source: branches/2886_SymRegGrammarEnumeration/HeuristicLab.Algorithms.DataAnalysis.SymRegGrammarEnumeration/Hashing/Hasher.cs @ 16022

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using HeuristicLab.Common;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;

namespace HeuristicLab.Algorithms.DataAnalysis.SymRegGrammarEnumeration.GrammarEnumeration {
  [StorableClass]
  public abstract class Hasher<THashType> : DeepCloneable {
    protected Hasher(Grammar grammar) {
      Grammar = grammar;
    }

    protected Hasher(Hasher<THashType> original, Cloner cloner) : base(original, cloner) {
      Grammar = cloner.Clone(original.Grammar);
    }

    [Storable]
    protected Grammar Grammar { get; private set; }

    protected abstract THashType AggregateHashes(Symbol operatorSym, IList<THashType> hashes);

    public int CalcHashCode(SymbolString sentence) {
      Debug.Assert(sentence.Any(), "Trying to evaluate empty sentence!");

      Stack<Symbol> parseStack = new Stack<Symbol>(sentence);

      Symbol peek = parseStack.Peek();
      return AggregateHashes(peek, GetSubtreeHashes(parseStack)).GetHashCode();
    }

    [StorableConstructor]
    protected Hasher(bool deserializing) { }

    private IList<THashType> GetSubtreeHashes(Stack<Symbol> parseStack) {
      Symbol currentSymbol = parseStack.Pop();

      // ADDITION
      if (currentSymbol == Grammar.Addition) {
        return GetAdditionSubtreeHashes(parseStack);
      }

      // MULTIPLICATION
      if (currentSymbol == Grammar.Multiplication) {
        return GetMultiplicationSubtreeHashes(parseStack);
      }

      // LOG, EXP, SIN, INV
      if (currentSymbol == Grammar.Log || currentSymbol == Grammar.Exp ||
          currentSymbol == Grammar.Sin || currentSymbol == Grammar.Inv) {
        // Directly aggregate the single subtree
        return new[] { AggregateHashes(parseStack.Peek(), GetSubtreeHashes(parseStack)) };
      }

      // var, const or nonterminal symbol
      return new[] { AggregateHashes(currentSymbol, new THashType[0]) };
    }

    private void AddAdditionChildHashes(HashSet<THashType> hashSet, Stack<Symbol> symbolStack) {
      var peek = symbolStack.Peek();
      var hashes = GetSubtreeHashes(symbolStack); // will pop the stack

      if (peek == Grammar.Addition)
        hashSet.UnionWith(hashes);
      else
        hashSet.Add(AggregateHashes(peek, hashes));
    }

    private IList<THashType> GetAdditionSubtreeHashes(Stack<Symbol> parseStack) {
      var uniqueChildHashes = new HashSet<THashType>();

      AddAdditionChildHashes(uniqueChildHashes, parseStack); // first child 
      AddAdditionChildHashes(uniqueChildHashes, parseStack); // second child 

      var result = uniqueChildHashes.ToArray();
      Array.Sort(result);
      return result;
    }

    private void AddMultiplicationChildHashes(List<THashType> hashList, Stack<Symbol> symbolStack) {
      var peek = symbolStack.Peek();
      var hashes = GetSubtreeHashes(symbolStack);
      if (peek == Grammar.Multiplication)
        hashList.AddRange(hashes);
      else
        hashList.Add(AggregateHashes(peek, hashes));
    }

    public IList<THashType> GetMultiplicationSubtreeHashes(Stack<Symbol> parseStack) {
      var childHashes = new List<THashType>();

      AddMultiplicationChildHashes(childHashes, parseStack); // first child
      AddMultiplicationChildHashes(childHashes, parseStack); // second child

      // Sort due to commutativity
      childHashes.Sort();

      if (childHashes.Count <= 2)
        return childHashes;

      // Cancel out inverse factors.
      var isInvFactor = new bool[childHashes.Count];
      bool foundInvFactor = false;
      for (int i = 0; i < isInvFactor.Length; i++) {
        if (isInvFactor[i]) continue;

        var currFactor = childHashes[i];
        var invFactor = AggregateHashes(Grammar.Inv, new[] { currFactor });

        int indexOfInv = childHashes.IndexOf(invFactor);
        if (indexOfInv >= 0 && !isInvFactor[indexOfInv]) {
          isInvFactor[i] = isInvFactor[indexOfInv] = true;
          foundInvFactor = true;
        }
      }

      if (!foundInvFactor)
        return childHashes;

      return childHashes
        .Where((c, i) => !isInvFactor[i])
        .ToArray();
    }
  }

  [StorableClass]
  public class IntHasher : Hasher<int> {
    public IntHasher(Grammar grammar) : base(grammar) { }

    public IntHasher(IntHasher original, Cloner cloner) : base(original, cloner) { }

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

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

    protected override int AggregateHashes(Symbol operatorSym, IList<int> hashes) {
      int start;
      if ((operatorSym == Grammar.Addition || operatorSym == Grammar.Multiplication) && hashes.Count <= 1) {
        start = 0;

      } else if (operatorSym is NonterminalSymbol || operatorSym is VariableTerminalSymbol) {
        return operatorSym.StringRepresentation.GetHashCode();

      } else {
        start = operatorSym.StringRepresentation.GetHashCode();
      }

      for (int i = 0; i < hashes.Count; i++) {
        start = ((start << 5) + start) ^ hashes[i];
      }
      return start;
    }
  }

  [StorableClass]
  public class StringHasher : Hasher<string> {
    public StringHasher(Grammar grammar) : base(grammar) { }

    public StringHasher(StringHasher original, Cloner cloner) : base(original, cloner) { }

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

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

    protected override string AggregateHashes(Symbol operatorSym, IList<string> hashes) {
      var hashesArray = hashes.ToArray();

      if ((operatorSym == Grammar.Addition || operatorSym == Grammar.Multiplication) && hashesArray.Length <= 1) {
        return hashesArray[0];
      }
      if (operatorSym is NonterminalSymbol || operatorSym is VariableTerminalSymbol) {
        return operatorSym.StringRepresentation;
      }

      return $"[{operatorSym.StringRepresentation} ° {string.Join(" ° ", hashesArray)}]";
    }
  }
}