/**
* Initializes a new graph that is a deep copy of <tt>G</tt>.
*
* @param G the graph to copy
*/
public Graph(Graph G) {
this(G.V());
this.E = G.E();
for (int v = 0; v < G.V(); v++) {
// reverse so that adjacency list is in same order as original
Stack<Integer> reverse = new Stack<Integer>();
for (int w : G.adj[v]) {
reverse.push(w);
}
for (int w : reverse) {
adj[v].add(w);
}
}
}
/**
* Returns a random simple graph containing <tt>V</tt> vertices and <tt>E</tt> edges.
*
* @param V the number of vertices
* @param E the number of vertices
* @return a random simple graph on <tt>V</tt> vertices, containing a total of <tt>E</tt> edges
* @throws IllegalArgumentException if no such simple graph exists
*/
public static Graph simple(int V, int E) {
if (E > (long) V * (V - 1) / 2) // 简单图不含自环和平行边
throw new IllegalArgumentException("Too many edges");
if (E < 0) throw new IllegalArgumentException("Too few edges");
Graph G = new Graph(V);
SET<Edge> set = new SET<Edge>();
while (G.E() < E) { // 创建随机简单图
int v = StdRandom.uniform(V);
int w = StdRandom.uniform(V);
Edge e = new Edge(v, w);
if ((v != w) && !set.contains(e)) {
set.add(e);
G.addEdge(v, w);
}
}
return G;
}
/**
* Returns a random simple bipartite graph on <tt>V1</tt> and <tt>V2</tt> vertices with <tt>E</tt>
* edges.
*
* @param V1 the number of vertices in one partition
* @param V2 the number of vertices in the other partition
* @param E the number of edges
* @return a random simple bipartite graph on <tt>V1</tt> and <tt>V2</tt> vertices, containing a
* total of <tt>E</tt> edges
* @throws IllegalArgumentException if no such simple bipartite graph exists
*/
public static Graph bipartite(int V1, int V2, int E) {
if (E > (long) V1 * V2) throw new IllegalArgumentException("Too many edges");
if (E < 0) throw new IllegalArgumentException("Too few edges");
Graph G = new Graph(V1 + V2);
int[] vertices = new int[V1 + V2];
for (int i = 0; i < V1 + V2; i++) vertices[i] = i;
StdRandom.shuffle(vertices);
SET<Edge> set = new SET<Edge>();
while (G.E() < E) {
int i = StdRandom.uniform(V1);
int j = V1 + StdRandom.uniform(V2);
Edge e = new Edge(vertices[i], vertices[j]);
if (!set.contains(e)) {
set.add(e);
G.addEdge(vertices[i], vertices[j]);
}
}
return G;
}
public static int avgDegree(Graph G) {
return 2 * G.E() / G.V();
}
