Rezaul Alam Chowdhury Vijaya Ramachandran External-memory exact and approximate all-pairs shortest-paths in undirected graphs. 735-744 2005 conf/soda/2005 SODA http://doi.acm.org/10.1145/1070432.1070536 db/conf/soda/soda2005.html#ChowdhuryR05