public void AddEdge(string name1, string name2, int length) { if (list.Contains(name1) && list.Contains(name2)) { Vertex first = list.GetVertex(name1); Vertex second = list.GetVertex(name2); if (list[first, second] == null) { Edge edge = new Edge(second, length); list.AddLink(first, edge); } } else { throw new VertexDoesNotExistException(); } }