Before revision:  First, we consider a unidirectional problem where a resource can only be allocated to a user located to its leftas exemplified here. Imagine a one-way city street with traffic flowing from right to left; a ride-sharing company has distributed its vehicles along the street, which are ready to pick up users waiting at various locations. Users equipped with smartphone ride-hailing apps can register their requests on a ride allocation system. The latter then attempts to service each user by assigning a vehicle with spare capacity located to the user's right such that the average "pick up" distance is minimized.
After revision:  First, we consider unidirectional assignment policies that allocate resources only to users located to their left.