CC.java

Below is the syntax highlighted version of CC.java from §4.1 Undirected Graphs.

/*************************************************************************
 *  Compilation:  javac CC.java
 *  Execution:    java CC filename.txt
 *  Dependencies: Graph.java StdOut.java Queue.java
 *  Data files:   http://algs4.cs.princeton.edu/41undirected/tinyG.txt
 *
 *  Compute connected components using depth first search.
 *  Runs in O(E + V) time.
 *
 *  %  java CC tinyG.txt
 *  3 components
 *  0 1 2 3 4 5 6
 *  7 8 
 *  9 10 11 12
 *
 *************************************************************************/

public class CC {
    private boolean[] marked;   // marked[v] = has vertex v been marked?
    private int[] id;           // id[v] = id of connected component containing v
    private int[] size;         // size[id] = number of vertices in given component
    private int count;          // number of connected components

    public CC(Graph G) {
        marked = new boolean[G.V()];
        id = new int[G.V()];
        size = new int[G.V()];
        for (int v = 0; v < G.V(); v++) {
            if (!marked[v]) {
                dfs(G, v);
                count++;
            }
        }
    }

    // depth first search
    private void dfs(Graph G, int v) {
        marked[v] = true;
        id[v] = count;
        size[count]++;
        for (int w : G.adj(v)) {
            if (!marked[w]) {
                dfs(G, w);
            }
        }
    }

    // id of connected component containing v
    public int id(int v) {
        return id[v];
    }

    // size of connected component containing v
    public int size(int v) {
        return size[id[v]];
    }

    // number of connected components
    public int count() {
        return count;
    }

    // are v and w in the same connected component?
    public boolean areConnected(int v, int w) {
        return id(v) == id(w);
    }


    // test client
    public static void main(String[] args) {
        In in = new In(args[0]);
        Graph G = new Graph(in);
        CC cc = new CC(G);

        // number of connected components
        int M = cc.count();
        StdOut.println(M + " components");

        // compute list of vertices in each connected 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[cc.id(v)].enqueue(v);
        }

        // print results
        for (int i = 0; i < M; i++) {
            for (int v : components[i]) {
                StdOut.print(v + " ");
            }
            StdOut.println();
        }
    }
}