Avrim Blum Shuchi Chawla David R. Karger Terran Lane Adam Meyerson Maria Minkoff Approximation Algorithms for Orienteering and Discounted-Reward TSP. 653-670 2007 37 SIAM J. Comput. 2 http://dx.doi.org/10.1137/050645464 db/journals/siamcomp/siamcomp37.html#BlumCKLMM07