1. In a directed acyclic graph G, define a vertex v to be "final" if there exists a topological ordering in which v is the last vertex in the ordering. Describe a simple linear time algorithm that takes as input a directed acyclic graph, and produces as output a list of all of the final vertices in G. Your algorithm is only required to work correctly on acyclic graphs; if the graph is not acyclic, any output (or crashing) is acceptable. Your description may either be in English or pseudocode