source: trunk/sources/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Matching/SymbolicExpressionTreeMatching.cs @ 10562

Last change on this file since 10562 was 10562, checked in by bburlacu, 8 years ago

#2164: Committed initial version of the tree matching functionality.

File size: 2.4 KB
Line 
1using System;
2using System.Collections.Generic;
3using System.Linq;
4using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
5//using HeuristicLab.EvolutionTracking;
6
7namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
8  public static class SymbolicExpressionTreeMatching {
9    public static bool ContainsSubtree(this ISymbolicExpressionTreeNode root, ISymbolicExpressionTreeNode subtree, SymbolicExpressionTreeNodeSimilarityComparer comparer) {
10      return FindMatches(root, subtree, comparer).Any();
11    }
12    public static IEnumerable<ISymbolicExpressionTreeNode> FindMatches(ISymbolicExpressionTree tree, ISymbolicExpressionTreeNode subtree, SymbolicExpressionTreeNodeSimilarityComparer comparer) {
13      return FindMatches(tree.Root, subtree, comparer);
14    }
15
16    public static IEnumerable<ISymbolicExpressionTreeNode> FindMatches(ISymbolicExpressionTreeNode root, ISymbolicExpressionTreeNode subtree, SymbolicExpressionTreeNodeSimilarityComparer comp) {
17      var fragmentLength = subtree.GetLength();
18      // below, we use ">=" for Match(n, subtree, comp) >= fragmentLength because in case of relaxed conditions,
19      // we can have multiple matches of the same node
20
21      return root.IterateNodesBreadth().Where(n => n.GetLength() >= fragmentLength && Match(n, subtree, comp) == fragmentLength);
22    }
23
24    ///<summary>
25    /// Finds the longest common subsequence in quadratic time and linear space
26    /// Variant of:
27    /// D. S. Hirschberg. A linear space algorithm for or computing maximal common subsequences. 1975.
28    /// http://dl.acm.org/citation.cfm?id=360861
29    /// </summary>
30    /// <returns>Number of pairs that were matched</returns>
31    public static int Match(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b, SymbolicExpressionTreeNodeSimilarityComparer comp) {
32      if (!comp.Equals(a, b)) return 0;
33      int m = a.SubtreeCount;
34      int n = b.SubtreeCount;
35      if (m == 0 || n == 0) return 1;
36      var matrix = new int[m + 1, n + 1];
37      for (int i = 1; i <= m; ++i) {
38        var ai = a.GetSubtree(i - 1);
39        for (int j = 1; j <= n; ++j) {
40          var bj = b.GetSubtree(j - 1);
41          int match = Match(ai, bj, comp);
42          matrix[i, j] = Math.Max(Math.Max(matrix[i, j - 1], matrix[i - 1, j]), matrix[i - 1, j - 1] + match);
43        }
44      }
45      return matrix[m, n] + 1;
46    }
47  }
48}
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