Complexity of Fixed Order Routing
摘要
We consider the classic Vehicle Routing Problem with the additional property that all requests are ordered and the subtour of each server (or vehicle) must obey the fixed order. A scheduling version of this problem was introduced by Bosman et al. (2019). We study several metric spaces and objective functions and our results show that in some settings such a fixed order simplifies the problem, while in others it makes an easy problem become \(\text {NP}\) -hard. For general metrics, we show that c-capacitated VRP remains APX-hard in the fixed order setting for \(c=3\) and show that the well-known iterated tour partitioning algorithm yields a \((2-1/c)\) -approximation. When all points are on the line, we show that the fixed order restriction makes VRP \(\text {NP}\) -hard to solve for minimizing total completion time or maximum completion time, in contrast to standard VRP. We also sketch how to obtain a PTAS in these settings for general metrics.