  The Multiple Drone-Delivery Scheduling Problem (MDSP) is a scheduling problem
that optimizes the maximum reward earned by a set of $m$ drones executing a
sequence of deliveries on a truck delivery route. The current best-known
approximation algorithm for the problem is a $\frac{1}{4}$-approximation
algorithm developed by Jana and Mandal (2022). In this paper, we propose exact
and approximation algorithms for the general MDSP, as well as a unit-cost
variant. We first propose a greedy algorithm which we show to be a
$\frac{1}{3}$-approximation algorithm for the general MDSP problem formulation,
provided the number of conflicting intervals is less than the number of drones.
We then introduce a unit-cost variant of MDSP and we devise an exact dynamic
programming algorithm that runs in polynomial time when the number of drones
$m$ can be assumed to be a constant.
