Class AHUUnrootedTreeIsomorphismInspector<V,​E>

  • Type Parameters:
    V - the type of the vertices
    E - the type of the edges
    All Implemented Interfaces:

    public class AHUUnrootedTreeIsomorphismInspector<V,​E>
    extends Object
    implements IsomorphismInspector<V,​E>
    This is an implementation of the AHU algorithm for detecting an (unweighted) isomorphism between two unrooted trees. Please see for a complete definition of the isomorphism problem for general graphs.

    The original algorithm was first presented in "Alfred V. Aho and John E. Hopcroft. 1974. The Design and Analysis of Computer Algorithms (1st ed.). Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA."

    This implementation runs in linear time (in the number of vertices of the input trees) while using a linear amount of memory.

    For an implementation that supports rooted trees see AHURootedTreeIsomorphismInspector.
    For an implementation that supports rooted forests see AHUForestIsomorphismInspector.

    Note: This inspector only returns a single mapping (chosen arbitrarily) rather than all possible mappings.

    Alexandru Valeanu
    • Constructor Detail

      • AHUUnrootedTreeIsomorphismInspector

        public AHUUnrootedTreeIsomorphismInspector​(Graph<V,​E> tree1,
                                                   Graph<V,​E> tree2)
        Construct a new AHU unrooted tree isomorphism inspector. Note: The constructor does NOT check if the input trees are valid.
        tree1 - the first tree
        tree2 - the second tree
        NullPointerException - if tree1 or tree2 is null
        IllegalArgumentException - if tree1 or tree2 is not undirected
        IllegalArgumentException - if tree1 or tree2 is empty
    • Method Detail

      • getMappings

        public Iterator<GraphMapping<V,​E>> getMappings()
        Get an iterator over all calculated (isomorphic) mappings between two graphs.
        Specified by:
        getMappings in interface IsomorphismInspector<V,​E>
        an iterator over all calculated (isomorphic) mappings between two graphs
      • isomorphismExists

        public boolean isomorphismExists()
        Check if an isomorphism exists.
        Specified by:
        isomorphismExists in interface IsomorphismInspector<V,​E>
        true if there is an isomorphism, false if there is no isomorphism
      • getMapping

        public IsomorphicGraphMapping<V,​E> getMapping()
        Get an isomorphism between the input trees or null if none exists.
        isomorphic mapping, null is none exists