30. In the implementation for a breadth-first search we studied, a queue was used. The code below replaces the queue with a stack. List the pre-order enumeration that the vertices in the graph below are visited using this modified method, starting from vertex 0. 3 6 modSearch: /** stack-based search */ static void modSearch (Graph G, int start) { Stack S = new AStack (G.n()); S.push(start); G.setMark (start, VISITED); while (S.length() > 0) { int v S.pop(); PreVisit (G, v); for (int w = G.first (v)%3B w < G.n(); w = G.next(v, w)) if (G.getMark (w) == UNVISITED) { G.setMark (w, VISITED); S.push(w); } } }