
In this paper, we consider the Program Download Problem (PDP) which is to download a set of desired programs from multiple channels. When the problem is to decide whether the download can be done by a given deadline $$d$$ d and each program appears in each of the $$n$$ n channels at most once, denoted as $$\textit{PDP}(n,1,d)$$ PDP ( n , 1 , d ) , we prove that $$\textit{PDP}(n,1,d)$$ PDP ( n , 1 , d ) is NP-complete by a reduction from 3-SAT(3). We can extend the NP-hardness proof to $$\textit{PDP}(2,3,d)$$ PDP ( 2 , 3 , d ) where there are only two channels but each program could appear in each channel at most 3 times, although $$\textit{PDP}(2,1,d)$$ PDP ( 2 , 1 , d ) and $$\textit{PDP}(2,2,d)$$ PDP ( 2 , 2 , d ) are both in P. We show that the aligned version of the problem (APDP) is polynomially solvable by reducing it to a maximum flow problem. For a different version of the problem, MPDP, where the objective is to maximize the number of program downloaded before a given deadline $$d$$ d , we prove that it is fixed-parameter tractable. Finally, we devise an approximation algorithm for $$\textit{MPDP}(2,p,d),\,p\ge 3$$ MPDP ( 2 , p , d ) , p ? 3 , which aims to maximize the number of desired programs downloaded in two channels.
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