/*

* Sample usage: java Digraph tinyDG.txt

* Sample usage: java Digraph mediumDG.txt

*/

public class Digraph {

private final int V; // number of vertices

private int E; // number of edges

private LinkedBag<Integer>[] adj; // adjacency lists

public Digraph(int V){

this.V = V;

this.E = 0;

adj = (LinkedBag<Integer>[]) new LinkedBag[V]; // Create array of lists

for (int v = 0; v < V; v++) // Initialize all lists to empty

adj[v] = new LinkedBag<Integer>();

}

public Digraph(In in){

this(in.readInt()); // read V and construct this graph

int E = in.readInt(); // read E

for (int i=0; i<E; i++){

// Add an edge

int v = in.readInt(); // read a vertex

int w = in.readInt(); // read another vertex

addEdge(v, w); // add edge connecting them

}

}

public int V(){

return V;

}

public int E(){

return E;

}

public void addEdge(int v, int w){

adj[v].add(w); // add w to v's list

E++;

}

public Iterable<Integer> adj(int v){

return adj[v];

}

public String toString(){

String s = V + " vertices, " + E + " edges\n";

for (int v=0; v < V; v++){

s += v + ": ";

for (int w : this.adj[v])

s += w + " ";

s += "\n";

}

return s;

}

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;

}

public static void main(String[] args){

In in = new In(args[0]);

Digraph G = new Digraph(in);

StdOut.println(G);

}

}