A Las Vegas approximation algorithm for metric $1$-median selection

Abstract: Given an $n$-point metric space, consider the problem of finding a point with the minimum sum of distances to all points. We show that this problem has a randomized algorithm that {\em always} outputs a $(2+\epsilon)$-approximate solution in an expected $O(n/\epsilon^2)$ time for each constant $\epsilon>0$. Inheriting Indyk's algorithm, our algorithm outputs a $(1+\epsilon)$-approximate $1$-median in $O(n/\epsilon^2)$ time with probability $\Omega(1)$.