given k network routes from one source to one destination, and n files to be transfer from the source to the destination; each file fi has length li, the transfer speed along all k paths are identical. find out how to assign files to each of the k routes so that to finish the transfer of all n files in the shortest time. for example, given 10 files, their lengths are: 5, 6, 7, 3, 2, 10, 9, 8, 6, 4, and 3 paths, the optimal solution is to transfer them in 20/speed time unit.