【Algorithms IV】求解强连通分量 Kosaraju算法

public class KosarajuSCC {
    private boolean[] marked; // reached vertices
    private int[] id; // component identifiers
    private int count; // number of strong components

    public KosarajuSCC(Digraph G) {
        marked = new boolean[G.V()];
        id = new int[G.V()];

        DepthFirstOrder order = new DepthFirstOrder(G.reverse());
        for (int s : order.reversePost()) {
            if (!marked[s]) {
                dfs(G, s);
                count++;
            }
        }
    }

    private void dfs(Digraph G, int v) {
        marked[v] = true;
        id[v] = count;
        for (int w : G.adj(v))
            if (!marked[w])
                dfs(G, w);
    }

    public boolean stronglyConnected(int v, int w) {
        return id[v] == id[w];
    }

    public int id(int v) {
        return id[v];
    }

    public int count() {
        return count;
    }

    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            int N = in.nextInt();
            Digraph G = new Digraph(N);
            int E = in.nextInt();
            for (int i = 0; i < E; i++) {
                int p = in.nextInt();
                int q = in.nextInt();
                G.addEdge(p, q);
            }
            KosarajuSCC kj = new KosarajuSCC(G);
            log("" + kj.count());
        }
    }

    private static void log(String count2) {
        System.out.println(count2);
    }
}