Algorithms

4.2 ■ Directed Graphs
569
Directed graph (digraph) data type
public class Digraph
{
private final int V;
private int E;
private Bag[] adj;
}
public Digraph(int V)
{
this.V = V;
this.E = 0;
adj = (Bag[]) new Bag[V];
for (int v = 0; v < V; v++)
adj[v] = new Bag();
}
public int V() { return V; }
public int E() { return E; }
public void addEdge(int v, int w)
{
adj[v].add(w);
E++;
}
public Iterable adj(int v)
{ return adj[v]; }
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;
}
This Digraph data type is identical to Graph (page 526) except
that addEdge() only calls add() once, and it has an
instance method reverse() that returns a copy with all
its edges reversed. Since the code is easily derived from the
corresponding code for Graph, we omit the toString()
method (see the table on page 523) and the input stream constructor
from (see page 526).
V
tinyDG.txt
13
22
4 2
2 3
3 2
6 0
0 1
2 0
11 12
12 9
9 10
9 11
8 9
10 12
11 4
4 3
3 5
7 8
8 7
5 4
0 5
6 4
6 9
7 6
0
1
2
3
4
5
6
7
8
9
10
11
12
adj[]
E
5 1
0 3
5 2
3 2
4
9 4 0
6 8
7 9
11 10
12
4 12
Digraph input format and
adjacency-lists representation
9