O(1)-Approximations for Maximum Movement Problems

We develop constant-factor approximation algorithms for minimizing the maximum movement made by pebbles on a graph to reach a configuration in which the pebbles form a connected subgraph (connectivity), or interconnect a constant number of stationary nodes (Steiner tree). These problems model the minimization of the total time required to reconfigure a robot swarm to achieve a proximity (e.g., radio) network with these connectivity properties. Our approximation factors are tight up to constant factors, as none of these problems admit a (2− ε)-approximation assuming P 6= NP.