Solution to Question 3 on the CS 10 W12 Final Exam

This is a solution that uses the Graph interface from the sixth edition to the 
textbook.  In W12 we used the fifth edition, which had a different Graph interface.

  /*
   * Sample solution to W12 final graph question
   * Finds the edges in a path given the vertices.
   * Precondition - verts is not an empty list.
   * @param verts a list containing the vertices in the path
   * @return the list of edges in the path
   * @throws IllegalStateException if not a valid path
   */
  public List<Edge<E>> getPath(List<Vertex<V>> verts) {
    List<Edge<E>> returnList = new ArrayList<Edge<E>>();
    Iterator<Vertex<V>> iter = verts.iterator();
    Vertex<V> first = iter.next();
    while(iter.hasNext()) {
      Vertex<V> second = iter.next();
      Edge<E> e = this.getEdge(first, second);
      if(e != null) {
        returnList.add(e);
        first = second;
      }
      else
        throw new IllegalStateException("Not a valid path");
    }
    return returnList;
  }