# Approximation and Parameterized Complexity of Minimax Approval Voting

We present three results on the complexity of Minimax Approval Voting that is a voting rule for choosing committee of fixed size k. Here, we see the votes and the choice as 0-1 strings of length m (characteristic vertors of the subsets). The goal is to minimize the maximum Hamming distance to a vote. First, we study Minimax Approval Voting parameterized by the Hamming distance d from the solution to the votes. We show Minimax Approval Voting admits no algorithm running in time O*(2^o(d\log d)), unless the Exponential Time Hypothesis (ETH) fails. This means that the O*(d^(2d)) algorithm of Misra et al. [AAMAS 2015] is essentially optimal. Motivated by this, we then show a parameterized approximation scheme, running in time O*((3/eps)^(2d)), which is essentially tight assuming ETH. Finally, we get a new polynomial-time randomized approximation scheme for Minimax Approval Voting, which runs in time n^O(log(1/eps)/eps^2) * poly(m), almost matching the running time of the fastest known PTAS for Closest String due to Ma and Sun [SIAM J. Comp. 2009].

Authors: Marek Cygan, Łukasz Kowalik, Arkadiusz Socała, Krzysztof Sornat