Separator Based Sparsification. I. Planary Testing and Minimum Spanning Trees

We describe algorithms and data structures for maintaining a dynamic planar graph subject to edge insertions and edge deletions that preserve planarity but that can change the embedding. We give a fully dynamic planarity testing algorithm that maintains a graph subject to edge insertions and deletions and that allows queries that test whether the graph is currently planar, or whether a potential new edge would violate planarity, in O(n ) amortized time per update or query. We give fully dynamic algorithms for maintaining the connected components, the best swap and the minimum spanning forest of a planar graph in O(log n) worst-case time per insertion and O(log n) per deletion. Finally, we give fully dynamic algorithms for maintaining the 2-edge-connected components of a planar graph in O(log n) amortized time per insertion and O(log n) per deletion. All of the data structures, except for the one that answers planarity queries, handle only insertions that keep the graph planar. All our algorithms improve previous bounds. The improvements are based upon a new type of sparsification combined with several properties of separators in planar graphs. ] 1996 Academic Press, Inc.