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تسجيل مستخدم جديدNear-Optimal Decremental Hopsets with Applications
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Given a weighted undirected graph $G=(V,E,w)$, a hopset $H$ of hopbound $beta$ and stretch $(1+epsilon)$ is a set of edges such that for any pair of nodes $u, v in V$, there is a path in $G cup H$ of at most $beta$ hops, whose length is within a $(1+epsilon)$ factor from the distance between $u$ and $v$ in $G$. We show the first efficient decremental algorithm for maintaining hopsets with a polylogarithmic hopbound. The update time of our algorithm matches the best known static algorithm up to polylogarithmic factors. All the previous decremental hopset constructions had a superpolylogarithmic (but subpolynomial) hopbound of $2^{log^{Omega(1)} n}$ [Bernstein, FOCS09; HKN, FOCS14; Chechik, FOCS18]. By applying our decremental hopset construction, we get improved or near optimal bounds for several distance problems. Most importantly, we show how to decrementally maintain $(2k-1)(1+epsilon)$-approximate all-pairs shortest paths (for any constant $k geq 2)$, in $tilde{O}(n^{1/k})$ amortized update time and $O(k)$ query time. This significantly improves (by a polynomial factor) over the update-time of the best previously known decremental algorithm in the constant query time regime. Moreover, it improves over the result of [Chechik, FOCS18] that has a query time of $O(log log(nW))$, where $W$ is the aspect ratio, and the amortized update time is $n^{1/k}cdot(frac{1}{epsilon})^{tilde{O}(sqrt{log n})}$. For sparse graphs our construction nearly matches the best known static running time/ query time tradeoff.
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In the decremental Single-Source Shortest Path problem (SSSP), we are given a weighted directed graph $G=(V,E,w)$ undergoing edge deletions and a source vertex $r in V$; let $n = |V|, m = |E|$ and $W$ be the aspect ratio of the graph. The goal is to
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