Computing minimal spanning subgraphs in linear time

Let P be a property of undirected graphs. We consider the following problem: given a graph G that has property P, find a minimal spanning subgraph of G with property P. We describe two related algorithms for this problem and prove their correctness under some rather weak assumptions about P. We devise a general technique for analyzing the worst-case behavior of these algorithms. By applying the technique to 2-edge-connectivity and biconnectivity, we obtain an ω(m + n log n) lower bound on the worst-case running time of the algorithms for these two properties, thus settling open questions posed earlier with regard to these properties. We then describe refinements of the basic algorithms that yield the first linear-time algorithms for finding a minimal 2-edge-connected spanning subgraph and a minimal biconnected spanning subgraph of a graph.