Efficient exponential time algorithms for edit distance between unordered trees

Abstract

This paper presents efficient exponential time algorithms for the unordered tree edit distance problem, which is known to be NP-hard. For a general case, an time algorithm is presented, where n 1 and n 2 are the numbers of nodes in two input trees. This algorithm is obtained by a combination of dynamic programming, exhaustive search, and maximum weighted bipartite matching. For bounded degree trees over a fixed alphabet, it is shown that the problem can be solved in time for any fixed ε > 0. This result is achieved by avoiding duplicate calculations for identical subsets of small subtrees. © 2012 Springer-Verlag.