MPI-I-95-1-013

The problem of finding an implicit representation for a graph such that vertex adjacency can be tested quickly is fundamental to all graph algorithms. In particular, it is possible to represent sparse graphs on $n$ vertices using $O(n)$ space such that vertex adjacency is tested in $O(1)$ time. We show here how to construct such a representation efficiently by providing simple and optimal algorithms, both in a sequential and a parallel setting. Our sequential algorithm runs in $O(n)$ time. The parallel algorithm runs in $O(\log n)$ time using $O(n/{\log n})$ CRCW PRAM processors, or in $O(\log n\log^*n)$ time using $O(n/\log n\log^*n)$ EREW PRAM processors. Previous results for this problem are based on matroid partitioning and thus have a high complexity.