/**
* Returns the reverse of the digraph. 反向图
*
* @return the reverse of the digraph
*/
public Digraph reverse() { // 反向图
Digraph R = new Digraph(V);
for (int v = 0; v < V; v++) {
for (int w : adj(v)) { // 反向
R.addEdge(w, v);
}
}
return R;
}
/**
* Initializes a digraph from the specified input stream. The format is the number of vertices
* <em>V</em>, followed by the number of edges <em>E</em> , followed by <em>E</em> pairs of
* vertices, with each entry separated by whitespace.
*
* @param in the input stream
* @throws IndexOutOfBoundsException if the endpoints of any edge are not in prescribed range
* @throws IllegalArgumentException if the number of vertices or edges is negative
*/
public Digraph(In in) {
try {
this.V = in.readInt();
if (V < 0)
throw new IllegalArgumentException("Number of vertices in a Digraph must be nonnegative");
indegree = new int[V]; // 点
adj = (Bag<Integer>[]) new Bag[V];
for (int v = 0; v < V; v++) {
adj[v] = new Bag<Integer>();
}
int E = in.readInt(); // 边
if (E < 0)
throw new IllegalArgumentException("Number of edges in a Digraph must be nonnegative");
for (int i = 0; i < E; i++) {
int v = in.readInt();
int w = in.readInt();
addEdge(v, w);
}
} catch (NoSuchElementException e) {
throw new InputMismatchException("Invalid input format in Digraph constructor");
}
}