Deterministic Fully Dynamic SSSP and More

TL;DR

This paper introduces the first deterministic fully dynamic algorithms for maintaining exact single-source shortest paths, reachability, and approximate all-pairs distances in unweighted directed graphs, resolving longstanding open problems.

Contribution

It presents the first non-trivial deterministic algorithms for fully dynamic exact SSSP, reachability, and approximate all-pairs distances in unweighted directed graphs.

Findings

First deterministic fully dynamic exact SSSP algorithm.

First deterministic subquadratic reachability data structure.

First deterministic sub-$n^ ext{omega}$ approximate all-pairs distances data structure.

Abstract

We present the first non-trivial fully dynamic algorithm maintaining exact single-source distances in unweighted graphs. This resolves an open problem stated by Sankowski [COCOON 2005] and van den Brand and Nanongkai [FOCS 2019]. Previous fully dynamic single-source distances data structures were all approximate, but so far, non-trivial dynamic algorithms for the exact setting could only be ruled out for polynomially weighted graphs (Abboud and Vassilevska Williams, [FOCS 2014]). The exact unweighted case remained the main case for which neither a subquadratic dynamic algorithm nor a quadratic lower bound was known. Our dynamic algorithm works on directed graphs, is deterministic, and can report a single-source shortest paths tree in subquadratic time as well. Thus we also obtain the first deterministic fully dynamic data structure for reachability (transitive closure) with subquadratic update and query time. This answers an open problem of van den Brand, Nanongkai, and Saranurak [FOCS 2019]. Finally, using the same framework we obtain the first fully dynamic data structure maintaining all-pairs $(1+\epsilon)$-approximate distances within non-trivial sub-$n^\omega$ worst-case update time while supporting optimal-time approximate shortest path reporting at the same time. This data structure is also deterministic and therefore implies the first known non-trivial deterministic worst-case bound for recomputing the transitive closure of a digraph.