source: branches/HeuristicLab.Algorithms.IteratedSentenceConstruction/HeuristicLab.Algorithms.IteratedSymbolicExpressionConstruction/3.3/Policies/DepthFirstSymbolicExpressionConstructionPolicy.cs @ 13042

using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Linq;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
using HeuristicLab.Random;

namespace HeuristicLab.Algorithms.IteratedSymbolicExpressionConstruction {
  [StorableClass]
  [Item("DepthFirstSymbolicExpressionConstructionPolicy", "Deterministic depth-first search (but tries terminal states first)")]
  public class DepthFirstSymbolicExpressionConstructionPolicy : SymbolicExpressionConstructionPolicyBase {

    public DepthFirstSymbolicExpressionConstructionPolicy()
      : base() {
    }

    protected override int Select(IReadOnlyList<object> followStates, IRandom random) {
      Contract.Assert(followStates.Any());
      int i = 0;
      foreach (var followState in followStates) {
        if ((bool)followState) return i;
        i++;
      }
      return 0; // return the first non-terminal follow state
    }

    public sealed override void Update(IEnumerable<object> stateSequence, double quality) {
      // ignore
    }

    protected override object CreateState(ISymbolicExpressionTreeNode root, List<ISymbol> actionSequence, ISymbolicExpressionTreeNode parent, int childIdx) {
      return parent.GetSubtree(childIdx).Symbol.MaximumArity == 0; // is it a terminal symbol?
    }

    #region IItem
    protected DepthFirstSymbolicExpressionConstructionPolicy(DepthFirstSymbolicExpressionConstructionPolicy original, Cloner cloner)
      : base(original, cloner) {
    }

    [StorableConstructor]
    protected DepthFirstSymbolicExpressionConstructionPolicy(bool deserializing) : base(deserializing) { }

    public override IDeepCloneable Clone(Cloner cloner) {
      return new DepthFirstSymbolicExpressionConstructionPolicy(this, cloner);
    }

    #endregion
  }
}