Random Order Set Cover is as Easy as Offline

TL;DR

This paper presents a polynomial-time algorithm for online set cover with random element order, achieving near-optimal competitive ratios and extending to covering integer programs, thus bridging the gap between online and offline complexities.

Contribution

It introduces LearnOrCover, a novel multiplicative-weights-based algorithm that matches offline bounds in the random order online setting and extends to covering IPs.

Findings

Achieves $O(rac{ ext{log} mn}{})$ competitive ratio in random order online set cover.

Provides a new single-pass offline algorithm for set cover.

Extends results to solving pure covering integer programs in random order.

Abstract

We give a polynomial-time algorithm for OnlineSetCover with a competitive ratio of $O(\log mn)$ when the elements are revealed in random order, essentially matching the best possible offline bound of $O(\log n)$ and circumventing the $\Omega(\log m \log n)$ lower bound known in adversarial order. We also extend the result to solving pure covering IPs when constraints arrive in random order. The algorithm is a multiplicative-weights-based round-and-solve approach we call LearnOrCover. We maintain a coarse fractional solution that is neither feasible nor monotone increasing, but can nevertheless be rounded online to achieve the claimed guarantee (in the random order model). This gives a new offline algorithm for SetCover that performs a single pass through the elements, which may be of independent interest.