有向图----有向图的实现

public class Digraph {
	private int V;//顶点数
	private int E;//边数
	private Bag<Integer>[] adj;//邻接表
	public Digraph(int V) {
		this.V = V;
		adj = (Bag<Integer>[]) new Bag[V];
		for(int i=0;i<adj.length;i++)
			adj[i] = new Bag<Integer>();
	}

	public int V() {return V;}
	public int E() {return E;}
	public void addEdge(int v,int w) 
    { adj[v].add(w);	E++;}
    //顶点v所关联的所有顶点
	public Iterable<Integer> adj(int v){return adj[v];}
    //有向图的反转
	public Digraph reverse() {
		Digraph R = new Digraph(V);
		for(int v=0; v<V;v++) 
			for(int w : adj(v))
				R.addEdge(w, v);
		return R;
	}
}