DirectedDFS.java


Below is the syntax highlighted version of DirectedDFS.java.


/******************************************************************************
 *  Compilation:  javac DirectedDFS.java
 *  Execution:    java DirectedDFS digraph.txt s
 *  Dependencies: Digraph.java Bag.java In.java StdOut.java
 *  Data files:   http://algs4.cs.princeton.edu/42digraph/tinyDG.txt
 *                http://algs4.cs.princeton.edu/42digraph/mediumDG.txt
 *                http://algs4.cs.princeton.edu/42digraph/largeDG.txt
 *
 *  Determine single-source or multiple-source reachability in a digraph
 *  using depth first search.
 *  Runs in O(E + V) time.
 *
 *  % java DirectedDFS tinyDG.txt 1
 *  1
 *
 *  % java DirectedDFS tinyDG.txt 2
 *  0 1 2 3 4 5
 *
 *  % java DirectedDFS tinyDG.txt 1 2 6
 *  0 1 2 3 4 5 6 8 9 10 11 12 
 *
 ******************************************************************************/

package edu.princeton.cs.algs4;
/**
 *  The {@code DirectedDFS} class represents a data type for 
 *  determining the vertices reachable from a given source vertex <em>s</em>
 *  (or set of source vertices) in a digraph. For versions that find the paths,
 *  see {@link DepthFirstDirectedPaths} and {@link BreadthFirstDirectedPaths}.
 *  <p>
 *  This implementation uses depth-first search.
 *  The constructor takes time proportional to <em>V</em> + <em>E</em>
 *  (in the worst case),
 *  where <em>V</em> is the number of vertices and <em>E</em> is the number of edges.
 *  <p>
 *  For additional documentation,
 *  see <a href="http://algs4.cs.princeton.edu/42digraph">Section 4.2</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class DirectedDFS {
    private boolean[] marked;  // marked[v] = true if v is reachable
                               // from source (or sources)
    private int count;         // number of vertices reachable from s

    /**
     * Computes the vertices in digraph {@code G} that are
     * reachable from the source vertex {@code s}.
     * @param G the digraph
     * @param s the source vertex
     * @throws IllegalArgumentException unless {@code 0 <= s < V}
     */
    public DirectedDFS(Digraph G, int s) {
        marked = new boolean[G.V()];
        validateVertex(s);
        dfs(G, s);
    }

    /**
     * Computes the vertices in digraph {@code G} that are
     * connected to any of the source vertices {@code sources}.
     * @param G the graph
     * @param sources the source vertices
     * @throws IllegalArgumentException unless {@code 0 <= s < V}
     *         for each vertex {@code s} in {@code sources}
     */
    public DirectedDFS(Digraph G, Iterable<Integer> sources) {
        marked = new boolean[G.V()];
        validateVertices(sources);
        for (int v : sources) {
            if (!marked[v]) dfs(G, v);
        }
    }

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

    /**
     * Is there a directed path from the source vertex (or any
     * of the source vertices) and vertex {@code v}?
     * @param  v the vertex
     * @return {@code true} if there is a directed path, {@code false} otherwise
     * @throws IllegalArgumentException unless {@code 0 <= v < V}
     */
    public boolean marked(int v) {
        validateVertex(v);
        return marked[v];
    }

    /**
     * Returns the number of vertices reachable from the source vertex
     * (or source vertices).
     * @return the number of vertices reachable from the source vertex
     *   (or source vertices)
     */
    public int count() {
        return count;
    }

    // throw an IllegalArgumentException unless {@code 0 <= v < V}
    private void validateVertex(int v) {
        int V = marked.length;
        if (v < 0 || v >= V)
            throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1));
    }

    // throw an IllegalArgumentException unless {@code 0 <= v < V}
    private void validateVertices(Iterable<Integer> vertices) {
        if (vertices == null) {
            throw new IllegalArgumentException("argument is null");
        }
        int V = marked.length;
        for (int v : vertices) {
            if (v < 0 || v >= V) {
                throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1));
            }
        }
    }


    /**
     * Unit tests the {@code DirectedDFS} data type.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {

        // read in digraph from command-line argument
        In in = new In(args[0]);
        Digraph G = new Digraph(in);

        // read in sources from command-line arguments
        Bag<Integer> sources = new Bag<Integer>();
        for (int i = 1; i < args.length; i++) {
            int s = Integer.parseInt(args[i]);
            sources.add(s);
        }

        // multiple-source reachability
        DirectedDFS dfs = new DirectedDFS(G, sources);

        // print out vertices reachable from sources
        for (int v = 0; v < G.V(); v++) {
            if (dfs.marked(v)) StdOut.print(v + " ");
        }
        StdOut.println();
    }

}

/******************************************************************************
 *  Copyright 2002-2016, Robert Sedgewick and Kevin Wayne.
 *
 *  This file is part of algs4.jar, which accompanies the textbook
 *
 *      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
 *      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
 *      http://algs4.cs.princeton.edu
 *
 *
 *  algs4.jar is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  algs4.jar is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with algs4.jar.  If not, see http://www.gnu.org/licenses.
 ******************************************************************************/


Last updated: Fri Jun 23 14:11:27 EDT 2017.