public void addEdge(int v, int w) throws IllegalArgumentException {
        if (v < 0 || v >= numVertices || w < 0 || w >= numVertices)
            throw new IllegalArgumentException(
                "Out of range: v = " + v + ", w = " + w + ".");

	adjacentVertices[v] = w;
	Edge e = new Edge(v,w);
	edgeCosts[e] = NO_COST;

    }