/** Unit tests the <tt>GabowSCC</tt> data type. */
public static void main(String[] args) {
In in = new In(args[0]);
Digraph G = new Digraph(in);
GabowSCC scc = new GabowSCC(G);
// number of connected components
int M = scc.count();
StdOut.println(M + " components");
// compute list of vertices in each strong component
Queue<Integer>[] components = (Queue<Integer>[]) new Queue[M];
for (int i = 0; i < M; i++) {
components[i] = new Queue<Integer>();
}
for (int v = 0; v < G.V(); v++) {
components[scc.id(v)].enqueue(v);
}
// print results
for (int i = 0; i < M; i++) {
for (int v : components[i]) {
StdOut.print(v + " ");
}
StdOut.println();
}
}
/** Unit tests the <tt>DepthFirstOrder</tt> data type. */
public static void main(String[] args) {
In in = new In(args[0]);
Digraph G = new Digraph(in);
DepthFirstOrder dfs = new DepthFirstOrder(G);
StdOut.println(" v pre post");
StdOut.println("--------------");
for (int v = 0; v < G.V(); v++) {
StdOut.printf("%4d %4d %4d\n", v, dfs.pre(v), dfs.post(v));
}
StdOut.print("Preorder: ");
for (int v : dfs.pre()) {
StdOut.print(v + " ");
}
StdOut.println();
StdOut.print("Postorder: ");
for (int v : dfs.post()) {
StdOut.print(v + " ");
}
StdOut.println();
StdOut.print("Reverse postorder: ");
for (int v : dfs.reversePost()) {
StdOut.print(v + " ");
}
StdOut.println();
}
/**
* Determines a depth-first order for the digraph <tt>G</tt>.
*
* @param G the digraph
*/
public DepthFirstOrder(Digraph G) {
pre = new int[G.V()];
post = new int[G.V()];
postorder = new Queue<Integer>();
preorder = new Queue<Integer>();
marked = new boolean[G.V()];
for (int v = 0; v < G.V(); v++) if (!marked[v]) dfs(G, v);
}
// does the id[] array contain the strongly connected components?
private boolean check(Digraph G) {
TransitiveClosure tc = new TransitiveClosure(G);
for (int v = 0; v < G.V(); v++) {
for (int w = 0; w < G.V(); w++) {
if (stronglyConnected(v, w) != (tc.reachable(v, w) && tc.reachable(w, v))) return false;
}
}
return true;
}
/**
* Computes the strong components of the digraph <tt>G</tt>.
*
* @param G the digraph
*/
public GabowSCC(Digraph G) {
marked = new boolean[G.V()];
stack1 = new Stack<Integer>();
stack2 = new Stack<Integer>();
id = new int[G.V()];
preorder = new int[G.V()];
for (int v = 0; v < G.V(); v++) id[v] = -1;
for (int v = 0; v < G.V(); v++) {
if (!marked[v]) dfs(G, v);
}
// check that id[] gives strong components
assert check(G);
}
// run DFS in digraph G from vertex v and compute preorder/postorder
private void dfs(Digraph G, int v) {
marked[v] = true;
pre[v] = preCounter++;
preorder.enqueue(v);
for (int w : G.adj(v)) {
if (!marked[w]) {
dfs(G, w);
}
}
postorder.enqueue(v);
post[v] = postCounter++;
}
private void dfs(Digraph G, int v) {
marked[v] = true;
preorder[v] = pre++;
stack1.push(v);
stack2.push(v);
for (int w : G.adj(v)) {
if (!marked[w]) dfs(G, w);
else if (id[w] == -1) {
while (preorder[stack2.peek()] > preorder[w]) stack2.pop();
}
}
// found strong component containing v
if (stack2.peek() == v) {
stack2.pop();
int w;
do {
w = stack1.pop();
id[w] = count;
} while (w != v);
count++;
}
}
