessNumberChromosome.ToGuessValue(genes);
+                double fitness = 1.0 - (Math.Abs(this.finalAns - guessValue) / (double)this.maxDiffValue);
+                return fitness;
+            }
+        }
+    }
+}

src/GeneticSharp.Domain/Crossovers/AlternatingPositionCrossover.cs

@@ -62,7 +62,10 @@ private IChromosome CreateChild(IChromosome firstParent, IChromosome secondParen
             for (int i = 0; i < firstParent.Length && childGenesIndex < firstParent.Length; i++)
             {
                 AddChildGene(childGenes, ref childGenesIndex, firstParent.GetGene(i));
-                AddChildGene(childGenes, ref childGenesIndex, secondParent.GetGene(i));
+
+                // The childGenesIndes could be incremented by the previous AddChildGene call
+                if (childGenesIndex < secondParent.Length)
+                    AddChildGene(childGenes, ref childGenesIndex, secondParent.GetGene(i));
             }
 
             child.ReplaceGenes(0, childGenes);