A fast algorithm for optimal alignment between similar ordered trees

  • Authors:

  • Jesper Jansson;Andrzej Lingas

  • Affiliations:

  • Department of Computer Science, Lund University, Box 118, SE-221 00 Lund, Sweden;Department of Computer Science, Lund University, Box 118, SE-221 00 Lund, Sweden

  • Venue:
  • Fundamenta Informaticae - Special issue on computing patterns in strings
  • Year:
  • 2002

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Abstract

We present a fast algorithm for optimal alignment between two similar ordered trees with node labels. Let S and T be two such trees with |S| and |T| nodes, respectively. If there exists an optimal alignment between S and T which uses at most d blank symbols and d is known in advance, it can be constructed in O(n log n. (maxdeg)3 . d2) time, where n = max{|S|, |T|} and maxdeg is the maximum degree of all nodes in S and T. If d is not known in advance, we can construct an optimal alignment in O(n log n. (maxdeg)3. f2) time, where f is the difference between the highest possible score for any alignment between two trees having a total of |S| + |T| nodes and the score of an optimal alignment between S and T, if the scoring scheme satisfies some natural assumptions. In particular, if the degrees of both input trees are bounded by a constant, the running times reduce to O(n log n . d2) and O(n log n. f2), respectively.