Do not copy others.

Consider a directed graph G = (V, E) that captures the road network in your city. You live at vertex s V . Each edge e has a positive length l(e) > 0. Further, there are gift stores at a subset S V of vertices. Your friends live at another subset F V of vertices. For each vertex v in F, you would like to know the shortest path from s to v stopping by at least one gift stores on its way. Design an algorithm for this problem, and analyze its correctness and running time.