$(1-ε)$-approximate fully dynamic densest subgraph: linear space and faster update time

We consider the problem of maintaining a $(1-\epsilon)$-approximation to the densest subgraph (DSG) in an undirected multigraph as it undergoes edge insertions and deletions (the fully dynamic setting). Sawlani and Wang [SW20] developed a data structure that, for any given $\epsilon > 0$, maintains a $(1-\epsilon)$-approximation with $O(\log⁴ n/\epsilon^6)$ worst-case update time for edge operations, and $O(1)$ query time for reporting the density value. Their data structure was the first to achieve near-optimal approximation, and improved previous work that maintained a $(1/4 - \epsilon)$ approximation in amortized polylogarithmic update time [BHNT15]. In this paper we develop a data structure for $(1-\epsilon)$-approximate DSG that improves the one from [SW20] in two aspects. First, the data structure uses linear space improving the space bound in [SW20] by a logarithmic factor. Second, the data structure maintains a $(1-\epsilon)$-approximation in amortized $O(\log² n/\epsilon^4)$ time per update while simultaneously guaranteeing that the worst case update time is $O(\log³ n \log \log n/\epsilon^6)$. We believe that the space and update time improvements are valuable for current large scale graph data sets. The data structure extends in a natural fashion to hypergraphs and yields improvements in space and update times over recent work [BBCG22] that builds upon [SW20].